N.01.1 I.C'H
114
4(' N.01.1 I.C'H
Transcript of N.01.1 I.C'H
4('N
.01.1 I.C'H
PRE
FAC
E.
AN
atte
mpt
has
bee
n m
ade
to s
ot f
orth
in th
ese
NoT
ics
the
subj
ect
ofel
emen
tary
tech
nica
lT
eleg
raph
y an
d T
elep
hony
to m
eet
conc
isel
y 'a
nd a
dequ
atel
y th
e re
quir
emen
ts o
f th
e Sy
llabu
s of
the
City
and
Gui
lds
of L
ondo
n In
stitu
te's
Exa
min
atio
n in
the
Ord
inar
y G
rad'
e..:
Cle
arne
ss o
f m
eani
ng, t
oget
her
with
an
accu
rate
elu
cida
tion
of e
ssen
tial
prin
cipl
es, f
orm
ulm
, law
s, e
tc.,
has
been
the
pred
omin
atin
g ai
m o
f th
e,au
thor
s th
roug
hout
;bu
t the
out
stan
ding
fea
ture
, whi
ch it
is h
oped
/pr
ove
of s
peci
al v
alue
to th
e av
erag
e st
uden
t, is
the
num
erou
s fu
llysi
mpl
y w
orke
d ar
ithm
etic
al p
robl
ems
and
exam
ples
.
Prim
arily
thes
e N
OT
ES
wer
e w
ritte
n fo
r th
e T
eleg
raph
Chr
onic
l4en
able
stu
dent
s in
the
outly
ing
dist
rict
s, w
here
fac
ilitie
s fo
rrg
s,as
ses
do n
ot e
xist
, to
obta
in th
e ne
cess
ary
know
ledg
e of
t-i
t, in
cide
ntal
ly, i
t is
thou
ght t
hat t
he w
ork
in it
s pr
esen
t fax
not b
e un
acce
ptab
le to
teac
hers
, who
will
pro
babl
y fi
nd th
e de
raan
t...
the
Inst
itute
's S
ylla
bus
ampl
y an
d sy
stem
atic
ally
met
.
The
aut
hors
hav
e be
en f
requ
ently
ask
ed f
or a
dvic
e w
ith r
egar
d to
the
best
met
hod
to a
dopt
to e
nsur
e su
cces
s at
var
ious
exa
min
atio
ns.
The
yha
ve f
ound
aft
er s
ever
al y
ears
' exp
erie
nce
of c
lass
-w
ork
that
a p
ersi
sten
tlyca
rrie
d ou
t sys
tem
of
hom
e -w
ork
is a
n in
valu
able
hel
p.T
he s
tude
ntsh
ould
be
set q
uest
ions
bas
ed u
pon
the
wor
k of
pre
viou
s le
ctur
es, a
nd,
afte
r re
adin
g ot
her
mat
ter
rela
ting
to th
e su
bjec
t of
the
ques
tions
, he
shou
ld e
xpre
ss in
his
ow
n w
ords
his
idea
s of
the
answ
ers
requ
ired
.H
esh
ould
quo
te a
law
and
fur
nish
a s
ketc
h w
hene
ver
prac
ticab
le.
The
teac
her
in tu
rn s
houl
d ve
ry c
aref
ully
exa
min
e su
ch a
nsw
ers,
cor
rect
ing
acid
enc
oura
ging
the
stud
ent b
y m
argi
nal n
otes
at
ever
y se
mbl
ance
,of
erro
r or
con
fusi
on o
f th
ough
t.W
hen
this
sys
tem
of
co-o
pera
tion
isad
opte
d an
d pe
rsev
ered
with
the
high
est r
esul
ts a
re in
vari
ably
ass
ured
.
In c
oncl
usio
n, th
e w
rite
rs d
esir
eto
exp
ress
thei
r in
debt
edne
ss to
the
auth
ors
of th
e m
any
stan
dard
wor
ks o
n th
e su
bjec
ts o
f te
chni
cal
Tel
egra
phy
and
Tel
epho
ny, a
nd a
lso
to th
e co
ntri
buto
rs to
the
vari
ous,
elec
tric
al p
erio
dica
ls d
ealin
g w
ith th
em f
rom
tim
e to
tim
e. 'Ow
I i
roe,
Sep
tem
ber,
190
4.
NO
TE
S O
N T
EL
EG
RA
PHY
.
CH
APT
ER
I.
EL
EC
TR
ICIT
Y A
ND
MA
GN
ET
ISM
.
An
elem
enta
ry k
now
ledg
e of
ele
ctri
city
and
mag
netis
m is
ess
entia
l to
,,-th
e st
uden
t of
tele
grap
hy a
nd te
leph
ony.
Seve
ral t
heor
ies
have
bee
n se
t:'
)up
as
to th
e na
,*ur
e of
ele
ctri
city
, but
as
they
are
of
an a
cade
mic
al r
athe
r'
''th
an a
pra
ctic
ai c
hara
cter
the
usua
lly a
ccep
ted
view
s w
ill b
e de
alt w
ith.
i k"e
lect
rici
ty in
a s
tate
of
rest
may
be
said
to p
erva
de a
ll na
ture
, but
its
i'1'1
",ee
ts a
re n
ot a
ppar
ent u
ntil
it is
dis
turb
ed. W
hen
two
bodi
es a
re r
ubbe
d
1
;eth
er a
nd th
en s
epar
ated
a r
edis
trib
utio
n of
the
elec
tric
ity q
uies
cent
'
each
may
be
said
to ta
ke p
lace
.T
hey
have
bee
n br
ough
t fro
m a
`.!C
.iele
rittr
ifie
d to
an
elec
trif
ied
cond
ition
.T
he a
ssum
ptio
n is
that
,_ a
le
'
Oss
esSe
s a
grea
ter
amou
nt o
f el
ectr
icity
and
the
othe
r a
smal
ler
amou
ntth
an b
efor
e.T
he tw
o co
nditi
ons
are
term
ed p
ositi
ve e
lect
rifi
catio
n an
dne
gativ
e el
ectr
ific
atio
n re
spec
tivel
y.W
hen
a dr
y gl
ass
rod
is r
ubbe
d w
ith a
pie
ce o
f si
lk, b
oth
the
glas
s an
dth
e si
lk b
ecom
e el
ectr
ifie
d, a
nd, u
pon
sepa
ratin
g th
em, e
xper
imen
t sho
ws
that
eac
h po
sses
ses
prop
ertie
s w
hich
it d
id n
ot p
revi
ousl
y po
sses
s.T
hegl
ass
rod
beco
mes
pos
itive
ly e
lect
rifi
ed a
nd ,t
he s
ilk r
ubbe
r ne
gativ
ely
elec
trif
ied.
Fric
tion,
then
, is
one
of th
e ca
uses
of
redi
stri
butio
n w
hich
prod
uces
ele
ctri
fica
tion.
Itis
onl
y by
the
effe
cts
of e
lect
rici
ty th
at it
spr
esen
ce m
ay b
e de
term
ined
.B
odie
s si
mila
rly
elec
trif
ied
repe
l eac
h ot
her,
and
bod
ies
diss
imila
rly
elec
trif
ied
attr
act e
ach
othe
r.W
hen
two
bodi
es a
re e
lect
rifi
ed b
y be
ing
rubb
ed to
geth
er th
e ch
arge
of
elec
tric
ity g
ener
ated
on
each
is th
e sa
me
in a
mou
nt b
ut d
iffe
rent
in k
ind,
the
one
bein
g po
sitiv
ely
elec
trif
ied
and
the
othe
r ne
gativ
ely
elec
trif
ied.
Ifth
e tw
o ch
arge
s so
pro
duce
d be
allo
wed
to r
ecom
bine
, equ
ilibr
ium
will
be
rest
ored
.T
here
is a
lway
s a
tend
ency
for
unl
ike
char
ges
to c
ombi
ne a
ndne
utra
lise
each
oth
er, a
nd m
utua
l attr
actio
n, in
the
effo
rt to
pro
duce
equi
libri
um, r
esul
ts. B
odie
s el
ectr
ifie
d w
ith li
ke c
harg
es, w
heth
er p
ositi
veor
neg
ativ
e, r
epel
eac
h ot
her.
An
elec
trif
ied
body
has
the
pow
er to
per
form
cer
tain
fun
ctio
ns w
hich
itdi
d no
t pos
sess
in a
n un
elec
trif
ied
stat
e.It
has
the
pow
er o
f re
pelli
nglig
ht b
odie
siiim
ilarl
y ch
arge
d, a
nd it
als
o ha
s th
e po
wer
of
attr
actin
g lig
htun
elec
trif
ied
bodi
es a
nd b
odie
s op
posi
tely
cha
rged
.A
n el
ectr
ifie
d gl
ass
4N
OT
ES
ON
TE
LE
GR
APH
Y.
rod
on b
eing
bro
ught
nea
r sc
raps
of
pape
r, f
eath
ers,
or
othe
r lig
htsu
bsta
nces
attr
acts
them
.,T
he r
od h
as a
ssum
ed a
pow
er, o
r po
tent
ialit
y.T
he te
rm e
lect
ric
pote
ntia
l is,
gen
eral
ly s
peak
ing,
the
firs
t stu
mbl
ing
bloc
k to
the
elem
enta
ry s
tude
nt, b
ut it
will
be
suff
icie
nt to
des
crib
e it
asth
e po
wer
to d
o w
ork
poss
esse
d by
all
elec
trif
ied
bodi
es. T
he p
oten
tial
of a
n el
ectr
ifie
d bo
dy d
epen
ds u
pon
the
amou
nt o
f el
ectr
icity
it c
onta
ins
and
the
capa
city
the
body
has
for
hold
ing
it.A
llun
elec
trif
ied
bodi
es a
re s
aid
to b
e at
zer
o po
tent
ial,
and
elec
trif
ied
bodi
es a
re s
aid
to b
eat
eith
er p
ositi
ve o
r ne
gativ
e po
tent
ial.
Ele
ctri
cal p
oten
tial m
ay b
e co
n-si
dere
d as
ele
ctri
cal ,
pres
sure
or
leve
l, fo
r, a
s w
ater
impe
lled
by th
e fo
rce
ofgr
avity
run
s do
wn
a hi
ll, s
o a
tran
sfer
ence
of
elec
tric
al e
nerg
y w
ill ta
kepl
ace
from
a p
oint
of
high
ele
ctri
cal l
evel
to a
poi
nt o
f lo
w e
lect
rica
lD
iffe
renc
e of
pot
entia
l is
term
ed e
lect
rom
otiv
e fo
rce,
and
is th
e pr
ieat
whi
ch f
orce
s el
ectr
icity
thro
ugh
the
cond
ucto
r, in
the
form
of
a cu
rren
t tef
fect
ele
ctri
cal e
quili
briu
m.
CO
ND
UC
TO
RS
AN
D I
NSU
LA
TO
RS.
All
subs
tanc
es d
o no
t pos
sess
the
prop
erty
of
allo
win
g el
ectr
icity
toth
roug
h th
em to
the
sam
e de
gree
.B
odie
s w
hich
allo
w e
lect
rici
ty to
pal
thro
ugh
them
fre
ely
are
term
ed c
ondu
ctor
s ; w
here
as, b
odie
s w
hich
ret
ard
the
pass
age
of e
lect
rici
ty in
a m
arke
d de
gree
are
cal
led
insu
lato
rs o
r no
r,,
cond
ucto
rs.
The
term
s, h
owev
er, a
re o
nly
rela
tive,
for
all
bodi
es, e
ven'
cond
ucto
rs, r
esis
tth
e fl
ow o
f el
ectr
icity
to a
cert
ain
exte
nt.
Thi
spr
oper
ty is
cal
led
resi
stan
ce, a
nd m
ay b
e de
fine
d as
the
prop
erty
pos
sess
edby
all
bodi
es in
var
ying
deg
ree,
by
virt
ue o
f w
hich
the
tran
sfer
ence
of
elec
tric
ity to
pro
duce
equ
ilibr
ium
is r
etar
ded.
All
met
als
are
cond
ucto
rs, i
.e.,
they
off
er s
mal
l res
ista
nce
to th
epa
ssag
eof
ele
ctri
city
.C
arbo
n, w
ater
, and
aci
d so
lutio
ns a
re s
emi -
cond
ucto
rs, a
sth
eypr
esen
t a c
ompa
rativ
ely
high
res
ista
nce
to th
etr
ansf
eren
ce o
fel
ectr
ical
ene
rgy.
Indi
a -r
ubbe
r, g
utta
-per
cha,
ebo
nite
, oil,
por
cela
in, w
ax,
and
dry
air
are
insu
lato
rs, a
s th
e re
sist
ance
of
eith
er o
f th
ese
bodi
es is
prac
tical
ly in
fini
te.
MA
GN
ET
ISM
.
The
re a
re tw
o ki
nds
of m
agne
ts, n
atur
al a
nd a
rtif
icia
l. A
nat
ural
mag
net
is n
aile
d a
lode
ston
e, a
nd is
a c
ompo
und
of ir
on a
nd o
xyge
n fo
und
larg
ely
natu
re. I
ts c
hem
ical
for
mul
a is
Fe:
, 0, a
nd a
ttent
ion
was
fir
st d
irec
ted
to I
L b
y its
pow
er o
f at
trac
ting
iron
.T
he m
agno
lia p
rope
rtie
s of
the
lode
ston
e m
ay b
e 1,
1.11
,110
0mA
to ir
on a
ndst
eel l
ci e
el/o
ral w
ays.
Tak
e a
piec
e of
ord
inar
y w
ittch
spri
ng a
nd r
ub it
fro
men
d to
end
a n
umbe
r of
tim
es, i
n on
e dl
i:oet
ion
'oily
, with
the
lode
ston
e,T
he s
teel
will
1,,,
w a
ttrac
t oth
er p
iece
s of
sto
ol m
od I
ron,
hav
ing
beco
me
wha
t la
Lor
mod
uu
aim
mIi
oial
inog
not.
It a
inag
ool,
be e
uspe
nded
or
pivo
ted
Nu
WI
lei b
e on
pabl
o of
lota
tion
In a
hurl
ruub
ul y
ludi
u, it
will
()m
u to
met
With
16o
6wo
cede
poi
nbld
t ono
Int
l()
NO
TE
S O
N T
EL
EG
RA
PHY
.5
dire
ctio
n of
the
nort
h ge
ogra
phic
al p
ole,
and
the
othe
r in
the
dire
ctio
nof
the
sout
h ge
ogra
phic
al p
olo;
mor
eove
r, th
e sa
me
end
of th
e m
agne
t will
alw
ays
poin
t in
the
sam
e di
rect
ion.
The
se f
acts
lead
to th
e co
nclu
sion
that
ther
e is
som
e in
flue
nce,
or
forc
e, a
ctin
g up
on th
e m
agne
t.T
his
dire
ctiv
efo
rce
is d
ue'4
o th
e ea
rth,
whi
ch e
xhib
its m
agne
tic p
rope
rtie
s.T
heen
d of
the
mag
net w
hich
poi
nts
tow
ards
the
nort
h is
cal
led
its n
orth
-
seek
ing
pole
, whi
le th
e ot
her
end
is c
alle
d its
sou
th -
seek
ing
pole
.T
he a
ttrac
tive
pow
er o
f a
mag
net i
s no
t eve
nly
dist
ribu
ted
alon
g its
Who
le le
ngth
.Pl
unge
a m
agne
t int
o ir
on f
iling
s an
d no
te w
hat h
appe
ns.
the
pole
s th
e fi
lings
adh
ere
to th
e m
agne
t in
larg
e cl
uste
rs, b
ut th
ey°C
reas
e in
num
ber
alon
g th
e m
agne
t tow
ards
the
cent
re, a
t Whi
ch p
oint
o f;
lings
are
attr
acte
d.ea
rth
is a
mag
net h
avin
g its
mag
netic
pol
es s
ituat
ed n
ear
the
nort
he
%14
xiau
th ,g
eogr
aphi
cal p
oles
.T
he m
agne
tic a
nd th
e ge
ogra
phic
al p
oles
,"e
ver,
do
not e
xact
ly c
oinc
ide,
and
the
mag
netic
mer
idia
n of
any
plac
eay
be
cons
ider
ed a
s an
imag
inar
y pl
ane
pass
ing
thro
ugh
the
mag
netic
of th
e ea
rth
and
the
poin
t im
med
iate
ly o
verh
ead.
A m
agne
tde
d in
suc
h a
man
ner
as to
be
capa
ble
of r
otat
ing
in a
hor
izon
tal
ne' w
ill c
ome
to r
est i
n th
e m
agne
tic m
erid
ian,
i.e.
, poi
ntin
g to
.A
lik.-
Afo
rth
and
,sou
th m
agne
tic p
oles
.`
eA
ir "
-The
fir
st la
w o
f m
agne
tism
sta
tes
that
unl
ike
mag
netic
pol
es a
ttest
each
oth
er, a
nd li
ke m
agne
tic p
oles
rep
el e
ach
othe
r.Fr
om a
con
side
eatio
n of
this
the
read
er w
ill r
eadi
ly s
ee th
e re
ason
why
the
mag
net c
omes
to r
est i
n th
e m
agne
tic m
erid
ian.
The
two
pole
s of
the
mag
net a
re in
flue
nced
by
the
mag
netic
pol
es o
f th
e ea
rth.
The
nor
th -
seek
ing
pole
of
the
mag
net i
s at
trac
ted
by th
e no
rth
mag
netic
pol
e of
the
eart
h an
d re
pelle
d by
the
eart
h's
sout
h m
agne
tic p
ole.
The
sou
th -
seek
ing
pole
of
the
mag
net i
s in
flue
nced
in a
sim
ilar
man
ner,
bei
ngat
trac
ted
and
repe
lled
by th
e so
uth
and
nort
h m
agne
tic p
oles
of
the
eart
hre
spec
tivel
y.It
sho
uld,
how
ever
, be
clea
rly
unde
rsto
od th
at th
e m
agne
tis
not
attr
acte
d bo
dily
tow
ards
eith
er p
ole
of th
e ea
rth.
The
term
s"
attr
act "
and
." r
epel
" a
re u
sed
to in
dica
te th
e di
rect
ion
in w
hich
the
susp
ende
d m
agne
t will
turn
.T
he e
arth
's in
flue
nce
is d
irec
tive
and
not
attr
activ
e, f
or th
e ea
rth'
s no
rth
mag
netic
pol
e w
ill a
ttrac
t the
one
pol
eof
the
mag
net w
ith th
e sa
me
forc
e as
it w
ill r
epel
the
othe
r.
MA
GN
ET
IC S
UB
STA
NC
ES.
All
bodi
es a
re n
ot c
apab
le o
f be
ing
mag
netis
ed.
Tho
se w
hich
can
be
mag
netis
ed a
re f
ew in
num
ber,
and
are
cal
led
mag
netic
sub
stan
ces.
The
read
er w
ill r
eadi
ly c
all t
o m
ind
iron
and
ste
el a
s be
ing
mag
netic
sub
stan
ces.
The
re a
re, h
owev
er, a
few
oth
er s
uch
bodi
es, v
iz.,
nick
el, m
anga
nese
,co
balt,
and
chr
omiu
m.
The
phy
sica
l the
ory
of m
agne
tism
is th
e on
e ge
nera
lly a
ccep
ted,
and
supp
oses
that
the
mol
ecul
es w
hich
mak
e up
the
mas
s of
a m
agne
tic
6ttc
dtS
014
tttte
ittA
PHY
.
subs
tanc
e ar
e th
emse
lves
mag
nets
.T
he a
ct o
fm
agne
tisat
ion
is th
ear
rang
emen
t of
the
mol
ecul
es in
a d
efin
ite o
rder
,th
e si
mila
r po
les
of th
em
olec
ules
all
poin
ting
in o
ne d
irec
tion.
(Fig
. 1.)
Thi
s is
bor
ne o
ut b
y
expe
rim
ent.
Whe
n a
mag
net i
s br
oken
into
two
or m
ore
part
s, e
ach
part
is it
self
a c
ompl
ete
mag
net.
The
mag
net m
ay b
e br
oken
!ipd
efin
itely
until
the
smal
lest
par
ticle
s po
ssib
le a
re a
rriv
edat
, and
eac
h pa
rtic
lew
ill e
xhib
it th
e sa
me
prop
ertie
s as
the
who
le m
agne
t, th
ough
nec
essa
rily
in a
loss
mar
ked
degr
ee.
A s
mal
l tes
t tub
e fi
lled
with
iron
fili
ngs
in th
eir
norm
al c
ondi
tion
does
not
evi
nce
mag
netic
pro
pert
ies;
but
pas
s on
e po
le
Is 'I
scp
e1,
71 t4
\ (,1
1/11
r,
Bef
ore
141
NA
di d
i z1.
1ta
,is
N3
diC
IA d
a
lifte
r
FIG
.f.
of a
mag
net a
long
tho
test
tube
a n
umbe
r of
tim
es in
one
dir
ectio
n,an
d
it w
ill b
e se
en th
at th
e fi
lings
are
now
arr
ange
d in
ord
er.
The
y ha
ve lo
stth
eir
Lig
gled
y-pi
ggle
dy c
ondi
tion,
and
hav
e be
en a
rran
ged
leng
thw
ise
alon
g th
e tu
be.
The
tube
of
filin
gs is
now
a m
agne
t, an
d ex
hibi
ts th
esa
me
prop
ertie
s as
an
ordi
nary
mag
netis
edba
r.U
pon
shak
ing
the
tube
the
filin
gs b
ecom
e di
sord
ered
, and
the
mas
s, a
s a
who
le, l
oses
its
mag
netic
pow
ers.
All
mag
netic
sub
stan
ces
cann
ot b
e m
agne
tised
with
the
sam
e fa
cilit
y.So
ft ir
on is
rea
dily
mag
netis
ed, w
here
as, h
ard
-tem
pere
d st
eel i
s m
agne
tised
with
com
para
tive
diff
ictil
ty.
The
iron
, how
ever
, rem
ains
a m
agne
t onl
y as
long
as
the
effo
rt to
mag
netis
e it
is s
usta
ined
.O
n th
e ot
her
hand
, ste
elis
not
rea
dily
mag
netis
ed, b
ut w
hen
once
this
con
ditio
n is
arr
ived
at
the
stee
l per
man
ently
ret
ains
its
mag
netic
pro
pert
ies.
The
dif
fere
nce
betw
een
stee
l and
iron
in th
is r
espe
ct is
pro
babl
y du
e to
the
mol
ecul
arco
nstr
uctio
n of
the
two
subs
tanc
es.
The
par
ticle
s of
the
iron
are
mor
e
easi
ly a
rran
ged
by th
e pr
oces
s of
mag
netis
atio
nth
an th
ose
of th
e st
eel,
but w
hen
the
latte
r ha
s be
en m
agne
tised
the
part
icle
s re
mai
n fi
xed.
In
the
case
of
iron
the
part
icle
s re
turn
to th
eir
norm
al d
isor
dere
d co
nditi
on.
Tbi
s pr
oper
ty p
osse
ssed
by
stee
lis
som
etim
es c
alle
d re
tent
ivity
, or
coer
cive
for
ce.
NO
TE
S O
N T
EL
EG
RA
PHY
.
LIN
ES
OF
FOR
CE
.
A m
agne
t is
surr
ound
ed b
y a
fiel
d of
for
ce w
hich
ext
ends
so f
ar a
s th
ein
flue
nce
of th
e m
agne
t is
felt.
Lin
es o
f fo
rce
perv
ade
this
mag
netic
fie
ldin
var
ying
deg
rees
of
inte
nsity
, and
den
ote
its e
xten
t.T
hey
are
som
e-tim
es c
alle
d lin
es o
f m
agne
tic in
duct
ion,
and
are
in th
esh
ape
of c
lose
dcu
rves
abo
ut th
e m
agne
t.T
he in
tens
ity o
f th
ese
lines
is g
reat
est
near
the
ends
, or
pole
s,of
the
mag
net.
Tak
e an
ord
inar
y ba
r m
agne
t and
pla
ceit
imm
edia
tely
ben
eath
ash
eet
ofca
rdbo
ard.
Upo
n th
e ca
rdbo
ard
spri
nkle
iron
fili
ngs,
and
not
e ho
w th
ey a
rran
ge th
emse
lves
.N
ear
the
pole
s th
e fi
lings
are
see
n to
be
in c
lust
ers,
but
tow
ards
the
cent
re o
fth
e m
agne
t the
y ar
e fe
w in
num
ber.
A c
lose
r ex
amin
atio
n sh
ows
that
the
filin
gs h
ave
arra
nged
them
selv
es le
ngth
wis
e in
the
form
of
curv
es, a
ssh
own
in F
ig. 2
.
FR. 2
.
MA
GN
ET
IC I
ND
UC
TIO
N.
Whe
n a
piec
e of
iron
is b
roug
ht in
to a
mag
netic
fie
ld it
bec
omes
am
agne
t und
er th
e in
duct
ive
infl
uenc
e of
the
mag
net.
Plac
e a
piec
e of
unm
agne
tised
iron
in c
onta
ct w
ith o
ne p
ole
of a
mag
net,
and
it w
ill b
ese
en,
by e
xper
imen
t, th
at th
e ir
on h
as a
ssum
ed m
agne
tic p
rope
rtie
s.T
he e
ndof
the
iron
in c
onta
ct w
ith th
e m
agne
t will
be
ofop
posi
te p
olar
ity to
the
pole
of
the
mag
net w
ith w
hich
it is
in c
onta
ct.
(Fig
. 3.)
IN11
2hgn
et51
1iro
t)31
FIG
, 3If
the
iron
be
plac
ed a
t a li
ttle
dist
ance
fro
m th
em
agne
t the
sam
eef
fect
s w
ill b
e ap
pare
nt, t
he n
ear
end
assu
min
g an
opp
osite
pola
rity
to th
ead
jace
nt p
ole
of th
e m
agne
t.T
he o
ther
end
of
the
iron
will
, of
nece
ssity
,
Rot
eson
Cei
egra
piv
e,
D'
A S
IMP
LE E
XP
OS
ITIO
N O
F T
HE
RU
DIM
EN
TS
OF
TE
CH
NIC
AL
TE
LEG
RA
PH
Y A
ND
TE
LEP
HO
NY
.
BY
A. O
. PR
AT
T a
nd G
. M00
0,M
erch
ant V
entu
rers
' Tec
hnic
al C
olle
ge, B
risto
l,an
d P
osta
l Tel
egra
phs,
Bris
tol.
215
PAG
ES,
With
126
Illu
stra
tions
and
52
fully
wor
ked
Mat
hem
atic
al E
xam
ples
.
LO
ND
ON
:
PO -
OPE
RA
TIV
E P
RIN
TIN
G S
OC
IET
Y. L
IMIT
ED
, TU
DO
R S
T.,
NE
W B
RID
GE
ST
., E
.C. ;
AN
D A
T M
AN
CH
EST
ER
AN
D N
EW
CA
STL
E.
1901
.
82N
OT
ES
ON
TE
LE
GR
APH
Y.
inco
mpl
ete.
By
depr
essi
ng th
e ri
ght-
hand
tapp
er th
e po
sitiv
e po
le o
f th
eba
ttery
is c
onne
cted
to th
e lin
e by
way
of
the
low
er s
trip
, and
the
othe
rpo
le r
emai
ns e
arth
-co
nnec
ted.
By
rele
asin
g th
e ri
ght-
hand
and
dep
ress
ing
the
loft
hand
tapp
er a
rev
ersa
l of
the
batte
ry c
onne
ctio
n is
eff
ecte
d.Fo
rpr
actic
al p
urpo
ses
the
leve
rs a
re m
ade
of e
boni
te w
ith s
uita
ble
cont
act
poin
ts a
rran
ged
to m
ake
the
requ
ired
con
nect
ions
.(F
ig. 4
2.)
The
mos
t eff
icie
nt f
orm
of
rece
ivin
g ap
para
tus
is th
at d
evis
ed b
ySp
agno
letti
.A
coi
l of
wir
e in
two
sect
ions
is w
ound
upon
two
bobb
ins
moo
....
...t.,
.,4,
J.:
FIG
.41.
insi
de o
f w
hich
a p
ecul
iarl
y -s
hape
d ne
edle
, ren
dere
d m
agne
tic b
y tw
opo
wer
ful p
erm
anen
t mag
nets
of
the
hors
esho
e ty
pe, i
s de
flec
ted
by th
eac
tion
of th
e cu
rren
t.(F
ig.
41.)
The
upp
er a
nd lo
wer
sec
tions
of
the
need
le a
re m
agne
tical
ly s
epar
ated
by
a sm
all s
trip
of
spel
ter.
The
low
eren
d of
the
uppe
r se
ctio
n of
the
need
le a
nd th
e up
per
end
of th
e lo
wer
sect
ion
aro
exte
nded
and
for
m th
e ax
le u
pon
whi
ch th
e ne
edle
turn
s.T
he m
agne
ts a
re a
rran
ged
so th
at th
eir
sim
ilar
pole
s ac
t ind
uctiv
ely
upon
the
sam
e en
d of
the
axle
and
pro
duce
opp
osite
pol
ariti
es a
t the
free
end
s of
the
need
le.
The
Nor
th .s
eeki
ng p
ole
is in
vari
ably
at t
hebo
ttom
, so
that
the
indu
ctiv
ein
flue
nce
ofth
eea
rth
may
ass
ist i
nre
tain
ing
the
mag
netic
str
engt
h of
the
com
bina
tion.
The
mag
netic
effe
ct o
f th
e cu
rren
t upo
n th
e ne
edle
is in
crea
sed
by th
e ex
trem
ities
of
the
latte
r be
ing
wid
ened
, and
als
o by
clo
sely
win
ding
the
coil
upon
the
bobb
ins,
whi
ch a
re f
orm
ed to
allo
w ju
st s
uffi
cien
t spa
ce f
or th
e fr
ee m
ove-
men
t of
the
need
le w
ithin
them
.T
he n
eedl
e is
piv
otte
d ex
actly
mid
-w
ay
NO
TE
S O
N T
EL
EG
RA
PHY
.83
betw
een
the
two
sect
ions
of
the
coils
.A
ttach
ed to
the
need
le is
a li
ght
poin
ter
whi
ch o
beys
the
mov
emen
ts o
f th
e ne
edle
and
indi
cate
s at
the
exte
rior
of
the
case
the
sign
als
whi
char
ebe
ing
rece
ived
with
in.
Tw
o sm
all i
vory
stu
ds li
mit
the
defl
ectio
ns o
f th
e po
inte
r....
The
latte
rbe
ats
with
gre
at f
irm
ness
upo
n th
em, a
nd b
y th
is m
eans
the
visi
ble
sign
als
are
mor
e ea
sily
rea
d.
The
rec
eivi
ng in
stru
men
t is
in b
oth
the
send
ing
and
the
rece
ivin
gci
rcui
ts, a
nd a
cts
as a
n ef
fici
ent s
ubst
itute
for
a c
ircu
it ga
lvan
omet
er.
The
def
lect
ions
are
alw
ays
in th
e sa
me
dire
ctio
n as
that
of
the
curr
ents
prod
ucin
g th
em, i
.e.,
a cu
rren
t pas
sing
thro
ugh
the
coil
from
left
to r
ight
will
cau
se th
e up
per
port
ion
ofth
e ne
edle
to d
efle
ct to
war
ds th
e ri
ght
hand
.T
his
prin
cipl
e of
con
nect
ion
is a
dopt
ed in
join
ing
up a
ll ga
lvan
o-m
eter
s us
ed b
y th
e B
ritis
h Po
st O
ffic
e.
1
80N
OT
ES
ON
TE
LE
GR
APH
Y.
at B
is jo
ined
up.
The
line
is th
us p
ut to
ear
th v
ia th
e on
e -a
mpe
re f
use,
A c
arbo
n lig
htni
ng p
rote
ctor
is a
lso
incl
uded
in th
eve
ry n
eat a
rran
gem
ent,
and
is s
how
n at
P. T
he n
orm
al p
ath
for
an in
com
ing
curr
ent i
sth
roug
h th
eon
e an
ipin
.e f
use,
hea
t coi
l, so
lder
join
t and
spr
ing
to th
e in
stru
men
ts.
The
one
-am
pCre
fus
e is
a p
rote
ctio
n fr
om c
urre
nts
grea
tly in
exce
ss o
fth
ose
used
for
tele
grap
h pu
rpos
es.
It is
em
ploy
ed w
here
a p
ossi
bilit
y of
a co
ntac
t with
the
cond
ucto
rs o
f el
ectr
ic tr
actio
n or
ele
ctri
c lig
htin
gst
yste
ms
exis
t.PR
OT
EC
TO
RS
FOR
CA
BL
ES.
The
eff
ects
of
light
ning
upo
n su
bmar
ine
cabl
es a
reve
ry s
erio
us, a
nd,
inor
der
to p
reve
nt d
amag
e, p
rote
ctor
s ha
ving
larg
e br
ass
plat
esar
eem
ploy
ed.
Mic
a is
use
d as
the
insu
latin
g m
ediu
m.
In th
e ca
ble
circ
uit
a fi
ne p
latin
um f
use
wir
e is
als
o us
ed in
con
junc
tion
with
a "
ree
l " ty
peof
pro
tect
or a
s an
ext
ra p
reca
utio
n.T
he la
tter
form
of
prot
ecto
r co
nsis
tsof
two
silk
-co
vere
d w
ires
twis
ted
toge
ther
and
wou
ndup
on a
box
-w
ood
bobb
in.
One
of
thes
e w
ires
is e
arth
-co
nnec
ted,
and
the
ethe
r is
pla
ced
in th
e lin
e ci
rcui
t.T
he p
assa
ge o
f a
light
ning
dis
char
ge th
roug
h th
ela
tter
brea
ks th
roug
h th
e in
sula
tion
of th
e w
ires
and
pres
erve
s th
e ca
ble
from
dam
age.
NO
TE
S O
N T
EL
EG
RA
PHY
.81
CH
APT
ER
X.
TH
E S
ING
LE
NE
ED
LE
.
The
dir
ectio
n in
whi
ch a
mag
netic
nee
dle
will
turn
whe
n un
der
the
infl
uenc
e of
a c
urre
nt d
epen
ds u
pon
the
dire
ctio
n in
whi
ch th
e cu
rren
tis
flow
ing.
The
rev
ersa
l of
the
curr
ent p
rodu
ces
a re
vers
al o
f th
e di
rect
ion
of th
e fo
rce
actin
g up
on th
e ne
edle
, con
sequ
ently
the
defl
ectio
ns m
aybe
cont
rolle
d by
a r
ever
sal o
f th
e cu
rren
t. In
the
sing
le n
eedl
e sy
stem
visi
ble
sign
als,
rep
rese
ntin
g th
e M
orse
cod
e, a
re p
rodu
ced
byco
mbi
natio
ns o
fde
flec
tions
of
a ve
rtic
al n
eedl
e to
the
left
and
rig
ht.
The
sin
gle
need
le s
yste
m c
onsi
sts
esse
ntia
lly o
f tw
o pa
rts,
one
of
whi
ch
repr
esen
ts th
e se
ndin
g an
d th
e ot
her
the
rece
ivin
g ap
para
tus.
The
sen
ding
sec
tion
is a
com
mut
ator
, or
curr
ent r
ever
ser,
and
usu
ally
com
pris
es tw
o ta
pper
s, le
vers
, or
peda
ls f
or c
onne
ctin
gth
e ba
ttery
to th
elin
e.B
y th
e de
pres
sion
of
one
leve
r th
e ne
gativ
e po
leof
the
batte
ry is
conn
ecte
d to
the
line,
whi
le a
dep
ress
ion
of th
e ot
her
join
s up
the
posi
tive
pole
, and
the
dire
ctio
n of
the
curr
ent i
s co
nseq
uent
lyre
vers
ed a
t will
.W
hen
one
leve
r is
dep
ress
ed th
e ot
her
leve
r is
nor
mal
, and
the
batte
ryci
rcui
t is
com
plet
ed th
roug
h th
e la
tter.
Fig.
40
show
s th
e th
eory
of
the
com
mut
ator
sim
ply.
The
leve
rs a
re c
onne
cted
the
one
to e
arth
and
the
othe
r to
line
.T
wo
met
al c
ross
-co
nnec
ting
stri
ps,
to w
hich
the
pole
sof
the
batte
ry a
re jo
ined
,ar
e sh
own
atri
ght a
ngle
s to
the
met
allo
vers
, one
bei
ng a
bove
and
the
othe
r be
low
them
.W
hen
both
tapp
ers
are
at r
est t
hey
are
conn
ecte
d w
ith th
e up
per
stri
p an
d on
e po
leof
the
batte
ry, t
he o
ther
pol
e be
ing
left
dis
conn
ecte
d, a
ndth
e ba
ttery
cir
cuit
is
86N
OT
ES
ON
TE
LE
GR
APH
Y.
is c
onse
quen
tly v
ery
suita
ble
for
the
wor
k re
quir
ed o
f it.
Tw
o el
ectr
o-m
agne
ts, t
o bo
th c
ores
of
whi
ch tw
o so
ft ir
on p
ole
-pie
ces,
one
at e
ach
end,
are
atta
ched
, are
in th
e lin
e ci
rcui
t.B
etw
een
the
two
uppe
r an
d al
sobe
twee
n th
e tw
o lo
wer
pol
e -p
iece
s a
soft
iron
tong
ue, r
ende
red
mag
netic
by th
e in
duct
ive
actio
n of
a s
tron
g pe
rman
ent m
agne
t, is
fitt
ed. T
he to
ngue
sar
e co
nnec
ted
by m
eans
of
a lig
ht d
elic
atel
y -p
ivot
ed b
rass
rod
, to
whi
chth
ey a
ro f
ixed
at r
ight
ang
les.
The
per
man
ent m
agne
t is
so a
rran
ged
that
itsN
orth
-se
ekin
g po
leis
in c
lose
pro
xim
ityto
the
low
er to
ngue
or
arm
atur
e, w
hile
its
Sout
h -s
eeki
ng p
ole
is a
djac
ent
to th
e ar
mat
ure
fitte
d to
the
othe
r en
d of
the
conn
ectin
g ro
d.T
hepo
sitio
ns o
f th
ear
mat
ures
and
the
perm
anen
t mag
net a
re s
uch
that
the
extr
emity
ofth
eon
ew
hich
play
sbe
twee
nth
eup
per
pole
-pi
eces
is
nc 4
3
ofSo
uth
-see
king
pola
rity
,w
hile
that
ofth
elo
wer
one
poss
esse
san
opp
osite
pol
arity
(Fi
g. 4
3.)
On
acco
unt o
f th
e in
duce
d m
agne
tic c
on-
ditio
n of
the
tong
ues
the
rela
y is
sai
d to
be
pola
rise
d in
con
trad
istin
ctio
nto
the
type
of
inst
rum
ent i
n w
hich
the
tong
ues
are
not o
f de
fini
tepo
lari
ty.
The
coi
ls o
f th
e el
ectr
o-m
agne
ts a
re d
iffe
rent
ially
wou
nd, e
ach
sect
ion
havi
ng a
res
ista
nce
of 2
00 o
hms.
Four
term
inal
s ar
o at
tach
ed to
the
base
of th
e in
stru
men
t, an
d to
thes
e th
e en
ds o
f th
e co
ils a
re c
onne
cted
,B
ym
eans
of
bras
s st
raps
eith
er th
e "
seri
es "
or
the
" qu
antit
y "
met
hod
ofjo
inin
g up
the
coils
may
be
reso
rted
to,
Fig.
44,
in w
hich
the
coils
are
join
ed in
ser
ies,
sho
ws
the
arra
ngem
ent r
ough
ly. T
he P
ost O
ffic
e st
anda
rdre
lay
owes
its
grea
t deg
ree
of s
ensi
bilit
y to
the
extr
eme
delic
acy
with
whi
ch it
is c
onst
ruct
ed, a
nd a
lso
to th
e fa
ct th
at f
our
forc
es a
ctup
on th
em
ovab
le a
rmat
ures
whe
n a
curr
ent p
asse
s th
roug
h th
e co
ils.
Supp
ose
that
the
coils
are
join
edin
seri
es,
and
that
acu
rren
tpa
sses
thro
ugh
them
fro
m "
U -
circ
le "
to D
.T
he u
pper
pol
e -p
iece
ofth
eri
ght-
hand
core
(Se
efi
g.43
)as
sum
es a
Nor
th -
seek
ing
pola
rity
and
the
low
er o
ne a
Sou
th -
seek
ing
pola
rity
.In
the
pole
-pi
eces
atta
ched
to th
e le
ft-h
and
core
exa
ctly
the
oppo
site
eff
ects
are
prod
uced
by
the
oppo
site
win
ding
of
the
coil,
the
uppe
r on
e be
com
ing
Sout
h -s
eeki
ng a
nd
NO
TE
S O
N T
EL
EG
RA
PHY
.87
the
low
er o
ne N
orth
-se
ekin
g.T
hese
eff
ects
may
be
read
ily p
rove
d by
the
appl
icat
ion
of A
mpe
re's
rul
e. A
littl
e co
nsid
erat
ion
will
mak
e it
clea
r th
atth
e m
utua
l for
ces
of a
ttrac
tion
and
repu
lsio
n ex
erte
d be
twee
n th
e po
le -
piec
es a
nd th
e ar
mat
ures
tend
to tu
rn th
e la
stna
med
in th
e sa
me
dire
ctio
n ;
the
arm
atur
es a
re a
ttrac
ted
by th
e ri
ght-
hand
pol
e -p
iece
s, a
ndre
pelle
d by
thos
e up
on th
e le
ft-h
and
side
.A
rev
ersa
l of
the
dire
ctio
n of
the
curr
ent w
ill, o
f co
urse
, pro
duce
an
oppo
site
turn
ing
effe
ct.
FIG
14.
Atta
ched
to th
e br
ass
spin
dle
whi
ch c
arri
es th
e ar
mat
ures
, and
imm
e-di
atel
y ab
ove
the
latte
r, is
a li
ght c
onta
ct to
ngue
whi
ch p
lays
bet
wee
n tw
oad
just
able
con
tact
scr
ews.
Thi
s to
ngue
mov
es w
ith th
e de
licat
ely
-piv
oted
spin
dle,
and
mak
es c
onta
ct w
ithei
ther
the
righ
t-ha
nd o
rth
ele
f t -
hand
con
tact
scr
ew in
acc
orda
nce
with
the
mov
emen
ts o
f th
e ar
mat
ures
.
FiG
.45.
The
con
tact
scr
ews
are
conn
ecte
d to
term
inal
s at
the
base
mar
ked
M a
ndS,
as
show
n in
Fig
s. 4
3 an
d 44
, whi
le th
e to
ngue
is in
con
nect
ion
with
the
term
inal
mar
ked
T, t
o w
hich
the
nega
tive
pole
of
the
loca
l bat
tery
isin
vari
ably
join
ed.
Whe
n no
cur
rent
is p
assi
ng th
roug
h th
e co
ils th
e m
ag-
netis
ed to
ngue
s or
arm
atur
es a
re a
ttrac
ted
to e
ither
one
sid
e or
the
othe
r by
the
soft
iron
pol
e -p
iece
s.T
he r
elat
ive
posi
tions
of
thes
e to
ngue
s to
the
pole
-pi
eces
is c
ontr
olle
d by
an
adju
stin
g sc
rew
pla
ced
near
the
foot
of th
e
84N
OT
ES
ON
TE
LE
GR
APH
Y.
The
res
ista
nce
of th
e in
stru
men
t is
200
ohm
s, a
nda
curr
ent s
tren
gth
of15
to 2
0 m
illia
mpe
res
is r
equi
red
to p
rodu
cea
wor
kabl
e ef
fect
.
Whe
n th
e un
iver
sal b
atte
ry s
yste
m is
empl
oyed
slig
ht m
odif
icat
ions
are
requ
ired
in jo
inin
g up
the
com
mut
ator
s to
pre
vent
sho
rt-c
ircu
iting
of
the
batte
ry s
houl
d bo
th p
edal
s be
sim
ulta
neou
sly
depr
esse
d.
Fig.
42
show
s th
e fu
ll co
nnec
tions
of
the
inst
rum
ent.
The
sha
ded
port
ion
of th
e co
mm
utat
or r
epre
sent
s th
e eb
onite
tapp
ers
thro
ugh
whi
chno
cur
rent
pas
ses.
The
pro
ject
ions
atta
ched
to th
e ta
pper
sar
e br
ass,
and
the
path
of
the
outg
oing
cur
rent
can
be
read
ily f
ollo
wed
fro
m th
e co
m-
mut
ator
to th
e up
and
dow
n lin
es b
yw
ay o
f th
e co
ntac
t poi
nts.
The
rece
ived
cur
rent
s pa
ss th
roug
h th
e br
ass
leve
rs a
nd b
ack
stop
s of
bot
hpe
dals
, and
then
ce to
line
or
eart
h.O
win
g to
its
sim
plic
ity o
f co
n-st
ruct
ion
the
sing
le n
eedl
e in
stru
men
t rar
ely
gets
out
of
orde
r, a
nd n
eeds
prac
tical
ly n
o re
-ad
just
men
ts.
A la
rge
num
ber
of o
ffic
es c
an b
e fi
tted
with
this
sys
tem
upo
n th
e sa
me
line,
and
thes
ear
e ad
vant
ages
whi
ch te
ndto
ret
ain
the
popu
lari
ty o
f th
is m
ode
ofsi
gnal
ling.
The
inst
rum
ent,
how
ever
, is
bein
g re
plac
ed b
y th
e so
unde
r w
here
ver
prac
ticab
le.
The
nam
e of
" s
ingl
e ne
edle
" is
giv
en to
this
inst
rum
ent a
s a
dist
inct
ion
from
the
obso
lete
sys
tem
of
" do
uble
-ne
edle
"w
orki
ng.
Alth
ough
the
syst
em n
eces
sita
tes
curr
ents
toei
ng s
ent t
o th
e lin
e in
bot
hdi
rect
ions
itis
ess
entia
lly w
orke
dup
on a
sin
gle
curr
ent p
rinc
iple
.It
mus
t not
, the
refo
re, b
e co
nfus
ed w
ith th
e w
ell-
know
n do
uble
curr
ent
syst
em.
NO
TE
S O
N T
EL
EG
RA
PHY
.85
CH
APT
ER
XI.
TH
E R
EL
AY
.
In th
e di
rect
sou
nder
sys
tem
the
inst
rum
ent f
rom
whi
ch th
e si
gnal
sar
e re
adis
act
uate
d by
a c
urre
nt p
assi
ng d
irec
t to
it fr
omth
e lin
e.T
his
arra
ngem
ent p
rodu
ces
very
sat
isfa
ctor
y re
sults
in th
e ca
se o
f ve
rysh
ort l
ines
, but
upo
n a
circ
uit o
f an
y co
nsid
erab
le le
ngth
the
" di
rect
"
syst
em b
ecom
es im
prac
ticab
le f
or m
any
reas
ons.
The
res
ista
nce
of a
long
cir
cuit
is o
f ne
cess
ity g
reat
, eve
n if
a w
ire
havi
ng a
com
para
tivel
yla
rge
area
of
cros
s se
ctio
n is
em
ploy
ed. T
he s
endi
ng b
atte
ry c
onse
quen
tlym
ust p
osse
ss a
hig
h vo
ltage
to p
rodu
ce a
cur
rent
of
suff
icie
nt s
tren
gth
to
actu
ate
a so
unde
r, b
ut b
eyon
d ce
rtai
n lim
its a
n in
crea
seof
bat
tery
pow
eris
not
pra
ctic
able
.A
gain
, the
cur
rent
rec
eive
d fr
om a
long
line
is s
ubje
ctto
con
side
rabl
e
vari
atio
ns in
str
engt
h.T
he in
sula
tion
resi
stan
ce o
f th
e lin
e fl
uctu
ates
with
var
ying
clim
atic
infl
uenc
es, a
nd th
e am
ount
of
curr
ent w
hich
leak
s
to e
arth
and
bec
omes
non
-ef
fect
ive
for
rece
ivin
g pu
rpos
es is
con
sequ
ently
a fa
ctor
to b
e re
ckon
ed w
ith.
Upo
n lo
ng li
nes
the
effe
ct o
f th
is lo
ss o
fcu
rren
t is
inte
nsif
ied,
as
ever
y po
int o
f su
ppor
t ope
ns u
p a
poss
ible
pat
hth
roug
h w
hich
a f
ract
ion
of th
e cu
rren
t may
esc
ape.
The
join
t res
ista
nce
form
ed b
y th
e nu
mer
ous
path
s of
leak
age
iste
rmed
the
" in
sula
tion
resi
stan
ce "
of
the
line,
and
dec
reas
es a
s th
e le
ngth
of th
e
circ
uit i
ncre
ases
.D
urin
g w
et w
eath
er it
will
be
obse
rved
that
the
amou
nt o
f cu
rren
t sen
t int
o a
circ
uit i
s ab
ove
the
norm
al, a
s th
ere
sulta
ntre
sist
ance
of
the
who
le li
no is
red
uced
by
the
fall
in in
sula
tion
resi
stan
ce.
The
am
ount
of
curr
ent r
ecei
ved,
how
ever
, is
less
than
the
norm
al, a
sth
eda
mp
cond
ition
of
the
supp
orts
aff
ords
gre
ater
fac
ilitie
sfo
r th
e es
cape
of
the
curr
ent.
It w
ill, t
here
fore
, be
seen
that
with
a m
inim
um w
orki
ngcu
rren
t of,
say
, 70
mill
iam
p6re
s di
rect
sou
nder
wor
king
bec
omes
impo
ssib
le,
exce
pt u
pon
very
sho
rt li
nes,
and
an
inst
rum
ent w
hich
will
be
actu
ated
by
am
uch
smal
ler
curr
ent i
s co
nseq
uent
ly in
trod
uced
.Su
ch a
n in
stru
men
t is
calle
d a
" re
lay,
" an
d ta
kes
the
plac
e of
the
soun
der
in th
e di
rect
soun
der
circ
uit.
The
inco
min
g cu
rren
t, al
thou
gh p
roba
bly
very
wea
k, a
ctua
tes
this
sen
sitiv
e in
stru
men
t, an
d by
its
effe
ct c
ause
s a
loca
l bat
tery
to b
e
join
ed u
p.T
he s
ound
er is
pla
ced
in th
e lo
cal b
atte
ry c
ircu
it, a
nd c
om-
para
tivel
y st
rong
cur
rent
s pa
ss th
roug
h th
eco
ils a
nd p
rodu
ce a
udib
lesi
gnal
s co
rres
pond
ing
with
the
curr
ents
rec
eive
d fr
omth
e lin
e.
TH
E P
OST
OFF
ICE
ST
AN
DA
RD
RE
LA
Y.
The
Pos
tO
ffic
eSt
anda
rd r
elay
isth
e in
stru
men
t use
d in
the
Bri
tish
Post
Off
ice.
Its
figu
re o
f m
erit
is h
alf
%m
illia
mpe
re a
nd th
is r
elay
90N
OT
ES
ON
TE
LE
GR
APH
Y.
rod
is f
ixed
at r
ight
angl
es.
At t
he e
nd o
f th
e ro
d is
a sm
all b
rass
knob
whi
ch b
eats
upon
a s
heet
of
met
al e
ach
time
the
arm
atur
e is
attr
acte
d. A
sha
rp m
etal
lic s
ound
is th
us e
mitt
ed a
s th
ere
sult
of e
ach
sign
al b
eing
rec
eive
d.T
he s
ound
upon
the
righ
t-ha
nd "
bel
l," a
s it
iste
rmed
, is
diss
imila
r in
tone
fro
m th
atup
on th
e le
ft-h
and
bell,
and
, con
-se
quen
tly, t
he s
igna
ls c
an b
eea
sily
rea
d by
sou
nd, w
hile
the
send
ing
port
ion
is ju
st a
s si
mpl
e to
man
ipul
ate
as th
at u
sed
with
the
sing
lene
edle
inst
rum
ent.
Whe
nse
ndin
g, th
e re
lay
and
loca
l cir
cuit
are
Cut
out
,a
" si
ngle
cur
rent
" g
alva
nom
eter
only
, or,
mor
e st
rict
ly s
peak
ing,
aga
lvan
osco
pe, b
eing
in th
at p
art o
f th
e ci
rcui
tw
ith th
e co
mm
utat
or a
ndm
ain
batte
ry.
The
tapp
ers
are
join
edup
so
as to
pre
vent
sho
rt-c
ircu
iting
ofth
e se
ndin
g ba
ttery
sho
uld
both
be
sim
ulta
neou
sly
depr
esse
d.W
hen
a cu
rren
t is
rece
ived
fro
mth
e do
wn
line
itpa
sses
thro
ugh
the
galv
anom
eter
, the
nce
to th
e br
ass
conn
ectio
nup
on th
e lo
wer
sid
e of
the
left
-han
d ta
pper
, thr
ough
the
wir
ejo
ined
to th
e le
ft-h
and
term
inal
fro
mw
hich
the
stra
p ha
s be
enre
mov
ed, a
nd th
roug
h th
ere
lay
coils
fro
m"
righ
t " to
" le
ft."
It th
en p
asse
s to
the
righ
t-ha
nd te
rmin
al o
f th
eco
mm
utat
or, t
hrou
gh th
e br
ass
conn
ectio
nup
on th
e un
der
side
of
the
righ
t-ha
nd ta
pper
, and
then
ce to
ear
th.
A c
urre
nt r
ecei
ved
inan
opp
osite
dire
ctio
n, i.
e., o
ne a
ssum
ed to
com
e in
at t
he "
eart
h "
conn
ectio
n,m
ay b
etr
aced
sim
ilarl
y, th
roug
h th
esa
me
path
in a
n op
posi
te d
irec
tion,
and
itpa
sses
thro
ugh
the
rela
y co
ils f
rom
"lo
ft "
to "
righ
t." I
n th
e fo
rmer
cas
eth
e co
ntac
t ton
gue
is d
raw
n to
the
righ
t-ha
nd c
onta
ct p
oint
, whi
chm
ovem
ent o
pera
tes
the
loca
l bat
tery
and
the
righ
t-ha
nd b
ell.
In th
ela
tter
case
exa
ctly
the
reve
rse
cond
ition
sar
e br
ough
t abo
ut.
The
tong
ueof
the
rela
y m
oves
to th
e le
ft-h
and
cont
act
scre
w a
nd jo
ins
up th
e le
ft-
hand
bol
l.B
y th
us r
ever
sing
the
dire
ctio
n of
the
rece
ived
cur
rent
by
mea
ns o
f th
e co
mm
utat
or a
t the
dis
tant
sta
tion,
a ve
ry s
impl
e m
etho
d of
soun
d re
adin
g is
est
ablis
hed.
The
coi
ls o
f th
e so
unde
rar
e sh
unte
d to
dest
roy
the
ill-e
ffec
ts o
f se
lf-i
nduc
tion
upon
the
rela
y co
ntac
t poi
nts.
Acu
rren
t str
engt
h of
abo
ut 2
0 m
illia
mpe
res
ispr
ovid
ed u
pon
this
sys
tem
,w
hich
has
the
adva
ntag
e of
a s
ensi
tive
rela
y as
the
rece
ivin
g in
stru
men
t,an
d of
bei
ng a
qui
cker
met
hod
ofsi
gnal
ling
than
the
sing
le n
eedl
esy
stem
.E
LE
CT
RO
-MA
GN
ET
IC I
ND
UC
TIO
N.
Eve
ry w
ire
carr
ying
a c
urre
nt p
osse
sses
a m
agne
ticfi
eld;
the
lines
of
forc
e, o
r lin
es o
f in
duct
ion,
sur
roun
d th
e w
ire
alon
g its
who
le le
ngth
inth
e fo
rm o
f co
ncen
tric
cir
cles
, the
wir
e its
elf be
ing
thei
r co
mm
on c
entr
e.W
hen
a cu
rren
t is
star
ted
the
lines
of
forc
esp
ring
into
exi
sten
ce, a
nd it
may
be
said
that
they
rad
iate
in a
n ou
twar
d di
rect
ion
from
the
wir
e.W
ith a
n in
crea
se in
the
stre
ngth
of
the
curr
ent t
hem
agne
tic f
ield
bec
omes
exte
nded
, and
a f
urth
er r
adia
tion
take
s pl
ace.
A d
imin
utio
n of
the
curr
ent s
tren
gth
caus
es a
par
tial c
olh.
ile o
f th
em
agne
tic f
ield
, the
ten-
denc
y be
ing
for
the
lines
of
forc
e to
rec
ede
into
the
wir
e.A
t the
ces
satio
n
NO
TE
S O
N T
EL
EG
RA
PHY
.91
of th
e cu
rren
t the
mag
netic
fie
ld c
olla
pses
and
the
lines
of
forc
e re
turn
toth
e w
ire
from
whi
ch th
ey s
prun
g.
Whe
n a
cond
ucto
r is
cut
by
a lin
e of
for
ce, o
r w
hen
a lin
e of
for
ce is
cut
by a
con
duct
or, a
n el
ectr
o-m
otiv
e fo
rce
is s
et u
p, a
nd, i
fth
e co
nduc
tor
form
s pa
r of
a c
lose
d ci
rcui
t, a
curr
ent w
ill f
low
thro
ugh
that
cir
cuit.
The
dir
ectio
n in
whi
ch th
e cu
rren
t will
flo
w is
det
erm
ined
by
the
dire
ctio
nin
whi
ch th
e lin
es o
f fo
rce
cut t
hrou
gh th
e co
nduc
tor.
For
inst
ance
,su
ppos
e th
at tw
o w
ires
AB
and
CD
run
par
alle
l and
in c
lose
pro
xim
ity to
each
oth
er, a
nd th
at a
curr
ent
isst
arte
din
the
form
erin
a
FIG
. 47.
dire
ctio
n fr
om B
toA
(Fig
.47
).T
helin
osof
forc
ede
velo
ped
radi
ate
outw
ards
fro
mth
e w
ire.
Som
e of
thes
e lin
es o
f fo
rce
cut
thro
ugh
CD
tran
sver
sely
and
prod
uce
anel
ectr
o-m
otiv
efo
rce
whi
ch c
ause
s a
mom
enta
ry c
urre
nt to
flo
w f
rom
C to
D. A
n in
crea
seof
the
curr
ent s
tren
gth
in A
B w
ill c
ause
a f
urth
er r
adia
tion
of th
e lin
es o
ffo
rce
and
anot
her
mom
enta
ry c
urre
ntw
ill f
low
thro
ugh
CD
.T
hese
mom
enta
ry c
urra
nts
will
flo
w in
an
oppo
site
dir
ectio
n to
the
orig
inal
cur
-re
nt. B
y a
dim
inut
ion
of th
e st
reng
th o
f th
e cu
rren
t the
mag
netic
fie
ld w
illpa
rtia
lly c
olla
pse,
and
the
lines
of
forc
e w
ill c
ut th
roug
h C
D in
a r
ever
sedi
rect
ion
as th
ey p
ass
inw
ards
tow
ards
AB
.T
he m
omen
tary
indu
ced
curr
ent i
n C
D w
ill n
ow b
e in
the
sam
e di
rect
ion
as th
e or
igin
al c
urre
nt,
and,
obv
ious
ly, w
ith th
e ce
ssat
ion
of th
e la
tter
and
the
cons
eque
nt to
tal
colla
pse
of th
e m
agne
tic f
ield
, the
fur
ther
indu
ced
curr
ent w
ill a
lso
flow
from
D to
C.
SEL
F-IN
DU
CT
ION
.
Whe
n a
wir
e is
wou
nd in
to a
coi
l, or
spi
ral,
the
effe
cts
of e
lect
ro-
mag
netic
indu
ctio
n ar
e in
tens
ifie
d.T
he li
nes
of f
orce
, at t
heir
cre
atio
n,cu
t thr
ough
eac
h ad
jace
nt c
onvo
lutio
n of
the
wir
e an
d in
duce
a m
omen
tary
curr
ent w
hich
opp
oses
the
orig
inal
cur
rent
, and
pre
vent
s th
e la
tter
from
imm
edia
tely
ris
ing
to it
s m
axim
um s
tren
gth
(Fig
. 48)
.T
his
mom
enta
rycu
rren
t is
term
ed a
n ex
tra
-cur
rent
inve
rse.
Whe
n th
e ba
ttery
cir
cuit
isbr
oken
and
the
lines
of
forc
e co
llaps
e, th
e in
duce
d cu
rren
t fol
low
s th
epr
imar
y cu
rren
t, te
ndin
g to
pro
long
it a
nd r
etar
d its
pro
mpt
dis
appe
aran
ce.
Thi
s is
term
ed th
e ex
tra
curr
ent d
irec
t.
If a
sof
t iro
n co
re is
intr
oduc
ed in
to th
e co
il th
e ef
fect
s of
" s
elf-
indu
ctio
n "
are
incr
ease
d be
caus
e th
e lin
es o
f fo
rce
are
mor
e nu
mer
ous.
As
the
elec
tro-
mot
ive
forc
e of
the
indu
ced
curr
ents
dep
ends
upo
n th
e
88N
OT
ES
ON
TE
LE
GR
APH
Y.
inst
rum
ent.
Whe
n th
e to
ngue
s ar
e ne
arer
to th
e po
le-p
iece
s up
on o
nesi
de th
an to
thos
e up
on th
e ot
her
the
attr
actio
n w
ill b
e to
war
ds th
ene
arer
and
the
adju
stm
ent i
s sa
id to
hav
e a
" bi
as."
To
be in
its
mos
t sen
sitiv
eco
nditi
on, h
owev
er, t
he in
stru
men
t sho
uld
be a
djus
ted
so th
at th
e to
ngue
sre
mai
n on
the
side
upo
n w
hich
they
are
pla
ced.
For
soun
der
wor
king
the
rela
y is
adj
uste
d so
that
it h
as a
slig
ht b
ias
to th
e sp
acin
g si
de, a
nd th
ete
rmin
al m
arke
d S
is le
ft d
isco
nnec
ted.
Fig.
45
show
s a
sing
le c
urre
nt s
ound
er c
ircu
it w
orke
d by
mea
ns o
fa
rela
y, a
nd it
will
be
seen
that
the
rela
y is
the
actu
al r
ecei
ving
inst
rum
ent,
whi
le th
e so
unde
r or
rea
ding
inst
rum
ent i
s si
mpl
y un
der
its c
ontr
ol.
NO
TE
S O
N T
EL
EG
RA
PHY
.89
CH
APT
ER
XII
.
TH
E D
OU
BL
E P
LA
TE
SO
UN
DE
R.
The
" s
endi
ng "
par
t of
this
sys
tem
is a
com
mut
ator
ver
y si
mila
r to
that
used
with
the
sing
le n
eedl
e, a
nd th
e m
etho
d of
sig
nalli
ng is
iden
tical
inea
ch c
ase.
The
re is
a s
light
alte
ratio
n in
the
conn
ectio
ns o
f th
e do
uble
plat
e so
unde
r, th
e m
etal
str
ap a
t the
bac
k of
the
com
mut
ator
bei
ngre
mov
ed a
nd th
e tw
o te
rmin
als
join
ed s
epar
atel
y to
a r
elay
(Fi
g. 4
6),
whi
ch is
the
actu
al r
ecei
ving
inst
rum
ent.
The
rel
ay to
ngue
s ar
e se
t
,..1-
31":
Up
Lif
esor
Ear
4
FIG
,16.
neut
ral b
y th
e or
dina
ry m
eans
of
adju
stm
ent,
but t
he c
onta
ct to
ngue
isno
rmal
ly h
eld
mid
way
bet
wee
n th
e co
ntac
t poi
nts
by m
eans
of
two
anta
goni
stic
spr
ings
.T
he lo
cal b
atte
ry c
ircu
it is
in tw
o se
ctio
ns, a
nd it
depe
nds
upon
the
dire
ctio
nof
the
rece
ived
cur
rent
thro
ugh
the
rela
y w
heth
er th
eri
ght
orth
ele
ft-h
and
sect
ion
isjo
ined
up.
In e
ach
sect
ion
ofth
elo
cal
batte
ryci
rcui
tis
asi
mpl
y -d
evis
edso
unde
r or
ele
ctro
-mag
net,
to th
e ar
mat
ure
of w
hich
a s
mal
l met
al
94N
OT
ES
ON
TE
LE
GR
APH
Y.
rece
ivin
g st
atio
n, a
nd it
'will
be
appa
rent
that
whe
n si
gnal
s of
sho
rt d
ura
tion
are
requ
ired
to f
ollo
w e
ach
othe
r in
rap
id s
ucce
ssio
n, s
ome
met
hod
ofcl
eari
ng th
e lin
e m
ust b
e ad
opte
d in
ord
er th
atdi
stor
tion
may
be
prev
ente
d....
The
dif
ficu
lty is
pra
ctic
ally
ove
rcom
e by
intr
oduc
ing
a do
uble
-cu
rren
t sys
tem
. Bet
wee
n ea
ch s
igna
l a c
urre
nt in
an
oppo
site
dir
ectio
n to
that
req
uire
d to
pro
duce
a m
arki
ng e
ffec
tup
on th
e re
lay
is s
ent
tolin
e, a
nd th
is c
lear
s th
e lin
e of
the
reta
ined
cha
rges
by
the
act o
fne
utra
lisat
ion.
The
se n
eutr
alis
ing
curr
ents
are
term
ed "
spa
cing
" c
ur-
rent
s to
dis
tingu
ish
them
fro
m th
e or
dina
ry "
mar
king
" cu
rren
ts f
rom
FIG
49
whi
ch th
e re
adab
le s
igna
ls r
esul
t.N
ot o
nly
does
the
doub
le c
urre
ntsy
stem
qui
cken
the
rate
of
wor
king
in th
e m
anne
r de
scri
bed,
but
the
rela
ym
ay b
e w
orke
d in
its
mos
t sen
sitiv
e co
nditi
on, i
.e.,
with
out b
ias,
as
the
" sp
acin
g "
curr
ent c
ause
s th
e to
ngue
s of
,. th
e re
lay
to r
esum
e th
eir
norm
al p
ositi
on a
fter
eac
h si
gnal
.It
will
al
'be
notic
ed th
at f
or o
rdin
ary
soun
der
wor
king
an
anta
goni
stic
spr
ing
is n
ot n
eede
d.In
pra
ctic
e, h
ow-
ever
, a s
light
spa
cing
bia
s is
giv
en th
e re
lay
in o
rder
that
the
loca
l bat
tery
circ
uit m
ay n
ot b
e cl
osed
whe
n no
cur
rent
is b
eing
rec
eive
d fr
om th
e lin
e.A
noth
er a
dvan
tage
of
this
sys
tem
is th
atth
e ra
pid
and
cons
tant
lyre
vers
ing
curr
ents
pre
vent
the
deve
lopm
ent o
f re
sidu
al m
agne
tism
in th
e
NO
TE
S O
N T
EL
EG
RA
PHY
.95
core
s of
the
rela
y; b
ut a
dis
adva
ntag
e is
that
the
batte
ry is
wor
ked
twic
eas
har
d as
in th
e si
ngle
cur
rent
sys
tem
.W
hen
circ
uits
are
wor
ked
upon
the
doub
le c
urre
nt p
rinc
iple
a s
peci
ally
devi
sed
key
is e
mpl
oyed
to s
end
a sp
acin
g cu
rren
t aut
omat
ical
ly a
fter
eac
hm
arki
ng c
urre
nt.
Thi
s is
don
e ea
ch ti
me
the
key
is a
llow
ed to
res
ume
its p
ositi
on o
f re
st.
By
mea
ns o
f a
switc
h th
e ba
ttery
is d
isco
nnec
ted
atw
ill, a
nd th
e re
ceiv
ing
inst
rum
ent i
s th
en jo
ined
to th
e lin
e.T
he le
ver
is d
ivid
ed in
to tw
o pa
rts,
whi
ch a
re s
epar
ated
fro
m e
ach
othe
rby
a s
trip
of
insu
latin
g m
ater
ial s
uch
as e
boni
te.
It p
lays
bet
wee
n fo
ur
SP
AC
E.
FIG
.50
cont
act s
prin
gs, a
nd th
e m
etal
lic s
ectio
ns m
ake
cont
act w
ith th
e tw
olo
wer
spr
ings
whe
n th
e le
ver
is a
t res
t, an
d w
ith th
e up
per
ones
whe
n it
isde
pres
sed.
Fig.
49
show
s th
e in
tern
al c
onne
ctio
ns o
f a
five
-te
rmin
al d
oubl
e cu
rren
tke
y, a
nd F
ig. 5
0 in
dica
tes
the
cond
ition
s ex
istin
g w
hen
(1)
a sp
acin
gcu
rren
t is
bein
g se
nt to
line
;(2
) w
hen
the
key
is d
epre
ssed
and
a m
arki
ngcu
rren
t is
bein
g se
nt ;
(3)
whe
n th
e sw
itch
isto
" r
ecei
ve "
;in
oth
erw
ords
, whe
n th
e lin
e is
join
ed to
the
rece
ivin
g ap
para
tus.
A k
ey h
avin
g on
ly f
our
term
inal
s is
use
d in
the
" un
iver
sal b
atte
rysy
stem
" o
f w
orki
ng, a
nd a
des
crip
tion
of it
will
be
give
n w
hen
deal
ing
with
that
sub
ject
at a
late
r pe
riod
.
92N
OT
ES
ON
TE
LE
GR
APH
Y.
num
ber
of li
nes
of f
orce
whi
ch c
ut th
roug
ha
cond
ucto
r an
d al
so u
pon
the
rate
at w
hich
they
cut
it, t
he s
udde
n ce
ssat
ion
or v
aria
tion
of a
cur
rent
pass
ing
thro
ugh
the
coil
of a
n el
ectr
o-m
agne
t, w
hich
is w
ound
with
man
ytu
rns
offi
ne w
ire,
will
prod
uce
a ve
ry h
igh
indu
ced
elec
tro-
mot
ive
forc
e.co
nseq
uent
ly s
elf-
indu
ctio
n, in
thes
e ci
rcum
stan
ces,
is s
aid
to b
eco
mpa
rativ
ely
grea
t.
F1G
. 48.
Self
-ind
uctio
n is
som
etim
es c
alle
d "
spur
ious
res
ista
nce,
"on
acc
oun
tof
its
reta
rdin
g ef
fect
upo
n th
e pr
imar
y cu
rren
t.It
s un
it is
term
ed th
e"
Hen
ry "
or
" Se
ccoh
m."
It w
ill n
ow b
e ne
cess
ary
to c
onsi
der
the
effe
cts
of s
elf-
indu
ctio
nin
conn
ectio
n w
ith a
cir
cuit
such
as
that
for
min
g th
e lo
cal c
ircu
it of
the
doub
le p
late
sou
nder
sys
tem
.B
y th
e ac
tion
of th
e pr
imar
y cu
rren
tpa
ssin
g th
roug
h th
e co
ils o
f th
e re
lay
the
loca
l cir
cuit
is c
lose
d an
d its
batte
ry jo
ined
up,
and
, as
a co
nseq
uenc
e, a
com
para
tivel
y st
rong
cur
rent
pass
es th
roug
h th
e el
ectr
o-m
agne
t, or
sou
nder
, coi
ls.
Whe
n th
e re
lay
tong
ue r
esum
es it
s no
rmal
pos
ition
by
the
cess
atio
n of
the
prim
ary
or li
necu
rren
t,th
elo
cal
circ
uit
isdi
scon
nect
ed,
but
a hi
gh in
duce
del
ectr
o-m
otiv
efo
rce
isse
tup
in th
eco
ilsof
the
soun
der.
The
tong
ue o
f th
e re
lay
is s
epar
ated
fro
m th
e co
ntac
t scr
ews
by a
sm
all
air
gap;
but
the
indu
ced
elec
tro-
mot
ive
forc
e in
the
soun
der
coils
will
prob
ably
be
suff
icie
ntly
hig
h as
to p
rodu
ce a
cur
rent
cap
able
of
brid
ging
acro
ss th
e ai
r sp
ace,
and
cau
se a
spa
rk to
pas
s.T
he e
ffec
t of
this
spa
rkw
ill b
e to
cor
rode
the
cont
act p
oint
s, a
nd u
ltim
atel
y to
dest
roy
the
met
allic
con
nect
ion
nece
ssar
y fo
r th
e fr
eepa
ssag
e of
the
curr
ent t
hrou
ghth
e lo
cal c
ircu
it.
To
prev
ent s
uch
dam
age
a sh
unt i
s jo
ined
curr
ent,th
e te
rmin
als
of th
eso
unde
r co
ils, a
nd th
e m
omen
tary
indu
cea
or r
athe
r th
e ex
tra
curr
ent d
irec
t, ci
rcul
ates
thro
ugh
the
shun
t rat
her
than
pass
acr
oss
the
air
gap
at th
e re
lay
cont
act p
oint
s.
NO
TE
S O
N T
EL
EG
RA
PHY
.93
CH
APT
ER
XII
I.
DO
UB
LE
CU
RR
EN
T W
OR
KIN
G.
The
sin
gle
curr
ent s
yste
m, a
lrea
dy d
escr
ibed
, can
be
empl
oyed
onl
y up
onci
rcui
ts o
f co
mpa
rativ
ely
shor
t len
gths
, eve
n w
hen
a re
lay
is in
trod
uced
.A
cur
rent
sen
t int
o a
line
" ch
arge
s "
it ;
the
char
ge a
cts
indu
ctiv
ely
upon
the
eart
h an
d ne
ighb
ouri
ng o
bjec
ts a
nd p
rodu
ces
indu
ced
char
ges
upon
them
.T
he in
duce
d ch
arge
s, in
turn
, rea
ct u
pon
the
wir
e, a
nd th
ere
actio
ns c
ause
a p
ortio
n of
the
orig
inal
cha
rge
to b
e he
ld b
ound
.T
hew
ire,
as
a co
nseq
uenc
e, is
sai
d to
pos
sess
a s
tatic
cha
rge.
The
am
ount
of
elec
tric
ity th
us h
eld
depe
nds
upon
the
dim
ensi
ons
of th
e w
ire,
bot
h as
rega
rds
its le
ngth
and
thic
knes
s, o
r di
amet
er, a
nd a
lso
upon
its
prox
imity
to th
e ea
rth
and
adja
cent
con
duct
ors.
The
pro
pert
y po
sses
sed
by a
cond
ucto
r of
ret
aini
ng a
cha
rge
is te
rmed
ele
ctro
-sta
tic c
apac
ity, a
ndth
is c
apac
ity h
as to
be
satis
fied
bef
ore
a cu
rren
t, an
d co
nseq
uent
ly a
sig
nal,
can
reac
h th
e di
stan
t end
of
the
line.
As
the
initi
al p
ortio
n of
the
char
ge is
abso
rbed
in s
atis
fyin
g th
e ca
paci
ty o
f th
e lin
e, th
e co
nseq
uent
eff
ect u
pon
asi
gnal
is to
ret
ard
its a
ppea
ranc
e at
the
rece
ivin
g of
fice
, and
the
rate
of
wor
king
is th
eref
ore
kept
ver
y lo
w.
Upo
n sh
ort a
eria
l lin
es th
e ef
fect
s of
elec
tro-
stat
ic c
apac
ity a
re n
eglig
ible
, but
upo
n lo
ng w
ires
and
und
er-
grou
nd a
nd s
ubm
arin
e ca
bles
they
are
ver
y pr
onou
nced
.O
n ac
coun
t of
the
insu
latin
g m
ater
ial w
ith w
hich
the
last
two
nam
ed a
re s
urro
unde
dbe
ing
supe
rior
to a
ir a
s an
indu
ctiv
e m
ediu
m, t
he c
apac
ity o
f su
ch c
ircu
its is
very
gre
at.
The
pro
pert
y po
sses
sed
by d
i-el
ectr
ics,
suc
h as
gut
ta-p
erch
a,pa
raff
in,
etc.
,of
allo
win
g in
duct
ion
tota
kepl
ace
acro
ssth
emis
term
edth
eir
" sp
ecif
icin
duct
ive
capa
city
," a
ndth
eco
mpa
riso
ndr
awn
isbe
twee
nth
atof
any
part
icul
ardi
-el
ectr
ican
dai
r.T
hus
ifgu
tta-p
erch
aw
ere
subs
titut
edfo
rai
r,an
dal
lot
her
cond
ition
s re
mai
ned
undi
stur
bed,
the
capa
city
of
a co
nduc
tor
wou
ldbe
incr
ease
dto
rath
er m
ore
than
fou
r tim
es it
s ca
paci
tyin
air.
Gut
ta-p
erch
a is
ver
y la
rgel
y us
ed a
s an
insu
lato
r fo
r un
derg
roun
d an
d su
b-m
arin
e lin
es, a
nd, a
s a
cons
eque
nce,
the
elec
tro-
stat
ic c
apac
ity o
f th
ese
circ
uits
is c
onsi
dera
ble.
Aga
in, a
s in
duct
ion
take
s pl
ace
acro
ss a
com
para
-tiv
ely
shor
t dis
tanc
e, o
win
g to
the
cont
igui
ty o
f th
e ea
rth
and
othe
r co
n-du
ctor
s, th
e el
ectr
o-st
atic
eff
ects
are
stil
l fur
ther
inte
nsif
ied.
Whe
n th
e ba
ttery
fro
m w
hich
the
curr
ent e
man
ates
is c
ut o
ff, t
he s
tatic
char
ge, r
etai
ned
by th
e w
ire,
esc
apes
to e
arth
by
the
shor
test
pos
sibl
e ro
ute.
If th
e ci
rcui
t is
impe
rfec
tly in
sula
ted
as m
ost r
enal
line
s ar
e, o
win
g to
am
oist
atm
osph
ere,
etc
., a
port
ion
of th
e di
scha
rge
take
s pl
ace
thro
ugh
the
path
s of
leak
age,
but
the
rem
aind
er p
asse
s ou
t at t
he e
arth
-co
nnec
ted
ends
of
the
line.
The
eff
ect u
pon
the
curr
ent i
sto
und
uly
prol
ong
it at
the
98N
OT
ES
ON
TE
LE
GR
APH
Y.
curr
ent p
assi
ng th
roug
h on
ly o
ne c
oil i
s sh
own
diag
ram
atic
ally
in F
igs.
53
and
54, a
nd in
bot
h ca
ses
" m
arki
ng "
eff
ects
res
ult f
rom
the
curr
ents
trav
ersi
ng th
e pa
ths
indi
cate
d in
the
dire
ctio
ns s
how
n by
the
arro
ws.
Dup
lex
wor
king
may
be
arra
nged
eith
er u
pon
the
sing
le c
urre
nt o
r th
edo
uble
cur
rent
sys
tem
.It
is r
arel
y ne
cess
ary
to w
ork
any
circ
uit d
uple
xco
ntin
ually
, the
refo
re a
six
term
inal
two-
way
sw
itch
is u
sed,
and
by
itsm
eans
a s
impl
ex c
ircu
it m
ay b
e re
adily
con
vert
ed in
to a
dup
lex
circ
uit.
Bef
ore
dupl
ex w
orki
ng c
omm
ence
s it
is n
eces
sary
for
eac
h st
atio
n to
bal
ance
its a
rtif
icia
l cir
cuit
agai
nst t
he li
ne c
ircu
it, s
o th
at th
e cu
rren
tm
ay s
plit
equa
lly b
etw
een
the
two
sect
ions
.
TH
E S
ING
LE
CU
RR
EN
T D
UPL
EX
SY
STE
M.
The
sw
itch
at e
ach
offi
ce is
turn
ed to
" d
uple
x,"
and,
by
depr
essi
ng th
eke
y se
para
tely
at e
ither
sta
tion,
it m
ay b
e as
cert
aine
d w
hen
suff
icie
ntre
sist
ance
has
bee
n in
sert
ed in
the
set o
f re
sist
ance
coi
ls, o
r rh
eost
at, t
oef
fect
a b
alan
ce o
f th
e re
sist
ance
of
the
line
and
that
par
t of
the
dist
ant
stat
ion'
s ap
para
tus
dire
ctly
in th
e lin
e ci
rcui
t.T
his
is d
eter
min
ed b
yob
serv
ing
whe
n th
e ne
edle
of
the
diff
eren
tially
-w
ound
gal
vano
met
er is
unaf
fect
ed b
y th
e pa
ssag
e of
the
curr
ent t
hrou
gh th
e co
ils, f
or, i
f th
e tw
oeq
ual p
ortio
ns o
f th
e di
vide
d cu
rren
t pas
s th
roug
h th
em in
opp
osite
dir
ec-
tions
, the
indu
ced
mag
net w
ill n
ot b
e de
flec
ted.
In
the
sing
le c
urre
nt d
uple
xsy
stem
the
galv
anom
eter
nee
dle
rem
ains
ver
tical
and
per
fect
ly s
tead
y w
hen
the
key
is d
epre
ssed
. The
dif
fere
ntia
l gal
vano
met
er is
iden
tical
in c
onst
ruct
ion
with
the
Spag
nole
tti n
eedl
e al
read
y de
scri
bed,
with
the
exce
ptio
n th
at th
eco
ils a
re d
iffe
rent
ially
wou
nd a
nd jo
ined
up
inse
ries
.T
his
met
hod
ofw
indi
ng is
inva
riab
ly a
dopt
ed f
or d
uple
x w
orki
ng, b
ut th
e ga
lvan
omet
erm
ay b
e jo
ined
up
in "
ser
ies
" or
in "
qua
ntity
" a
s ne
cess
ity r
equi
res.
Dif
fere
ntia
l win
ding
is r
esor
ted
to in
ord
er th
at th
e di
ffer
ence
bet
wee
n, o
rth
e eq
ualit
y of
, the
str
engt
hs o
f cu
rren
ts p
assi
ng in
opp
osite
dir
ectio
nsth
roug
h th
e co
ils m
ay b
e ob
serv
ed.
The
rhe
osta
t in
gene
ral u
se c
onsi
sts
of a
num
ber
of r
esis
tanc
e co
ils s
oco
nnec
ted
that
, by
the
rota
tion
of tw
o ar
ms
over
a n
umbe
r of
con
tact
poin
ts, a
s m
any
of th
e co
ils a
s ar
e re
quir
ed c
an b
e re
adily
bro
ught
into
use.
The
con
tact
poi
nts,
bet
wee
n w
hich
the
coils
are
fitt
ed, a
re a
rran
ged
upon
a c
ircu
lar
dial
, one
-hal
f of
thei
r nu
mbe
r be
ing
used
in c
onne
ctio
nw
ith o
ne a
rm a
nd th
e ot
her
half
with
the
othe
r ar
m.
The
set
of
coils
isdi
vide
d in
to tw
o se
ctio
ns.
The
one
con
sist
s of
ten
coils
, eac
h of
40
ohm
sre
sist
ance
, and
the
othe
r of
a s
imila
r nu
mbe
r of
coi
ls, e
ach
havi
ng a
val
ueof
400
ohm
s.C
onne
ctio
n be
twee
n th
e tw
o se
ctio
ns is
mad
e by
mea
ns o
fth
e ar
ms
and
cont
act p
oint
s, a
nd th
e co
ils a
re a
rran
ged
so th
at a
nyre
sist
ance
up
to 4
,400
ohm
s, b
y gr
adat
ions
of
40 o
hms,
may
be
obta
ined
by
the
man
ipul
atio
n of
the
revo
lvin
g ar
ms.
NO
TE
S O
N T
EL
EG
RA
PHY
.99
Thr
oe o
ther
res
ista
nce
coils
hav
ing
valu
es o
f 10
, 20,
and
4,0
00 o
hms
resp
ectiv
ely
are
fitte
d to
the
rheo
stat
, but
thes
e ar
e in
depe
nden
t of
the
111'
1111
4.T
hey
can
be u
sed,
how
ever
, in
conj
unct
ion
with
the
40 a
nd 4
0011
1110
13 c
oils
, and
the
rang
e of
the
set i
s en
larg
ed b
y th
eir
addi
tion
to 8
,430
ohm
s, a
ny m
ultip
le o
f 10
ohm
s up
to th
at v
alue
bei
ng o
btai
nabl
e.T
hese
extr
a co
ils a
re b
roug
ht in
to u
se b
y th
e w
ithdr
awal
of
coni
cal b
rass
plu
gs, i
na
sim
ilar
man
ner
to th
at d
escr
ibed
in c
onne
ctio
n w
ith "
res
ista
nce
coils
."ri
g. 5
5 sh
ows
how
the
coils
of
a rh
eost
at m
ay b
e co
nnec
ted
betw
een
the
two
term
inal
s.
The
con
nect
ions
of
a si
ngle
cur
rent
cir
cuit
arra
nged
for
dup
lex
wor
king
are
show
n in
Fig
. 66
;th
e ap
para
tus
not e
ssen
tial t
o a
theo
retic
al e
xpla
na-
tion
of th
e sy
stem
bei
ng o
mitt
ed. Fi
g ,5
5.
The
re a
re th
ree
cond
ition
s w
hich
hav
e to
be
met
in o
rder
that
dup
lex
wor
king
may
be
esta
blis
hed,
viz
. :-
1. W
ith o
ne k
ey o
nly
depr
esse
d a
" m
arki
ng "
eff
ect s
houl
d be
pro
-du
ced
in th
e re
lay
at th
e op
posi
te e
nd o
f th
e lin
e.
2. W
ith b
oth
keys
dep
ress
ed a
t the
sam
e tim
e a
" m
arki
ng "
effe
ctsh
ould
be
prod
uced
in th
e re
lay
at b
oth
ends
of
the
line.
9. W
ith o
ne k
ey d
epre
ssed
and
the
othe
r in
an
inte
rmed
iate
pos
ition
,L
e., w
hen
the
leve
r is
in c
onta
ct w
ith n
eith
er th
e ba
ck n
or th
e fr
ont s
top,
a "
mar
king
" e
ffec
t sho
uld
be p
rodu
ced
at th
e of
fice
whe
re th
e la
tter
con-
ditio
n ex
ists
.
It s
houl
d be
men
tione
d he
re th
at b
oth
rela
ys a
re a
djus
ted
to h
ave
a',l
ight
spa
cing
bia
s, s
o th
at th
elo
cal c
ircu
its m
ay n
otbe
join
ed
2p;
100
NO
TE
S O
N T
EL
EG
RA
PHY
.
upex
cept
whe
nth
ecu
rren
ts p
rodu
cem
arki
ngef
fect
s up
on th
ere
lays
.It
sho
uld
also
be
born
e in
min
d th
at a
s th
e "
eart
h "
retu
rn h
asno
res
ista
nce
the
two
eart
h co
nnec
tions
, one
at e
ach
end
of th
e ci
rcui
t, ar
epr
actic
ally
join
ed to
geth
er, a
nd a
cur
rent
pas
sing
to e
arth
at o
ne o
ffic
e is
assu
med
to c
ome
in a
t the
ear
th c
onne
ctio
n of
the
othe
r.
Con
side
r th
e fi
rst c
ondi
tion
in c
onju
nctio
n w
ith F
ig. 5
6, a
nd a
ssum
eth
at th
e ke
y at
the
" up
" s
tatio
n is
dep
ress
ed.
The
cur
rent
fro
m th
eba
ttery
at t
hat o
ffic
e pa
sses
to th
e ga
lvan
omet
er, a
nd d
ivid
es e
qual
lybe
twee
n th
e ar
tific
ial a
nd li
ne c
ircu
its.
Tha
t whi
ch p
asse
s th
roug
h th
ear
tific
ial c
ircu
it ar
rive
s at
the
batte
ry v
ia th
e D
-U
coi
l of
the
rela
y.T
heot
her
half
of
the
curr
ent,
whi
ch p
asse
s to
line
, arr
ives
at t
he U
-ci
rcle
term
inal
of
the
" do
wn"
off
ice
rela
y.A
fter
pas
sing
thro
ugh
the
U -
circ
leD
-ci
rcle
coi
l, th
e re
sist
ance
blo
ck r
,th
e ba
ck s
top
of th
e ke
y an
d on
eco
il of
the
galv
anom
eter
, it t
hen
find
s "
eart
h."
It m
ust n
ow b
e as
sum
ed
FIG
56
to h
ave
arri
ved
at th
e U
-ci
rcle
term
inal
of
the
" up
" s
tatio
n's
rela
y, a
ndits
pat
h is
thro
ugh
the
U -
circ
le D
-ci
rcle
coi
l, an
d th
ence
to th
e ba
ttery
from
whi
ch it
em
anat
ed.
The
eff
ect o
f th
ese
curr
ents
upo
n th
e ap
para
tus
mus
t now
be
cons
ider
ed.
The
gal
vano
met
er a
t the
" u
p "
stat
ion
is n
ot d
efle
cted
, as
equa
l cur
rent
spa
ss th
roug
h th
e tw
o se
ctio
ns o
f th
e co
ils in
opp
osite
dir
ectio
ns.
The
rela
y at
this
off
ice
is a
lso
unaf
fect
ed, f
or th
e ef
fect
of
the
curr
ent p
assi
ngth
roug
h th
e D
-U
coi
l fro
m th
e ar
tific
ial c
ircu
it is
neu
tral
ised
by
the
effe
ctof
the
line
curr
ent p
assi
ng th
roug
h th
e U
-ci
rcle
D -
circ
le c
oil.
The
two
curr
ents
pas
s th
roug
h th
e re
lay
coils
in o
ppos
ite d
irec
tions
and
rec
ombi
neat
the
rela
y ba
ttery
con
nect
ion.
Now
let u
s tu
rn o
ur a
ttent
ion
to th
e "
dow
n "
stat
ion.
The
line
cur
rent
trav
erse
s th
e U
-ci
rcle
D -
circ
le s
ectio
n of
the
rela
y co
ils, a
nd in
the
dire
ctio
nfr
om U
-ci
rcle
to D
-ci
rcle
.T
here
is n
o co
unte
rbal
anci
ng e
ffec
t fro
m th
e
NO
TE
S O
N T
EL
EG
RA
PHY
.10
1
ethe
r se
ctio
n of
the
coils
, as
ther
e is
no
curr
ent i
n th
e ar
tific
ial c
ircu
it, th
e"
dow
n "
stat
ion'
s ke
y be
ing
at r
est a
nd th
eba
ttery
dis
conn
ecte
d.T
hem
irre
nt is
in th
e co
rrec
t dir
ectio
n to
pro
duce
a m
arki
ng e
ffec
t, an
d th
eha
lal c
ircu
itis
con
sequ
ently
join
ed u
p an
d th
e so
unde
r ac
tuat
ed.
Ade
flec
tion
of th
e ga
lvan
omet
er is
als
o pr
oduc
ed, a
s th
e cu
rren
tpa
sses
thro
ugh
only
one
sec
tion
of th
e ga
lvan
omet
er c
oils
.
Whe
n th
e ke
y at
the
" do
wn
" st
atio
n is
dep
ress
ed th
e ci
rcum
stan
ces
arc
som
ewha
t sim
ilar.
The
cur
rent
fro
m th
e ba
ttery
at t
hat o
ffic
e pa
sses
to th
e ga
lvan
omet
er, w
here
it s
plits
equ
ally
, one
par
t pas
sing
thro
ugh
the
artif
icia
l cir
cuit
and
the
othe
r to
ear
th.
The
cir
cuit
is c
ompl
eted
thro
ugh
the
eart
h co
nnec
tion
at th
e "
up "
sta
tion,
the
U -
circ
le D
-ci
rcle
coi
l of
the
rela
y, a
nd th
ence
thro
ugh
the
back
sto
p of
the
key
and
one
coil
of th
ega
lvan
omet
er to
the
line.
Follo
win
g th
e co
urse
of
the
curr
ent,
it w
ill b
eeb
serv
ed th
at th
e U
-ci
rcle
D -
circ
le c
oil o
f th
e "
dow
n "
stat
ion
rela
y is
trav
erse
d, a
nd th
e ba
ttery
is r
each
ed b
y w
ay o
f th
e re
lay
batte
ry c
on-
nect
ion.
Iii c
ondi
tion
2 bo
th k
eys
are
assu
med
to b
e de
pres
sed,
and
itis
ther
e-fo
re d
esir
ed to
sho
w th
at m
arki
ng e
ffec
ts a
re p
rodu
ced
in b
oth
of th
ere
lays
.A
s in
the
prev
ious
cas
es th
e cu
rren
t fro
m e
ach
of th
e ba
tteri
eshh
euld
be
unde
rsto
od to
pas
s to
the
galv
anom
eter
at t
he r
espe
ctiv
e of
fice
san
d sp
lit. A
cur
rent
is, t
here
fore
, flo
win
g in
eac
h of
the
artif
icia
l cir
cuits
;bu
t wha
t is
the
effe
ct u
pon
the
line
circ
uit?
One
-hal
f of
the
curr
ent f
rom
each
of
the
batte
ries
aff
ects
it, a
nd r
efer
ence
to F
ig. 5
6 w
ill s
how
that
the
batte
ries
pro
duce
cur
rent
s w
hich
flo
w th
roug
h th
e lin
e ci
rcui
t in
the
sam
edi
rect
ion.
The
cur
rent
in th
e lin
e ci
rcui
t is,
ther
efor
e, tw
ice
as g
reat
as
that
in e
ither
of
the
artif
icia
l cir
cuits
, and
the
diff
eren
tially
wou
ndap
para
tus
is c
onse
quen
tly a
ctua
ted
by th
e fo
rmer
or
prep
onde
ratin
g cu
rren
t.A
def
lect
ion
of b
oth
galv
anom
eter
nee
dles
is p
rodu
ced,
and
, as
the
dire
ctio
nof
Hie
line
cur
rent
in th
e re
lays
is f
rom
U -
circ
le to
D -
circ
le, a
mar
king
effe
ct is
reg
iste
red.
The
thir
d co
nditi
on a
ssum
es th
at o
ne k
ey is
bein
g de
pres
sed
and
the
back
con
tact
is b
roke
n, w
hile
the
cont
act a
t the
fro
nt s
top
of th
e ke
yba
il no
t boo
n jo
ined
up.
The
leve
r, in
fac
t, is
in a
n in
term
edia
te p
ositi
on.
The
oth
er k
ey is
ass
umed
to b
e de
pres
sed.
Supp
ose
that
the
" up
"iit
atio
nke
yis
inth
e in
term
edia
te p
ositi
on,
and
the
key
atth
e"
dow
n "
stat
ion
isde
pres
sed.
Inth
ese
cond
ition
sit
isne
cess
ary
to d
emon
stra
te th
at a
spa
cing
eff
ect
is p
rodu
ced
upon
the
" do
wn
"iit
atIo
n's
rela
y, a
ndth
ata
mar
kis
reco
rded
atth
e "
up "
off
ice.
I ad
.it
hofi
rst n
oted
that
, as
ther
e is
no
conn
ectio
n be
twee
n th
e re
lay
and
galv
anom
eter
thro
ugh
the
key
at th
e "
up"
stat
ion,
any
cur
rent
wla
la,la
rea
ches
that
off
ice
from
the
line
mus
t tra
vers
e th
e ar
tific
ial c
ircu
it.T
he te
tal r
esis
tanc
e of
the
path
of
the
curr
ent f
low
ing
thro
ugh
the
line
el m
utt i
s, th
eref
ore,
app
roxi
mat
ely
twic
e as
gre
at a
s be
fore
, and
,up
on
102
NO
TE
S O
N T
EL
EG
RA
PHY
cons
ider
ing
the
curr
ent l
eavi
ng th
e ba
ttery
at t
he d
own
stat
ion,
it w
ill b
ere
adily
see
n th
at it
split
s un
equa
lly, t
he s
tren
gth
of th
e cu
rren
t in
the
artif
icia
l cir
cuit
bein
g tw
ice
as g
reat
as
that
in th
e lin
e.T
he e
ffec
t of
this
pre
pond
erat
ing
curr
ent a
t the
" d
own"
sta
tion
in it
s pa
ssag
e th
roug
hth
e D
-U
coi
l of
the
rela
y is
to c
ause
the
arm
atur
es to
be
held
to th
e sp
acin
gsi
de.
At t
he "
up
" st
atio
n th
e lin
e cu
rren
t onl
y ha
s to
be
cons
ider
ed.
It is
now
abo
ut h
alf
the
stre
ngth
of
the
curr
ents
whi
ch p
asse
d th
roug
hon
e of
the
coils
in c
ondi
tions
1 a
nd 2
;bu
t to
com
pens
ate
for
this
dec
reas
eth
e cu
rren
t now
pas
ses
in th
e sa
me
dire
ctio
n th
roug
h bo
th c
oils
of
the
QS
1111
1111
-
FIG
57.
rela
y an
d al
so th
roug
h bo
th c
oils
of
the
galv
anom
eter
.It
will
, the
refo
re,
be s
een
that
the
mag
netic
eff
ect u
pon
the
rela
y to
ngue
s re
mai
ns u
nalte
red,
and
they
turn
to th
e m
arki
ng s
ide
with
just
as
muc
h fo
rce
as b
efor
e.T
he g
alva
nom
eter
def
lect
ion,
for
a li
ke r
easo
n, r
emai
ns u
ncha
nged
.
The
res
ista
nce
bloc
k r,
whi
ch is
pla
ced
betw
een
the
back
sto
p of
the
key
and
the
rela
y co
nnec
tion,
has
a r
esis
tanc
e ap
prox
imat
ely
equa
l to
that
of th
e ba
ttery
.It
s ob
ject
is to
ens
ure
the
sam
e co
nditi
ons
as r
egar
dsre
sist
ance
whe
n th
e ke
y is
at r
est a
s w
hen
it is
dep
ress
ed.
The
com
plet
e co
nnec
tions
for
the
sing
le c
urre
nt d
uple
x sy
stem
are
show
n in
Fig
. 57. T
HE
DO
UB
LE
CU
RR
EN
T D
UPL
EX
SY
STE
M.
The
dou
ble
curr
ent s
yste
m o
f du
plex
wor
king
is s
imila
r in
man
y re
spec
tsto
that
of
the
sing
le c
urre
nt s
yste
m ;
the
chie
f di
ffer
ence
bei
ng th
at th
e
NO
TE
S O
N T
EL
EG
RA
PHY
.10
3
cond
ition
s ar
e al
tere
d by
the
use
of a
spa
cing
cur
rent
whe
n ei
ther
key
isat
res
t.T
he th
ree
follo
win
g co
nditi
ons
are
impe
rativ
e :-
(1)
With
bot
h ke
ys a
t res
t spa
cing
eff
ects
mus
t be
prod
uced
at b
oth
stat
ions
.
(2)
With
bot
h ke
ys d
epre
ssed
mar
king
eff
ects
mus
t be
prod
uced
at b
oth
stat
ions
.
(3)
With
one
key
dep
ress
ed a
nd th
e ot
her
atre
st, t
he r
elay
mus
tre
spon
d w
ith a
mar
king
eff
ect a
t the
off
ice
whe
re th
e ke
y is
at r
est,
and
with
a s
paci
ng e
ffec
t at t
he o
ther
off
ice.
Fig.
58
show
s th
e th
eore
tical
con
nect
ions
for
dou
ble
curr
ent d
uple
x w
ork-
ing,
bot
h ke
ys b
eing
at r
est.
The
" d
uple
x "
switc
h, b
y w
hich
eith
er d
uple
x
or s
impl
ex w
orki
ng c
an b
e re
sort
ed to
, is
omitt
ed. T
he k
ey s
witc
hes
at b
oth
offi
ces
are
kept
in th
e po
sitio
n to
" s
end
" so
long
as
dupl
exw
orki
ng is
mai
ntai
ned.
Bot
h st
atio
ns b
alan
ce th
e ar
tific
ial c
ircu
it ag
ains
t the
line
and
the
appa
ratu
s in
the
line
circ
uit a
t the
res
pect
ive
dist
ant o
ffic
es.
Aba
lanc
e ha
ving
bee
n ob
tain
ed it
is d
esir
ed to
sho
w th
at th
ene
cess
ary
spac
ing
effe
cts
are
prod
uced
in b
oth
rela
ys.
Con
side
r th
e "
up"
offi
cefi
rst,
and
notic
e th
at th
e cu
rren
t lea
ving
the
posi
tive
pole
of
the
batte
rypa
sses
thro
ugh
the
key
to th
e "
split
" o
f th
e re
lay
whe
re it
div
ides
, one
part
trav
ersi
ng th
e U
-D
coi
l of
the
rela
y, th
e rh
eost
at a
nd o
ne c
oil o
f th
ega
lvan
omet
er.
From
then
ceit
pass
es th
roug
h th
e ke
y to
the
nega
tive
polo
ofth
eba
ttery
.T
he o
ther
half
ofth
e cu
rren
t flo
ws
thro
ugh
104
NO
TE
S O
N T
EL
EG
RA
PHY
.
the
D -
circ
le U
-ci
rcle
coil
of th
e re
lay
to "
ear
th."
Its
path
, whi
ch w
em
ay te
rm th
e lin
e ci
rcui
t, is
con
tinue
d th
roug
h th
e ea
rth
conn
ectio
n at
the
" do
wn
" of
fice
, thr
ough
one
gal
vano
met
er c
oil,
the
key,
D -
circ
leU
-ci
rcle
coi
l of
the
rela
y, a
nd th
ence
to th
e lin
e.It
then
pas
ses
thro
ugh
one
coil
of th
e "
up "
off
ice
galv
anom
eter
and
re
-uni
tes
with
the
curr
ent
flow
ing
in th
e ar
tific
ial c
ircu
it.N
ow c
onsi
der
the
curr
ent e
man
atin
gfr
om th
e "
dow
n "
offi
ce b
atte
ry-t
he c
ircu
mst
ance
s ar
e id
entic
al w
ithth
ose
at th
e "
up "
off
ice,
exc
ept t
hat t
he e
arth
and
line
con
nect
ions
are
reve
rsed
.O
ne h
alf
of th
e cu
rren
t tra
vers
es th
e "
dow
n "
offi
ce a
rtif
icia
lci
rcui
t, an
d th
e ot
her
half
the
line
circ
uit.
It w
ill, t
here
fore
, be
seen
DO
WN
STA
TIO
N
FIG
59.
that
a c
urre
nt f
low
s th
roug
h ea
ch o
f th
e ar
tific
ial c
ircu
its, a
nd th
at e
ach
batte
ry s
ends
a c
urre
nt to
the
line
circ
uit.
The
D -
circ
le U
-ci
rcle
coi
lof
eac
h of
the
rela
ys is
in th
e lin
e ci
rcui
t, an
d th
e ef
fect
s up
on th
eso
unde
rs d
epen
d up
on w
heth
er th
e cu
rren
ts f
low
ing
in th
is c
ircu
it ar
egr
eate
r or
less
than
thos
e fl
owin
g in
the
artif
icia
l cir
cuits
, and
als
o up
onth
e di
rect
ion
of th
e pr
epon
dera
ting
curr
ent.
Whe
n bo
th k
eys
are
at r
est t
he b
atte
ries
act
con
join
tly u
pon
the
line
circ
uit a
nd s
uppl
y cu
rren
ts in
that
cir
cuit
whi
ch f
low
in th
e sa
me
dire
ctio
n.T
he r
esul
tanl
; cur
rent
is, o
bvio
usly
, tw
ice
as s
tron
g as
the
curr
ent i
nei
ther
of
the
artif
icia
l cir
cuits
, con
sequ
ently
the
rela
ys a
re a
ffec
ted
by th
ecu
rren
t flo
win
g in
the
D -
circ
le U
-ci
rcle
coi
ls.
The
dir
ectio
n of
this
curr
ent i
n bo
th c
ases
is f
rom
D -
circ
le to
U -
circ
le, a
nd a
spa
cing
eff
ect i
spr
oduc
ed a
t bot
h of
fice
s.
NO
TE
S O
N T
EL
EG
RA
PHY
.10
5
Con
ditio
n 2
prov
ides
for
bot
h ke
ys b
eing
dep
ress
ed.
Cle
arly
, the
onl
ydi
ffer
ence
fro
m c
ondi
tion
1 is
that
the
batte
ry c
onne
ctio
ns a
t bot
h of
fice
sar
e re
vers
ed, c
onse
quen
tlyth
ere
lays
are
agai
naf
fect
ed b
y th
e pr
e-po
nder
atin
g cu
rren
t flo
win
g in
the
line
circ
uit.
As
the
curr
ents
are
now
reve
rsed
, !na
rkin
g ef
fect
s ar
e pr
oduc
ed a
nd th
e so
unde
rs a
ctua
ted.
In c
ondi
tion
3 on
e ke
y on
ly is
dep
ress
ed, t
he o
ther
bei
ng a
t res
t.Fi
g.hi
), in
whi
ch th
e ke
y at
the
" up
"of
fice
is d
epre
ssed
, illu
stra
tes
this
diag
ram
atic
ally
.T
he c
urre
nt f
rom
eac
h of
the
batte
ries
mus
t be
assu
med
to s
plit
as b
efor
e, th
at e
man
atin
g fr
om th
e "
up "
off
ice
batte
ry d
ivid
ing
thro
ugh
the
galv
anom
eter
coi
ls, a
nd th
at f
rom
the
" do
wn"
off
ice
batte
ryat
the
" sp
lit "
of th
e re
lay.
The
dir
ectio
n of
the
curr
ents
trav
ersi
ngth
e ar
tific
ial c
ircu
its is
indi
cate
d by
arr
ows.
As
rega
rds
the
line
circ
uit,
it w
ill b
e ob
serv
ed th
at th
e cu
rren
t fro
m o
ne o
ffic
e is
opp
osed
by
that
from
the
othe
r, a
nd, a
s a
cons
eque
nce
of th
e eq
ualit
y of
the
oppo
sing
curr
ents
, neu
tral
isat
ion
ensu
es.
The
line
cir
cuit
bein
g de
void
of
curr
ent,
the
effe
cts
upon
the
appa
ratu
s ar
e pr
oduc
ed b
y th
e cu
rren
ts tr
aver
sing
the
artif
icia
l cir
cuits
.A
t the
" u
p "
offi
ce th
e cu
rren
t pas
ses
thro
ugh
the
1)-U
coi
l of
the
rela
y in
a d
irec
tion
whi
ch r
esul
ts in
a s
paci
ng e
ffec
t, w
hile
itt th
e "
dow
n" o
ffic
e a
mar
king
eff
ect i
s pr
oduc
ed b
y th
e pa
ssag
e of
the
curr
ent t
hrou
gh th
e co
rres
pond
ing
rela
y co
il, b
ut in
the
oppo
site
dir
ectio
n.
Acl
oser
exa
min
atio
nof
the
artif
icia
lci
rcui
t may
now
be
mad
e.I
ither
to, i
n de
alin
g w
ith th
e du
plex
sys
tem
s, th
e lin
e ha
s be
en c
on-
side
red
as p
osse
ssin
g th
e pr
oper
ty o
f re
sist
ance
onl
y, th
e el
ectr
o-st
atic
capa
city
of
the
line
not h
avin
g be
en to
uche
d up
on in
ord
er to
sim
plif
yth
e ex
plan
atio
n of
the
theo
ry o
f th
e sy
stem
s.T
he "
cap
acity
," h
owev
er,
is a
fac
tor
not t
o be
ove
rloo
ked.
The
infl
uenc
e of
the
stat
ic c
ondi
tions
of a
long
cir
cuit,
in p
rodu
cing
ret
ardi
ng a
nd p
rolo
ngin
g ef
fect
s up
onth
e cu
rren
t, is
suc
h th
at, u
nles
s th
e el
ectr
o-st
atic
cap
acity
of
the
line
isre
prod
uced
in th
e ar
tific
ial c
ircu
it, im
perf
ect s
igna
ls a
re b
ound
to r
esul
t.T
hear
tific
ial
circ
uit
mus
tre
sem
ble
the
lino
circ
uit
ascl
osel
yas
pos
sibl
e.It
sho
uld
be m
ade,
in f
act,
an e
xact
ele
ctri
cal c
ount
er-
part
of
the
line
circ
uit.
The
sta
tic c
ondi
tions
are
pro
duce
d in
the
artif
icia
l cir
cuit
by m
eans
of
a" c
onde
nser
."T
his
piec
e of
app
arat
us in
its s
impl
est f
orm
con
sist
s of
two
cond
ucto
rs s
epar
ated
by
an in
sula
tor.
Tak
e tw
o br
ass
plat
es, A
and
B, w
hich
are
sep
arat
ed b
y a
shee
t of
glas
s,IL
K in
dica
ted
in F
ig. 6
0.W
hen
a ch
arge
of
elec
tric
ity is
giv
en to
eith
erof
thor
n, th
e ch
arge
act
s in
duct
ivel
y up
on th
e ot
her.
A c
harg
e of
elec
tric
ity o
f an
opp
osite
kin
d is
indu
ced
upon
the
near
sid
e of
the
latte
r,an
d an
indu
ced
char
ge s
imila
r in
kin
d to
the
indu
cing
cha
rge
is r
epel
led
to th
e fa
r si
de.
Let
the
plat
e A
be
give
n a
posi
tive
char
ge.
The
indu
ctiv
eac
tion
is to
pro
duce
a n
egat
ive
char
ge u
pon
the
side
of
B n
ear
the
glas
s, a
ndto
rep
el a
pos
itive
cha
rge
to th
e fa
r si
de o
f th
at p
late
. The
neg
ativ
e ch
arge
Id h
eld
boun
d by
the
attr
actin
g in
flue
nce
of th
e ch
arge
upo
n A
, and
the
103
NO
TE
S O
N T
EL
EG
RA
PHY
.
plat
e B
may
be
said
to h
ave
an in
duce
d po
sitiv
e po
tent
ial b
y vi
rtue
of
itsfr
ee p
ositi
ve c
harg
e.It
may
not
be
inap
prop
riat
e to
rei
tera
te h
ere
that
elec
tric
pot
entia
l is
the
term
app
lied
to th
e pr
oper
ty p
osse
ssed
by
a ch
arge
dbo
dy w
hich
det
erm
ines
its
prep
ared
ness
todo
wor
k by
ove
rcom
ing
resi
stan
ce.
If n
ow th
epl
ate
B b
eea
rth
-con
nect
ed th
ere
will
bea
mom
enta
ry d
isch
arge
of
posi
tive
elec
tric
ity, i
n th
e fo
rm o
f a
curr
ent,
from
the
plat
e to
the
eart
h.A
s th
e ea
rth
isat
zer
o po
tent
ial t
hecu
rren
t will
flo
w f
rom
the
poin
t of
the
high
er p
oten
tial,
i.e.,
the
plat
e, to
the
eart
h.T
he r
emai
ning
cha
rge,
whi
ch is
hel
d bo
und,
rea
cts
upon
the
plat
e A
, acc
umul
atin
g its
cha
rge
upon
the
side
nea
r to
the
glas
s an
dm
akin
g it
poss
ible
for
A to
rec
eive
a f
urth
er p
ositi
ve c
harg
e. T
he la
tter,
intu
rn, i
nduc
es a
gre
ater
neg
ativ
e ch
arge
upo
n B
, and
ther
e is
an
acco
m-
pany
ing
disc
harg
e of
pos
itive
ele
ctri
city
to e
arth
.T
he a
ccum
ulat
ion
of
A 4
FIG
-0.
FIG
: 61.
the
char
ge u
pon
A m
ay b
e co
ntin
ued
until
a p
oint
is r
each
ed a
tw
hich
A is
una
ble
to h
old
a fu
rthe
r ch
arge
.It
s ca
paci
ty is
then
sai
d to
be s
atis
fied
.W
ith a
dis
char
ge o
f th
e el
ectr
icity
fro
m th
e pl
ate
A th
ech
arge
upo
n th
e pl
ate
B is
rel
ease
d an
d th
ere
is a
mom
enta
ry r
ush
ofne
gativ
e el
ectr
icity
to e
arth
, or
perh
aps
it w
ould
be
bette
r to
say
the
nega
tive
char
ge u
pon
B is
neu
tral
ised
by
a m
omen
tary
tran
sfer
ence
of
elec
tric
ity in
the
form
of
a cu
rren
t fro
m th
e ea
rth
to th
e pl
ate.
Such
api
ece
of a
ppar
atus
is a
sim
ple
cond
ense
r, a
nd it
s ac
tion
is a
nalo
gous
toth
at w
hich
take
s pl
ace
in a
tele
grap
h ci
rcui
t.W
hen
a ba
ttery
is jo
ined
to a
tele
grap
h lin
e th
e la
tter
beco
mes
cha
rged
with
sta
tic e
lect
rici
ty, a
ndth
e re
actio
ns w
hich
take
pla
ce b
etw
een
the
line
and
the
eart
h an
d co
n-du
ctor
s in
its
vici
nity
are
sim
ilar
to th
e ef
fect
s of
indu
ctio
n be
twee
n th
etw
o pl
ates
of
the
cond
ense
r.T
he li
ne, i
n fa
ct, b
ecom
es o
ne p
late
of
aco
nden
ser,
the
othe
r pl
ate
bein
g th
e ea
rth
and
neig
hbou
ring
con
duct
ors.
Unt
il th
e lin
e ha
s be
en c
harg
ed to
its
fulle
st c
apac
ity th
e cu
rren
t doe
sno
t pas
s to
the
dist
ant s
tatio
n, a
nd th
e ef
fect
of
reta
rdat
ion
is p
rodu
ced.
NO
TE
S O
N T
EL
EG
RA
PHY
.10
7
AH
soo
n as
the
batte
ry is
cut
off
the
char
ge a
ccum
ulat
ed u
pon
the
wir
epa
sses
to e
arth
, thu
s pr
olon
ging
the
curr
ent.
The
fun
ctio
n th
en o
f th
eco
nden
ser
in th
e ar
tific
ial c
ircu
it of
a d
uple
x se
t is
to r
epro
duce
the
stat
icef
fect
s of
the
line.
The
pra
ctic
al f
orm
of
cond
ense
r, to
mee
t the
req
uire
men
ts o
f a
tele
grap
hci
rcui
t, di
ffer
s fr
om th
at f
irst
des
crib
ed, b
ut th
e th
eory
of
its a
ctio
n is
the
sam
e.A
ll co
nden
sers
are
com
pose
des
sent
ially
oftw
o co
nduc
tors
sepa
rate
d by
an
insu
lato
r, th
e la
tter
bein
g kn
own
as th
e di
-el
ectr
ic.
The
cap
acity
of
a co
nden
ser
depe
nds
upon
the
thre
e fo
llow
ing
con-
ditio
ns, v
iz. :
-1.
The
siz
e of
the
plat
es ;
2. T
he d
ista
nce
betw
een
the
plat
es ;
3. T
he s
peci
fic
indu
ctiv
e ca
paci
ty o
f th
e in
sula
ting
med
ium
or
di -
elec
tric
.
For
a la
rge
capa
city
the
plat
es o
ppos
ed to
eac
h ot
her
mus
tpo
sses
sa
cons
ider
able
sur
face
are
a.T
he la
rger
the
plat
es in
this
res
pect
the
grea
ter
will
be
the
indu
ctio
n be
twee
n th
em, a
nd th
e ca
paci
ty w
ill a
ccor
d-in
gly
incr
ease
in d
irec
t pro
port
ion
to th
e su
rfac
e ar
ea o
f th
e pl
ates
.In
stan
dard
con
dens
ers
mic
a is
em
ploy
ed a
s th
e in
duct
ive
med
ium
, but
its
com
para
tivel
y gr
eat
cost
pre
clud
es th
e ge
nera
l use
of
this
mat
eria
l.Pa
raff
ined
pap
er a
s a
di -
elec
tric
, how
ever
, is
foun
d to
sui
t adm
irab
ly f
oral
l pra
ctic
al p
urpo
ses,
and
by
its u
se in
con
junc
tion
with
she
ets
of ti
n fo
ilas
the
plat
es th
e co
st o
f m
akin
g a
cond
ense
r is
con
side
rabl
y re
duce
d.A
larg
e nu
mbe
r of
she
ets
of ti
n fo
il is
em
ploy
ed, a
nd th
e al
tern
ate
shee
ts a
reso
con
nect
ed th
at th
ey f
orm
two
very
larg
e co
nduc
ting
surf
aces
, whi
ch a
rese
para
ted
by a
di -
elec
tric
of
com
para
tivel
y hi
gh s
peci
fic
indu
ctiv
e ca
paci
ty.
Ow
ing
to b
oth
para
ffin
ed p
aper
and
tin
foil
bein
g m
anuf
actu
red
in v
ery
thin
she
ets
it is
pos
sibl
e to
com
pres
s th
em in
to a
sm
all c
ompa
ss, a
nd c
on-
sequ
ently
the
plat
es a
re b
ioug
ht q
uite
clo
se to
geth
er.
By
this
mea
nsco
nditi
on 2
is f
ulfi
lled,
and
the
indu
ctiv
e ef
fect
bet
wee
n th
e pl
ates
isob
viou
sly
incr
ease
d.
The
spe
cifi
c in
duct
ive
capa
city
of
a di
-el
ectr
ic is
the
pecu
liar
prop
erty
poss
esse
d by
all
insu
latin
g m
ater
ials
, in
vary
ing
degr
ees,
of
allo
win
gin
duct
ion
to ta
ke p
lace
acr
oss
them
.T
akin
g th
esp
ecif
icin
duct
ive
capa
city
of
air
as u
nity
, the
app
roxi
mat
e re
lativ
e va
lues
of
othe
r di
-ele
ctri
csar
e :-
Gla
ss1.
9Pa
raff
in1.
9In
dia
-rub
ber
2.8
Gut
ta-p
erch
a4.
2M
ica
5
It w
ill, t
here
fore
, be
seen
that
mic
a is
the
best
sub
stan
ce to
use
in th
eco
nstr
uctio
nof
aco
nden
ser.
Ass
umin
gal
lot
her
cond
ition
sto
108
NO
TE
S O
N T
EL
EG
RA
PHY
.
beeq
ual,
the
capa
city
ofan
air
cond
ense
ris
only
one
-fif
thth
atof
aco
nden
ser
inw
hich
the
di -
elec
tric
ism
ica.
The
hig
h sp
ecif
ic in
duct
ive
capa
city
of
the
latte
r re
nder
s it
inva
luab
lew
hen
a co
nden
ser
of g
reat
eff
icie
ncy
and
relia
bilit
y is
req
uire
d.M
ica,
too,
may
be
cut i
nto
very
thin
laye
rs, a
nd th
is is
als
o an
adv
anta
ge o
ver
man
yot
her
insu
latin
g m
ater
ials
. For
var
ious
rea
sons
the
othe
r di
-ele
ctri
cs e
nu-
mer
ated
abo
ve a
re n
ot s
uita
ble,
and
the
best
sub
stitu
te f
or m
ica
is f
ound
in p
araf
fine
d pa
per,
whi
ch is
an
effi
cien
t ins
ulat
or a
nd p
osse
sses
a c
om-
para
tivel
y hi
gh s
peci
fic
indu
ctiv
e ca
paci
ty.
Con
dens
ers
inte
nded
for
use
upon
tele
grap
hci
rcui
ts a
re m
ade
inse
ctio
ns, a
nd b
y m
eans
of
bras
s bl
ocks
and
plu
gs th
ey m
ay b
e re
adily
adju
sted
to th
e va
ryin
g co
nditi
ons
of th
e lin
e.T
he a
ltern
ate
shee
ts o
f
0
FIG
Q9.
.
tin f
oil a
re c
onne
cted
toge
ther
and
join
ed to
one
term
inal
of
the
inst
ru-
men
t.T
he r
emai
nder
are
div
ided
into
sec
tions
, eac
h of
whi
ch is
con
-ne
cted
to a
n in
sula
ted
bras
s bl
o?,k
.C
onne
ctio
n be
twee
n th
ese
bloc
ks a
nda
bras
s st
rip,
upo
n w
hich
is f
itted
the
seco
nd te
rmin
al o
f th
e co
nden
ser,
is m
ade
by m
eans
of
coni
cal b
rass
plu
gs.
To
obta
in th
e m
axim
umca
paci
ty th
e w
hole
of
the
plug
s m
ust b
e in
sert
ed (
an o
ppos
ite o
pera
tion
toth
at r
equi
red
for
brin
ging
res
ista
nce
into
a c
ircu
it).
The
cap
acity
of
the
cond
ense
r ge
nera
lly u
sed
upon
land
line
s fo
r ba
lanc
ing
dupl
ex c
ircu
its is
7.25
mic
ro -
fara
ds, a
nd b
y th
e m
anip
ulat
ion
of th
e pl
ugs
any
valu
e w
ithin
that
lim
it, b
y gr
adat
ions
of
a qu
arte
r of
a m
icro
-fa
rad,
may
be
obta
ined
.T
he a
rran
gem
ent i
s sh
own
in F
ig. 6
2.
NO
TE
S O
N T
EL
EG
RA
PHY
.10
9
The
act
of
char
ging
and
dis
char
ging
a lo
ng li
ne is
not
eff
ecte
d in
stan
-ta
neou
sly,
and
the
char
ging
and
dis
char
ging
of
the
cond
ense
r m
ust,
ther
efor
e,be
del
ayed
or
slow
ed d
own
in o
rder
that
the
stat
ic c
ondi
tions
in th
e ar
tific
ial
circ
uit m
ay r
esem
ble
thos
e in
the
line.
Thi
s re
tard
ing
effe
ct is
bro
ught
abo
utby
incl
udin
g re
sist
ance
coi
ls in
the
path
of
the
char
ge.
The
bra
ss s
trip
isus
ually
div
ided
into
two
port
ions
, so
that
bet
wee
n th
em m
ay b
e pl
aced
an
adju
stab
le s
et o
f re
sist
ance
coi
ls, c
alle
d th
e "
cond
ense
r "
coils
.In
a c
on-
dens
er th
us d
ivid
ed o
ne p
ortio
n re
pres
ents
the
capa
city
of
the
near
end
and
the
othe
r th
e fa
r en
d of
the
line.
The
pro
cess
of
char
ging
and
dis
char
ging
the
cond
ense
r is
als
o re
gula
ted
by a
noth
er s
et o
f re
sist
ance
coi
ls, t
hrou
ghw
hich
the
char
ge p
asse
s.T
hese
coi
ls a
re te
rmed
" r
etar
datio
n co
ils."
As
the
capa
city
of
long
cab
le c
ircu
its is
con
side
rabl
e it
is u
sual
ly n
eces
sary
toco
nstr
uct t
he c
onde
nser
in th
ree
port
ions
, bet
wee
n ea
ch o
f w
hich
a s
et o
fre
sist
ance
coi
ls is
inse
rted
, and
this
is te
rmed
a "
trip
le "
con
dens
er.
FIC
G3.
The
cap
acity
of
the
artif
icia
l cir
cuit
may
be
adju
sted
by
notic
ing
the
effe
ct u
pon
the
diff
eren
tial g
alva
nom
eter
whe
n ch
argi
ng a
nd d
isch
argi
ngth
eco
nden
ser.
With
ape
rfec
t bal
ance
the
galv
anom
eter
will
not
be a
ffec
ted,
as
the
disc
harg
es f
rom
the
line
and
cond
ense
r w
ill n
eutr
alis
eea
ch o
ther
, but
if th
e ca
paci
ty o
f th
e on
e is
gre
ater
than
that
of
the
othe
r,a
slig
ht m
omen
tary
def
lect
ion
will
be
obse
rved
whe
n th
e ke
y is
dep
ress
edor
rai
sed.
If th
e ca
paci
ty in
sert
ed in
the
cond
ense
r is
not
suf
fici
ent t
oef
fect
a b
alan
ce, t
he d
efle
ctio
n of
the
galv
anom
eter
nee
dle
will
be
in a
nup
war
d di
rect
ion
whe
n th
e ke
y is
dep
ress
ed, a
nd d
ownw
ard
whe
n th
e ke
yis
rel
ease
d.If
the
defl
ectio
ns a
re in
the
oppo
site
dir
ectio
ns th
e ef
fect
ive
cond
ense
r ca
paci
ty is
too
grea
t.A
def
lect
ion
in th
e sa
me
dire
ctio
nw
hen
the
key
is r
elea
sed
as w
hen
itis
dep
ress
edin
dica
tes
that
the
reta
rdat
ion
coils
req
uire
re
-adj
ustm
ent.
As
the
galv
anom
eter
, how
ever
,
110
NO
TE
S O
N T
EL
EG
RA
PHY
.
is n
ot s
uffi
cien
tly s
ensi
tive
to o
btai
n a
fine
adj
ustm
ent i
t is
a m
uch
bette
rpl
an to
adj
ust t
he c
onde
nser
to th
e pa
ssag
e of
wor
king
sig
nals
. The
eff
ect
of a
n im
perf
ect e
lect
ro-s
tatic
bal
ance
is to
pro
duce
fal
se d
ots
upon
the
.Dow
n L
ine
or-
Eei
ne4,
1111
1111
FIG
. CA
Up
Lun
eor
C A
rt4
rece
ivin
g ap
para
tus
at th
e se
ndin
g st
atio
n, a
nd th
ere
dist
ort t
he s
igna
lsw
hich
are
bei
ng r
ecei
ved.
A g
ood
plan
whi
ch m
ay b
e ad
opte
d to
pro
duce
a fi
ne a
djus
tmen
t is
to f
irst
obt
ain
an a
ppro
xim
ate
bala
nce,
and
then
fin
d
NO
TE
S O
N T
EL
EG
RA
PHY
.11
1
out b
y ex
peri
men
t the
max
imum
and
min
imum
cap
aciti
es, i
n ea
ch d
ivis
ion
of th
e co
nden
ser,
at w
hich
fal
se s
igna
ls a
ppea
r.T
he m
ean
betw
een
the
two
ghou
ld b
e th
e re
quir
ed c
apac
ity f
or th
at s
ectio
n.T
he r
esis
tanc
e in
the
cond
ense
r co
ils a
nd r
etar
datio
n co
ils s
houl
d be
sim
ilarl
y de
alt w
ithse
para
tely
, and
the
mea
n of
the
valu
es a
t whi
ch th
e fa
lse
sign
als
are
prod
uced
in e
ach
case
sho
uld
be a
dopt
ed f
or w
orki
ng p
urpo
ses.
The
theo
retic
al c
onne
ctio
ns o
f th
e ar
tific
ial c
ircu
it ar
e in
dica
ted
in F
ig. 6
3,R
1 re
pres
entin
g th
e re
tard
atio
n co
ils, a
nd R
2 th
e co
nden
ser
coils
, whi
lea
com
plet
e di
agra
m o
f th
e ap
para
tus
and
conn
ectio
ns r
equi
red
for
doub
lecu
rren
t dup
lex
wor
king
is s
how
n in
Fig
. 64.
The
re a
re tw
o m
etho
ds o
f co
nnec
ting
cond
ense
rs.
Figs
. 65
and
66 s
how
how
thre
e co
nden
sers
may
be
join
ed.
The
for
mer
illu
stra
tes
the
ordi
nary
TT
ri()
Gs.
FIG
66
met
hod
of a
ugm
entin
g th
e ca
paci
ty b
y in
crea
sing
the
size
of
the
oppo
sing
plat
es, t
he e
ffec
tive
capa
city
of th
e th
ree
cond
ense
rs 0
1, 0
2, a
nd 0
3 jo
ined
in th
is m
anne
r be
ing
the
sum
of
thei
r se
para
te c
apac
ities
.
Fig.
66
indi
cate
s th
e"
casc
ade
" ar
rang
emen
t, by
mea
ns o
f w
hich
aca
paci
ty le
ss th
an th
e sm
alle
stof
the
thre
e is
obt
aine
d.B
y th
is m
etho
don
e pl
ate
of th
e co
nden
ser
(), i
s op
pose
dto
one
of
the
plat
es o
f 08
by
way
of 0
2.T
he d
ista
nce
betw
een
thes
e pl
ates
, for
pur
pose
s of
indu
ctio
n, is
thre
e tim
esas
gre
at a
s th
at b
etw
een
the
plat
esof
eith
er o
ne o
f th
e co
nden
sers
, and
, as
the
capa
city
is in
vers
ely
prop
ortio
nal t
o th
e di
stan
ce b
etw
een
the
plat
es,
the
capa
city
in th
is in
stan
ce w
ill b
e on
ly o
ne-t
hird
that
of
one
of th
e co
n-de
nser
s, a
ssum
ing
that
they
eac
h ha
veth
e sa
me
capa
city
.T
he a
nalo
gybe
twee
n th
is s
yste
m a
nd th
e co
nnec
tion
of r
esis
tanc
es in
" p
aral
lel a
rc "
will
be
appa
rent
, and
the
sam
e la
w a
pplie
s.T
he c
apac
ity o
f th
roe
cond
ense
rs jo
ined
in c
asca
de is
1
96N
OT
ES
ON
TE
LE
GR
APH
Y.
CH
APT
ER
XIV
.
TH
E D
IFFE
RE
NT
IAL
DU
PLE
X S
YST
EM
.
To
incr
ease
the
amou
nt o
f tr
affi
c th
at m
ay b
e de
alt w
ith u
pon
a si
ngle
wir
e ci
rcui
t, m
eans
hav
e be
en a
dopt
ed w
here
by s
igna
ls c
an b
e se
nt a
ndre
ceiv
ed s
imul
tane
ousl
y at
bot
h en
ds o
f th
e lin
e.T
his
syst
em o
f w
orki
ngis
kno
wn
as th
e "
Dup
lex"
sys
tem
, and
the
" ca
rryi
ng c
apac
ity "
of
the
circ
uit i
s ap
prox
imat
ely
twic
e as
gre
at a
s th
at o
f a
" si
mpl
ex "
cir
cuit.
Exp
erie
nce,
how
ever
, has
sho
wn
that
two
circ
uits
of
the
latte
r cl
ass
will
give
bet
ter
wor
king
res
ults
than
one
" d
uple
x "
circ
uit,
and
dupl
ex w
ork-
ing
shou
ld o
nly
be r
esor
ted
to w
hen
itis
fou
nd th
at a
ll th
e av
aila
ble
FIG
.51
" si
mpl
ex "
cir
cuits
are
insu
ffic
ient
to c
arry
the
traf
fic.
The
pri
ncip
le o
fth
e "
diff
eren
tial "
sys
tem
of
dupl
ex w
orki
ng is
bas
ed u
pon
the
fact
that
whe
n a
curr
ent s
plits
thro
ugh
two
,,Ath
s of
equ
al r
esis
tanc
es, t
hecu
rren
ts w
hich
flo
w th
roug
h th
em a
re e
qual
. In
the
syst
em u
nder
con
side
ra-
tion
the
rela
y an
d ga
lvan
omet
er a
re d
iffe
rent
ially
wou
nd, s
o th
at w
hen
curr
ents
of
equa
l str
engt
h pa
ss th
roug
h th
e tw
o se
ctio
ns o
f th
e co
ils o
fei
ther
inst
rum
ent i
nop
posi
te d
irec
tions
,th
e ef
fect
of o
ne s
ectio
n is
neut
ralis
ed b
y th
at o
f th
e ot
her.
Whe
n, h
owev
er, t
he c
urre
nt in
one
sect
ion
isgr
eate
r th
an th
at in
the
othe
r, th
e in
stru
men
t is
affe
cted
by
virt
ue o
f th
e pr
epon
dera
ting
curr
ent a
nd w
ill r
espo
nd a
ccor
ding
to th
edi
rect
ion
in w
hich
that
cur
rent
pas
ses.
In th
e du
plex
sys
tem
an
artif
icia
l cir
cuit
is m
ade
up a
nd b
alan
ced
agai
nst t
he li
ne c
ircu
it by
mea
ns o
f re
sist
ance
coi
ls a
nd, w
here
nec
essa
ry,
iszo
'rEs
ON
TE
LE
GR
APH
Y.
c)7
cond
ense
rs.
The
obj
ect o
f th
e ar
tific
ial
circ
uit i
s to
pro
duce
an
exac
tel
ecir
ical
coa
.iier
part
of
the
line,
so
that
whe
n a
curr
ent s
plits
thro
ugh
the
circ
uits
the
curr
ents
whi
ch r
esul
t sha
ll be
equ
al in
str
engt
h an
dsi
mila
rly
affe
cted
by
the
stat
ic c
ondi
tions
pre
vaili
ng.
Bef
ore
atte
mpt
ing
to d
escr
ibe
the
actu
al w
orki
ng o
f th
e du
plex
sys
tem
It w
ill b
e w
ell,
perh
aps,
to c
onsi
der
how
the
rela
y is
aff
ecte
d by
the
curr
ents
pas
sing
thro
ugh
it. T
he r
elay
sho
uld
bo lo
oked
upo
n as
the
rece
ivin
gin
stru
men
t, as
the
soun
der
is o
nly
actu
ated
whe
n th
e cu
rren
ts w
hich
pas
sth
roug
h th
e co
ils o
f th
e re
lay
are
such
as
to c
lose
the
loca
l cir
cuit.
For
dupl
ex w
orki
ng th
e co
ils o
f th
e re
lay
are
inva
riab
ly jo
ined
up
in "
ser
ies,
"an
d w
hen
a cu
rren
tpa
sses
thro
ugh
them
fro
m "
left
" to
" ri
ght,"
as
show
n in
Fig
. 51,
the
effe
ctup
on th
e ar
mat
ures
is to
cau
se th
e la
tter
to tu
rnto
war
ds th
e le
ft.
A c
urre
nt in
the
reve
rse
dire
ctio
n pr
oduc
es a
n op
posi
teor
mar
king
eff
ect,
and
join
s up
the
loca
l bat
tery
cir
cuit,
and
the
soun
der
Fra5
-3.
FIG
. 54.
isac
tuat
ed.
It s
houl
d be
rem
embe
red
that
the
curr
ent c
ause
s th
ear
mat
ures
to tu
rn in
the
oppo
site
dir
ectio
n to
that
in w
hich
it is
flo
win
g.Pi
g. 5
2 sh
ows
the
curr
ent c
omin
g in
at t
he "
spl
it "
of th
e re
lay,
and
, if
the
resi
stan
ces
upon
eith
ersi
deof
the
rela
yar
eeq
ual,
itw
ill d
ivid
eeq
ually
,thr
ough
the
two
path
s.T
hetw
ocu
rren
tsth
uspr
o-du
ced
will
pass
thro
ugh
the
coils
inop
posi
tedi
rect
ions
, and
the
effe
ct o
f th
e on
e w
ill n
eutr
alis
e th
at o
f th
e ot
her.
The
arm
atur
es w
illco
nseq
uent
ly r
emai
n un
dist
urbe
d.Sh
ould
one
ofth
ecu
rren
ts b
eag
men
ted
inst
reng
th b
y co
mbi
natio
n w
ith a
noth
er th
e re
lay
will
be a
ctua
ted
by th
e in
crea
sed
curr
ent.
Whe
n th
ecu
rren
t in
eith
erse
ctio
n of
the
rela
y is
neu
tral
ised
by
the
oppo
sitio
n of
ano
ther
cur
rent
of
ori t
tal s
tren
gth,
the
effe
ct u
pon
the
rela
y w
ill b
e pr
oduc
ed b
y th
e cu
rren
t in
time
othe
r se
ctio
n of
the
rela
y co
ils, a
nd w
ill b
e "
mar
king
" o
r "
spac
ing
"ac
cord
ing
to th
e di
rect
ion
in w
hich
that
cur
rent
is f
low
ing.
The
eff
ect o
f a
114
NO
TE
S O
N T
EL
EG
RA
PHY
.
The
ele
ctro
de in
con
nect
ion
with
the
posi
tive
pole
of
the
prim
ary
batte
ry is
term
ed th
e "
anod
e,"
and
its p
ole
is th
epo
sitiv
e po
leof
/the
seco
ndar
y ce
ll.T
he e
lect
rode
in c
onne
ctio
n w
ith th
ene
gativ
e po
ofth
e pr
imar
y ba
ttery
is te
rmed
the
" ka
thod
e,"
and
itspo
le is
the
nega
tive
polo
of
the
seco
ndar
y ce
ll.T
he r
easo
n fo
r th
us n
amin
g th
e po
les
isap
pare
nt u
pon
cons
ider
atio
n of
the
fact
that
the
hydr
ogen
at t
he k
atho
deis
ele
ctro
-pos
itive
to th
eox
ygen
at t
he a
node
, and
that
the
form
er a
cts
as th
e po
sitiv
e an
d th
e la
tter
as th
e ne
gativ
e pl
ate
of a
nor
dina
ry c
ell.
The
re is
a d
iffe
renc
e of
pot
entia
l of
1.47
vol
t bet
wee
nhy
drog
en a
ndox
ygen
, the
refo
rea
grea
ter
elec
tro-
mot
ive
forc
e th
an th
is m
ust b
eem
ploy
ed to
dec
ompo
se w
ater
.It
will
be
seen
fro
m th
e ab
ove
rem
arks
that
the
seco
ndar
y cu
rren
t is
due
to c
hem
ical
re
-act
ions
, con
sequ
ently
the
term
"se
cond
ary
" is
mor
e ap
pli-
cabl
e to
a c
ell o
f th
is k
ind
than
the
mor
ege
nera
l ter
m o
f "
accu
mul
ator
."T
o am
plif
y th
is,
cons
ider
an
exha
uste
d "
Dan
iell
"ba
ttery
.W
hen
aco
mpa
rativ
ely
stro
ng c
urre
nt is
pas
sed
thro
ugh
it in
the
dire
ctio
n fr
omco
pper
to z
inc,
i.e.
, in
the
reve
rse
dire
ctio
n to
that
of
the
prop
er c
urre
nt,
chem
ical
re
-act
ions
take
pla
ce, a
nd th
e ba
ttery
isag
ain
capa
ble
of b
eing
used
-in
the
prim
ary
sens
e-as
a s
ourc
e of
ele
ctri
cal e
nerg
y.T
he s
impl
e ga
s ba
ttery
is o
f lit
tle p
ract
ical
use
;bu
t Pla
nte,
in th
eye
ar18
60, i
ntro
duce
d le
ad s
heet
s as
the
elec
trod
es, a
nd a
sol
utio
n of
sulp
huri
cac
id (
H2
SO4)
as
the
elec
trol
yte.
Upo
n pa
ssin
ga
curr
ent t
hrou
gh th
e el
ectr
o-ly
te o
xyge
n w
as f
ound
to c
ombi
ne w
ith th
e an
ode-
the
plat
e at
whi
ch th
ecu
rren
t ent
ers
the
cell-
and
form
, with
the
lead
,pe
roxi
de o
f le
ad (
Pb02
)w
hile
the
evol
ved
hydr
ogen
was
libe
rate
d at
the
kath
ode.
Pero
xide
of
lead
is a
n in
solu
ble
com
poun
d, a
nd w
hen
oppo
sed
to a
cle
an s
urfa
ceof
lead
, the
kat
hode
, a d
iffe
renc
e of
pot
entia
l of
abou
t 2 to
2.5
volts
is o
btai
ned.
Plan
te u
sed
larg
e sh
eets
of
lead
rol
led
up s
pira
lly, b
ut n
otin
con
tact
, and
imm
erse
d th
em in
dilu
te s
ulph
uric
aci
d.B
y re
peat
edly
char
ging
, dis
char
ging
or
rech
argi
ng th
e ce
ll in
rev
erse
dir
ectio
ns th
eam
ount
of
activ
e m
ater
ial w
as c
onsi
dera
bly
incr
ease
dby
mak
ing
the
surf
aces
of
the
lead
pla
tes
poro
us b
y ch
emic
al a
ctio
n.W
hen
the
seco
ndar
y cu
rren
t was
pro
duce
d th
e hy
drog
en a
dher
ing
to th
e ka
thod
eco
mbi
ned
with
som
e of
the
oxyg
en o
f th
e pe
roxi
de o
f le
ad a
t the
anod
ean
d fo
rmed
wat
er, w
hile
the
surf
ace
of th
e ka
thod
ew
as a
lso
oxid
ised
by
the
rele
ase
of o
xyge
n fr
om th
e el
ectr
olyt
e.T
he p
erox
ide
of le
ad a
t the
anod
e w
as d
epri
ved
of s
ome
of it
s ox
ygen
, and
the
surf
ace
of th
ean
ode
was
left
in a
por
ous
or s
pong
y st
ate.
Whe
n th
e se
cond
ary
cell
had
prac
tical
ly e
xhau
sted
itse
lf th
epr
imar
ycu
rren
t was
aga
in a
pplie
d, a
nd th
e ox
idis
ed1;
.7a
at th
e ka
thod
e w
asre
duce
d to
spo
ngy
lead
, whi
le th
e en
larg
ed s
urfa
ce o
f th
e an
ode
agai
nbe
cam
e co
vere
d w
ith p
erox
ide
of le
ad.
The
se a
ctio
ns o
f ch
argi
ng a
nddi
scha
rgin
g, w
hich
res
ulte
d in
the
enla
rgem
ent o
f th
e su
rfac
es o
f th
e
NO
TE
S O
N T
EL
EG
RA
PHY
.11
5
plat
es, a
fter
hav
ing
been
in o
pera
tion
for
som
e tim
e w
ere
disc
ontin
ued,
and
the
" fo
rmat
ion
" of
the
plat
es p
roce
eded
by
loca
l act
ion,
the
sulp
hien
of th
e su
lphu
ric
acid
com
bini
ng w
ith th
e le
ad.
Alth
ough
the
pero
xide
still
rem
aine
d up
on o
ne o
f th
e pl
ates
, the
loca
l act
ion
took
pla
ce b
etw
een
its p
artic
les,
with
the
resu
lt th
at b
oth
plat
es e
vent
ually
bec
ame
coat
ed w
ithsu
lpha
te o
f le
ad.
Thi
s m
etho
d of
" fo
rmin
g,"
how
ever
, ent
aile
d co
nsid
erab
le la
bour
,ex
pens
e an
d lo
ss o
f tim
e. I
t was
als
o lim
ited
by th
e m
echa
nica
lw
eake
ning
of th
e pl
ates
by
incr
easi
ng th
eir
poro
sity
.
In th
e ye
ar 1
880
a co
nsid
erab
le im
prov
emen
t was
eff
ecte
d by
Fau
re,
who
mad
e a
past
e of
lead
sul
phat
e (P
bSO
4) b
y m
ixin
g su
lphu
ric
acid
(1:1
2SO
4) a
nd r
ed le
ad, o
r m
iniu
m (
Pb30
4), a
nd a
pply
ing
it to
both
plat
es.
The
am
ount
of
elec
tric
al e
nerg
y ne
cess
ary
to p
rodu
ce s
pong
y le
ad w
asby
this
mea
ns c
onsi
dera
bly
redu
ced.
The
pas
te a
t the
pos
itive
pla
te, o
ran
ode,
was
con
vert
ed in
to p
erox
ide
of le
ad (
Pb02
), o
xyge
n ha
ving
bee
n
FIG
. are
leas
ed f
rom
the
dilu
te a
cid
by th
e "
char
ging
" cu
rren
t, an
d th
atup
on th
e ne
gativ
e pl
ate
or k
atho
de, f
irst
to a
low
er o
xide
and
then
tosp
ongy
lead
.T
he h
ydro
gen
evol
ved
at th
e ka
thod
e co
mbi
ned
with
the
sulp
hion
(SO
4)of
the
sulp
hate
of
lead
and
for
med
sul
phur
ic a
cid
(H2
SO4)
.
A m
ore
mod
ern
met
hod,
how
ever
, is
to f
orm
a p
aste
of
litha
rge
(Pb
0)an
d su
lphu
ric
acid
for
cov
erin
g th
e ne
gativ
e pl
ate,
as
the
amou
nt o
f en
ergy
requ
ired
to d
eoxi
dise
lith
arge
is le
ss th
an th
at n
eces
sary
to r
educ
e m
iniu
m,
whi
ch is
a h
ighe
r ox
ide.
116
RO
TE
S O
N T
EL
EG
RA
PHY
.
TH
E E
LE
CT
RIC
PO
WE
R S
TO
RA
GE
CE
LL
.
The
K7
E.P
.S. c
ell
is la
rgel
y us
ed b
y th
e Po
st O
ffic
e.T
he n
umbe
rof
pla
tes
empl
oyed
in th
is c
ell i
s se
ven,
fou
r of
whi
char
e ne
gativ
es a
ndth
ree
posi
tives
. The
latte
r ar
e co
mpa
rativ
ely
thic
k an
d gr
oove
d,as
sho
wn
in F
ig. 6
7.A
larg
e qu
antit
y of
the
past
e, w
hich
is a
com
poun
d of
min
ium
and
dilu
te s
ulph
uric
aci
d, c
an b
e w
orke
d in
to th
egr
oove
s.T
his
is a
n im
prov
emen
t upo
n th
e ol
der
type
of
plat
es, t
he s
urfa
ces
of w
hich
wer
e m
erel
y ro
ughe
ned.
Lith
arge
isad
ded
toth
e m
iniu
m a
nd
iFIG
. GS.
sulp
huri
cac
id u
pon
the
nega
tive
plat
es,
whi
chha
veho
les
inth
em w
ith p
roje
ctio
ns a
cros
s th
e ho
les,
sho
wn
in F
ig.
68, t
o ke
ep th
epa
ste
in p
ositi
on.
The
exc
ess
num
ber
of n
egat
ive
plat
es is
to e
nsur
ean
app
roxi
mat
e eq
ualit
y of
che
mic
al a
ctio
n up
on b
oth
side
s of
the
posi
tive
plat
es; "
buc
klin
g" o
f th
e pl
ates
, due
to a
n un
equa
l exp
ansi
on o
f th
e pa
stes
,an
d a
poss
ibili
ty o
f co
ntac
t bet
wee
n th
em a
re th
ereb
y av
oide
d, a
nd th
eir
mec
hani
cal s
tren
gth
is n
ot u
ndul
y re
duce
d.T
o pr
even
t the
act
ion
of th
eel
ectr
olyt
e up
on th
e pl
ates
or
grid
s, a
nd c
onse
quen
tly m
aint
ain
thei
rm
echa
nica
l str
engt
h, th
ey a
re f
requ
ently
allo
yed
with
10
per
cent
, of
antim
ony.
The
pos
itive
and
neg
ativ
e pl
ates
are
arr
ange
d al
tern
atel
y, th
eth
ree
form
er b
eing
con
nect
ed a
t the
top,
and
the
four
latte
r at
the
botto
mof
the
cell.
Thi
s m
etho
d of
join
ing
tend
s to
pro
duce
an
equa
lity
ofch
emic
al a
ctio
n.
For
the
obvi
ous
reas
on o
f re
duci
ng th
e re
sist
ance
of
the
cell,
whi
ch is
abou
t .00
15 o
hm, t
he p
late
s ar
e ke
pt a
s cl
osel
y to
geth
eras
pos
sibl
e,w
ithou
t bei
ng in
act
ual c
onta
ct ;
but s
uffi
cien
t spa
ce is
left
to a
llow
any
deta
ched
fra
gmen
ts o
f th
e pa
ste
to f
all c
lear
of
them
.O
ver
each
posi
tive
plat
ean
ebon
itefo
rkis
fitte
dto
keep
the
plat
es f
rom
act
ual c
onta
ct.
The
set
rest
s up
on a
pie
ce o
f H
-sha
ped
NO
TE
S O
N T
EL
EG
RA
PHY
.11
7
para
ffin
ed w
ood
plac
ed h
oriz
onta
lly a
t the
bot
tom
of
the
cell,
and
the
who
le is
pla
ced
into
a th
ick
glas
s ve
ssel
con
tain
ing
the
elec
trol
yte.
The
deta
ched
pie
ces
of p
aste
, etc
., fa
ll cl
ear
of th
e pl
ates
to th
e bo
ttom
of
the
glas
s ve
ssel
, and
this
is th
e ob
ject
for
res
ting
the
set u
pon
the
woo
den
stan
d.T
he u
se o
f gl
ass
as th
e co
ntai
ning
ves
sel e
nabl
es a
clo
se e
xam
ina-
tion
of th
e ce
ll to
be
easi
ly m
ade
and
a kn
owle
dge
of it
s ge
nera
l con
ditio
nto
be
read
ily a
scer
tain
ed.
Bot
h el
ectr
odes
may
be
past
ed w
ith s
ulph
ate
of le
ad (
Pb S
O4)
, mad
eof
a m
ixtu
re o
f re
d le
ad (
Pb50
4) a
nd s
ulph
uric
aci
d.T
he e
ffec
t of
" ch
argi
ng"
redu
ces
the
sulp
hate
of
lead
to s
pong
y le
ad a
t the
neg
ativ
epl
ate
and
lead
per
oxid
e at
the
posi
tive
plat
e.T
he s
ame
resu
lt is
als
oat
tain
ed w
hen
litha
rge
is e
mpl
oyed
.T
he "
for
med
" pl
ates
are
usu
ally
supp
lied
by th
e m
aker
s re
ady
for
char
ging
.T
he c
hem
ical
act
ion
whi
ch ta
kes
plac
e in
a s
econ
dary
cel
lis
ver
yco
mpl
icat
ed, b
ut m
ay b
e re
pres
ente
d by
thre
e ch
emic
al f
orm
ulte
, fro
mw
hich
it w
ill b
e se
en th
at th
e de
nsity
of
the
elec
trol
yte
grad
ually
incr
ease
sby
the
form
atio
n of
sul
phur
ic a
cid.
Bef
ore
the
cell
is c
harg
ed it
may
be
assu
med
that
the
plat
es a
re s
ulph
ate
of le
ad, a
nd th
at th
e liq
uid
is d
ilute
sulp
huri
c ac
id.
The
che
mic
al f
orm
ula
is th
en
[BE
FOR
E C
HA
RG
ING
]
Pb S
O4
+ 2
H2O
+ H
2 50
4.Pb
SO
4D
urin
g th
e pr
oces
s of
cha
rgin
g th
e w
ater
is d
ecom
pose
d in
to it
s co
nstit
uent
elem
ents
, the
act
ion
bein
g re
pres
ente
d th
us-
[WH
ILE
CH
AR
GIN
G]
Pb S
O4
+ 0
2 -I
- H
2 SO
, + 2
H2
Pb S
O4
Whe
n th
e ce
ll is
ful
ly c
harg
ed th
e su
lphi
on o
f th
e su
lpha
te o
f le
ad h
asen
tere
d in
to c
hem
ical
com
bina
tion
with
the
hydr
ogen
, res
ultin
g in
the
form
atio
n of
sul
phur
ic a
cid,
whi
le th
e ox
ygen
toge
ther
with
the
lead
at
the
anod
e ha
s pr
oduc
ed p
erox
ide
of le
ad.
The
for
mul
a m
ay b
e st
ated
thus
-[F
OL
LY
CH
AR
GE
D]
Pb 0
2 +
H2
SO4
+ H
2 SO
, + H
2 SO
4Pb
Sum
mar
ised
, the
chi
ef p
oint
s ab
out t
he "
acc
umul
ator
" a
re :-
Dur
ing
char
ging
, the
pos
itive
pla
te a
nd p
ole
of th
e se
cond
ary
cell
are
inco
nnec
tion
with
the
posi
tive
pole
of
the
prim
ary
gene
rato
r; th
e ne
gativ
epl
ate
and
pole
bei
ng, p
erfo
rce,
in c
onne
ctio
n w
ith th
e ne
gativ
e po
le o
f th
ege
nera
tor.
In d
isch
argi
ng, i
.e.,
whe
n th
e se
cond
ary
curr
ent i
s fl
owin
g, th
e sa
me
term
s ar
e em
ploy
ed, a
lbei
t the
act
ual c
ondi
tions
with
reg
ard
to th
e pl
ates
,ar
e re
vers
ed.
The
pol
es o
f th
e se
cond
ary
cell,
how
ever
, rem
ain
unal
tere
d,be
caus
e th
e cu
rren
t flo
ws
from
the
posi
tive
to th
e ne
gativ
e po
le.
118
NO
TE
S O
N T
EL
EG
RA
PHY
.
In th
e pr
oces
s of
" f
orm
ing
" th
e re
duct
ion
of th
epa
ste
to a
con
ditio
nof
spo
ngy
lead
is a
imed
at,
and
this
res
ults
ina
larg
er s
urfa
ce o
f ac
tive
mat
eria
l bei
ng c
reat
ed.
The
cel
l can
thus
be
very
hig
hly
" ch
arge
d,"
and
its c
apac
ity f
or s
tori
ng u
p th
e es
sent
ials
for
an
outp
ut o
f el
ectr
ical
ene
rgy
is c
onse
quen
tly m
ater
ially
incr
ease
d.In
the
Post
Off
ice
the
cells
are
join
edup
in r
ows
of c
onve
nien
t num
bers
for
the
purp
ose
of c
harg
ing
and
to g
ive
cert
ain
volta
ges.
For
char
ging
ther
e is
req
uire
d a
supp
ly o
fpo
wer
cap
able
of
givi
ng a
cur
rent
at a
slig
htly
high
er p
ress
ure
than
the
cells
to b
e ch
arge
d.T
his
supp
ly m
ay b
e fr
om o
ne o
f th
e fo
llow
ing
sour
ces,
viz
:-(a
) A
bat
tery
of
prim
ary
cells
.(b
) A
dyn
amo
driv
en b
y a
gas
or s
team
eng
ine.
(c)
A m
otor
-dy
nam
o dr
iven
by
pow
er f
rom
a s
uppl
y co
mpa
ny's
mai
ns,
the
curr
ent g
ener
ally
bei
ng a
n al
tern
atin
g on
e.(d
) Po
wer
obt
aine
d di
rect
fro
m th
e su
pply
com
pany
's m
ains
.T
he m
etho
ds n
amed
in b
and
c a
re th
ose
gene
rally
ado
pted
by
the
Bri
tish
Post
Off
ice.
In th
e ca
se o
f b
the
gas
engi
ne a
nd d
ynam
o m
ust h
ave
suff
icie
ntpo
wer
to g
ive
a pr
essu
re a
bout
25
per
cent
. gre
ater
than
the
elec
tro-
mot
ive
forc
eof
the
larg
est g
roup
whe
n th
e ce
lls a
re f
ully
cha
rged
.Fo
r ex
ampl
e, a
grou
p co
nsis
ting
of 2
5 ce
lls, w
hich
wou
ld h
ave
an e
lect
ro-m
otiv
e fo
rce
of62
.5 v
olts
whe
n ch
arge
d-th
e el
ectr
o-m
otiv
e fo
rce
of e
ach
fully
cha
rged
cell
bein
g 2.
5 vo
lts-w
ould
req
uire
to b
e ch
arge
d fr
oma
dyna
mo
capa
ble
of p
rodu
cing
a p
ress
ure
of a
bout
75
volts
.T
his
will
be
unde
rsto
od f
rom
the
follo
win
g :-
The
cel
ls a
re s
uppl
ied
by th
e m
anuf
actu
rers
alr
eady
"fo
rmed
," a
nd, o
nbe
ing
conn
ecte
d to
geth
er in
gro
ups
upon
the
rack
s, th
ey a
re c
harg
ed f
orth
e fi
rst t
ime
for
a pe
riod
of
abou
t 30
hour
s.D
urin
g th
at ti
me
the
curr
ent f
rom
the
sour
ce o
f su
pply
mus
t not
cea
se, e
xcep
t for
a ve
ry b
rief
peri
od to
oil
the
engi
ne a
nd d
ynam
o.T
he a
cid
is p
oure
d in
to th
e ce
lls b
efor
e ch
argi
ng a
nd th
edy
nam
ojo
ined
up
as s
how
n in
Fig
. 69.
Whe
n ch
argi
ng c
omm
ence
s, th
e el
ectr
o-m
otiv
e fo
rce
of a
n E
.P.S
. K7
cell
is a
bout
1.8
vol
t, w
hich
ris
es d
urin
g th
e fi
rst h
our
or s
o to
two
volts
,an
d af
terw
ards
ver
y sl
owly
unt
il 2.
4 or
'2.5
vol
ts is
obt
aine
d w
hen
the
cell
is f
ully
cha
rged
.D
urin
g th
e pr
oces
s of
cha
rgin
g th
e sp
ecif
ic g
ravi
ty o
f th
e el
ectr
olyt
eun
derg
oes
a ch
ange
.A
fter
a b
rief
per
iod
bubb
les
ofga
s ar
e ev
olve
d,an
d th
ese
incr
ease
in v
olum
e as
tim
ego
es o
n,un
tilth
eliq
uid
has
the
appe
aran
ce o
f m
ilk.
The
cel
ls a
re th
en a
ssum
ed to
be
fully
char
ged,
and
by
mea
ns o
f th
e vo
ltmet
er a
nd h
ydro
met
er th
eir
cond
ition
may
be
defi
nite
ly a
scer
tain
ed.
NO
TE
S O
N T
EL
EG
RA
PHY
.11
9
The
mak
ers
of s
econ
dary
cel
ls s
peci
fy th
e cu
rren
t whi
ch is
req
uire
dfo
r
char
ging
.In
the
case
of
E.P
.S. K
7 ce
lls th
e cu
rren
t mus
t be
betw
een
15an
d 25
am
pere
s.
1 -
FIG
. G9
From
thes
e fi
gure
s th
e am
ount
of
ener
gy n
eede
d ca
n be
cal
cula
ted
from
the
follo
win
g fo
rmul
a :-
E -
e
Whe
re C
= th
e cu
rren
t in
ampe
res.
E =
the
requ
ired
ele
ctro
-mot
ive
forc
e.e
= th
e el
ectr
o-m
otiv
e fo
rce
per
cell
at th
e st
art.
Ii =
the
resi
stan
ce o
f th
e ba
ttery
.A
ssum
ing
that
a c
harg
ing
curr
ent o
f 20
am
pere
s is
req
uire
dan
d th
ata
grou
p of
25
cells
is b
eing
cha
rged
the
equa
tion
beco
mes
CE
- (
25 x
e)
-T
he r
esis
tanc
e of
the
batte
ry, h
owev
er, i
sso
sm
all t
hat i
t may
be
negl
ecte
d, th
e eq
uatio
n th
en b
eing
20 =
E -
(25
x 1
.8)
2Q=
E -
45
E =
45
+ 2
0=
65
volts
.A
t the
com
men
cem
ent o
f ch
argi
ng th
e dy
nam
o m
ust b
e ru
nto
prod
uce
65 v
olts
.A
s th
e ch
argi
ng p
roce
eds,
how
ever
, the
bac
k el
ectr
o-m
otiv
e fo
rce
of th
e ce
lls in
crea
ses,
and
the
elec
tro-
mot
ive
forc
e of
the
dyna
mo
mus
t, co
nseq
uent
ly, b
e in
crea
sed.
Thi
s ca
n be
eff
ecte
d by
incr
easi
ng th
e sp
eed
of th
e ga
s en
gine
, or
the
curr
ent m
ay b
e au
gmen
ted
by c
uttin
g ou
t res
ista
nce
in th
e le
ads
betw
een
the
dyna
mo
and
the
cells
.T
he m
etho
d of
obt
aini
ng th
e re
quir
ed e
nerg
y fo
r ch
argi
ng, a
s in
dica
ted
inb,
is b
ecom
ing
obso
lete
,an
d w
here
ver
it is
pos
sibl
eto
obt
ain
the
ener
gy f
rom
a s
uppl
y co
mpa
ny th
e ga
s en
gine
is d
ispe
nsed
with
.
A m
otor
-dy
nam
o,ta
king
itspo
wer
from
asu
pply
com
pany
,is
subs
titut
ed, a
nd th
is s
yste
m is
rap
idly
com
ing
into
gen
eral
pra
ctic
e.
112
NO
TE
S O
N T
EL
EG
RA
PHY
.
Whe
n on
ly tw
o co
nden
sers
are
join
ed in
cas
cade
the
resu
ltant
cap
ityis
the
prod
uct o
f th
e se
para
te c
apac
ities
div
ided
by
thei
r su
m.
Exa
mpl
e 44
.-W
hat i
s th
e ca
paci
ty o
f tw
o co
nden
sers
join
ed in
cas
cade
,th
eir
sepa
rate
cap
aciti
es b
eing
res
pect
ivel
y th
ree
and
five
mic
ro -
fara
ds ?
Tot
al c
apac
ity =
x C
01 ±
3 x
53
+ 5
15 8
=
Ans
wer
:1Z
mic
ro -
fara
d.
Exa
mpl
e 45
.-T
he c
apac
ity o
f tw
o co
nden
sers
join
ed in
cas
cade
is .7
5m
icro
-fa
rad.
If th
e ca
paci
ty o
f on
e of
them
is th
ree
mic
ro -
fara
ds, w
hat i
sth
e ca
paci
ty o
f th
e ot
her
?
Tot
al c
apac
ity -
01 x
'4L
1 +
(%a
,75=
3 x
3 +
0,
Cro
ss m
ultip
lyin
g,3
C, =
2.25
+ .7
502
3 C
2 -
.75
C2
=2.
25
2.25
02
=2.
25
C, =
1
Ans
wer
:1
mic
ro -
fara
d.
Exa
mpl
e 46
.-W
hat i
s th
e ca
paci
tyof
thre
e co
nden
sers
join
edin
casc
ade,
if th
e se
para
te c
apac
i tie
s ar
e 2,
3, a
nd 4
mic
ro -
fara
ds r
espe
ctiv
ely
?
Tot
al c
apac
ity =
1
6 +
4 +
312
=12 13
Ans
wer
:12
mic
ro -
fara
d.13
NO
TE
S O
N T
EL
EG
RA
PHY
.11
8
CH
APT
ER
XV
.
TH
E S
EC
ON
DA
RY
CE
LL
.
The
theo
ry o
f th
e se
cond
ary
cell
or "
acc
umul
ator
"is
mor
e ea
sily
unde
rsto
od a
fter
a b
rief
sur
vey
of th
e G
rove
's g
as b
atte
ry.
In th
e de
scri
ptio
n of
the
sim
ple
cell
it w
as s
tate
d th
at "
pol
aris
atio
n "
quic
kly
depr
ived
the
cell
of it
s pr
actic
al u
se.
The
re e
xist
ed a
tend
ency
for
a ba
ck e
lect
ro-m
otiv
e fo
rce
to b
e se
t up,
con
sequ
ent u
pon
an a
ccum
u-la
tion
of th
e el
ectr
o-po
sitiv
e ra
dicl
e, h
ydro
gen,
upo
n th
e ne
gativ
e pl
ate.
In th
e se
cond
ary
cell,
how
ever
, the
eff
ect o
f po
lari
satio
n is
turn
ed to
aus
eful
acc
ount
, the
cur
rent
bei
ng d
ue to
the
coun
ter
elec
tro-
mot
ive
forc
ese
t up
as a
con
sequ
ence
of
cert
ain
chem
ical
cha
nges
taki
ng p
lace
in th
eoe
ll w
hen
an e
lect
ric
curr
ent f
rom
a p
rim
ary
sour
ce is
pas
sing
thro
ugh
it.
The
type
of
seco
ndar
y ce
ll in
vent
ed b
y G
rove
s co
nsis
ts o
f tw
o gl
ass
tube
s ha
ving
thei
r up
per
ends
clo
sed.
Into
the
clos
ed e
nd o
f ea
ch tu
be a
plat
inum
wir
e is
fus
ed, a
nd to
eac
h w
ire
a pl
atin
um s
trip
, whi
ch e
xten
dsto
the
base
of
the
tube
, is
atta
ched
.T
he tu
bes
are
fille
d w
ith w
ater
,a
little
acid
bei
ng a
dded
toin
crea
seits
cond
uctiv
ity, a
nd p
lace
dve
rtic
ally
into
a v
esse
l con
tain
ing
a si
mila
r liq
uid,
thei
r cl
osed
end
s be
ing
uppe
rmos
t.T
he f
ree
ends
of
the
wir
es a
re a
ttach
ed o
ne to
eac
h po
le o
fa
prim
ary
batte
ry, o
r an
y ot
her
gene
rato
r of
a f
airl
y st
rong
cur
rent
.T
hepa
ssag
e of
a c
urre
nt th
roug
h th
e w
ater
(H
20)
resu
lts in
the
latte
r be
ing
deco
mpo
sed
into
its
cons
titue
nt e
lem
ents
, H2
(hyd
roge
n) a
nd 0
(ox
ygen
).T
he h
ydro
gen
follo
ws
the
path
ofth
ecu
rren
t, an
dis
give
nof
fat
the
plat
inum
stri
pin
conn
ectio
nw
ith th
ezi
ncor
nega
tive
pole
of
the
prim
ary
batte
ry, w
hile
the
oxyg
en is
evo
lved
at t
he s
trip
con
-ne
cted
with
the
posi
tive
pole
of
the
prim
ary
batte
ry.
Hyd
roge
n is
ele
ctro
-po
sitiv
e to
oxy
gen
so th
at, w
hen
the
two
wir
es a
ttach
ed to
the
plat
inum
stri
ps a
re r
emov
ed f
rom
the
prim
ary
batte
ry a
nd jo
ined
to a
gal
vano
-m
eter
, a c
urre
nt f
low
s fr
om th
e hy
drog
en -
cove
red
stri
p th
roug
h th
e liq
uid
to th
e st
rip
at w
hich
the
oxyg
en is
evo
lved
, and
, if
the
galv
anom
eter
issu
ffic
ient
ly s
ensi
tive,
a d
efle
ctio
n is
obs
erve
d.
Thi
s se
cond
ary
curr
ent,
due
to th
edi
ffer
ence
of
pote
ntia
l exi
stin
gbe
twee
n th
e ga
ses,
is o
ppos
ite in
dir
ectio
n to
that
of
the
prim
ary
curr
ent,
and
it w
ill f
low
unt
il th
e se
para
ted
hydr
ogen
and
oxy
gen
have
re
-uni
ted
and
agai
n fo
rmed
wat
er.
The
two
plat
inum
str
ips
are
calle
d th
e "
elec
trod
es,"
and
the
liqui
d is
the
" el
ectr
olyt
e."
An
" el
ectr
olyt
e "
is a
com
poun
d w
hich
is th
us c
apab
leof
dec
ompo
sitio
n, a
nd "
ele
ctro
lytic
act
ion
" is
sai
d to
take
pla
ce w
hen
com
poun
d is
ele
ctri
cally
dec
ompo
sed.
122
NO
TE
S O
N T
EL
EG
RA
PHY
.
1,00
0, 9
00, 8
00,
700,
and
600
ohm
s re
sist
ance
resp
ectiv
ely
are
tobe
grou
ped.
The
res
ista
nce
repr
esen
ting
a25
per
cen
t. re
duct
ion
of 1
,000
ohm
s is
750
ohm
s, a
nd it
will
be
seen
that
the
circ
uits
havi
ng r
esis
tanc
es o
f 70
0 an
d 60
0 oh
ms
requ
ire
resi
stan
ce b
lock
s.T
hem
ean
betw
een
1,00
0 oh
ms
and
750
ohm
s is
875
ohm
s, a
nd to
this
val
ueth
e re
sist
ance
of
each
of
the
two
circ
uits
und
er c
onsi
dera
tion
shou
ld b
era
ised
.R
esis
tanc
es o
f 17
5 oh
ms
and
275
ohm
s sh
ould
, the
refo
re, b
ein
sert
ed in
the
batte
ry le
ads
of th
e 70
0 an
d 60
0 oh
ms
circ
uits
res
pect
ivel
y.W
hen
stan
dard
res
ista
nce
bloc
ks o
f th
e ex
act v
alue
can
not b
e ob
tain
ed,
the
near
est a
vaila
ble
shou
ld b
e us
ed.
In s
ingl
e cu
rren
t wor
king
one
pol
e of
the
batte
ry is
ear
thed
, and
the
circ
uits
are
so
grou
ped
that
" u
p "
and
" do
wn
" in
stru
men
ts a
re w
orke
dfr
om d
iffe
rent
batte
ries
.A
n "
inte
rmed
iate
" in
stru
men
t on
a si
ngle
curr
ent c
ircu
it ca
nnot
be
wor
ked
on th
e un
iver
sal b
atte
ry s
yste
m.
In th
eca
se o
f "
up "
inst
rum
ents
the
nega
tive
pole
of
the
batte
ry is
ear
thed
; w
ith
Lim
ef.
L;r
iE2.
LIN
E3.
-o
9
FIG
.70
" do
wn
" in
stru
men
ts th
e re
vers
e co
nditi
on p
reva
ils.
The
oth
er p
ole
inea
ch c
ase
is jo
ined
to th
e le
ft-h
and
term
inal
of
the
key
of e
ach
circ
uit,
and,
whe
re n
eces
sary
, res
ista
nce
bloc
ks a
re in
sert
ed b
etw
een
thes
e po
ints
.Fi
g. 7
0 sh
ows
the
batte
ry c
onne
ctio
nsfo
r "u
p "
offi
ce w
orki
ng, t
heba
lanc
ing
resi
stan
ce b
eing
sho
wn
in c
onne
ctio
n w
ith c
ircu
it 2.
Upo
n sy
stem
s in
whi
ch d
oubl
e cu
rren
t wor
king
is a
dopt
ed, a
nd u
pon
sing
lene
edle
and
dou
ble
-pla
te s
ound
er c
ircu
its,
itis
nece
ssar
y to
use
two
batte
ries
, eac
h of
whi
ch is
ear
th c
onne
cted
.T
he r
easo
n fo
r th
is w
ill b
ere
adily
see
n if
it is
rem
embe
red
that
whe
n on
ly o
ne b
atte
ry is
bei
ng u
sed,
and
one
key
is jo
inin
g th
e po
sitiv
e po
le to
ear
th w
hile
ano
ther
is c
onne
ctin
gth
e ne
gativ
e po
le to
ear
th, t
he b
atte
ry is
sho
rt-c
ircu
ited,
and
no
curr
ent
NO
TE
S O
N T
EL
EG
RA
PHY
.12
3
pass
es to
eith
er li
ne.
In p
ract
ice,
how
ever
, the
two
sets
ofce
lls a
rejo
ined
toge
ther
in s
erie
s, th
e ce
ntre
of
the
com
bine
d ba
ttery
bei
ng e
arth
conn
ecte
d.
For
doub
le -
curr
ent w
orki
ng u
pon
the
univ
ersa
l bat
tery
sys
tem
a s
ingl
ecu
rren
t key
fitt
ed w
ith a
sw
itch
is u
3ed.
Its
conn
ectio
ns w
ith th
esw
itch
in a
n in
term
edia
te p
ositi
on a
re in
dica
ted
in F
ig. 7
1.W
ith th
esw
itch
to "
sen
d "-
i.e.,
conn
ecte
d w
ith th
e le
ft-h
and
stop
,- a
nd th
e ke
yat
res
t, th
e fr
ont r
ight
-han
d te
rmin
al is
join
ed to
the
left
-ba
nd b
ack
term
inal
, whi
le th
e de
pres
sion
of
the
key
conn
ects
the
fron
t and
bac
kri
ght-
hand
term
inal
s.W
ith th
e sw
itch
in th
e "
rece
ive
" po
sitio
n, th
etw
o fr
ont t
erm
inal
s ar
e co
nnec
ted
via
the
switc
h, th
e ba
ttery
bei
ngdi
scon
nect
ed.
FIG
71.
" U
p "
and
" do
wn
" te
rmin
al s
ets
of a
ppar
atus
may
be
wor
ked
upon
the
doub
le c
urre
nt s
yste
m f
rom
the
sam
e ba
ttery
.T
he n
eces
sary
..con
nect
ions
are
sho
wn
in F
ig. 7
2."
Inte
rmed
iate
" a
ppar
atus
may
als
obe
gro
uped
with
" te
rmin
al "
set
s, b
ut a
res
ista
nce
bloc
k, to
mak
e th
e"
up "
and
" d
own
" se
ctio
ns o
f th
e lin
e ap
prox
imat
ely
equa
l in
resi
st-
ance
, sho
uld
be in
sert
ed in
the
side
hav
ing
the
smal
ler
resi
stan
ce.
Thi
sre
sist
ance
, whi
ch is
inde
pend
ent o
f th
e pr
evio
usly
men
tione
d ba
lanc
ing
resi
stan
ce, i
s ar
rang
ed to
be
in th
e "
send
ing
" ci
rcui
t onl
y, s
o th
at a
" re
ceiv
ed "
cur
rent
is n
ot a
ffec
ted
by it
.A
n or
dina
ry f
ive
term
inal
dou
ble
curr
ent k
ey is
use
dfo
r"
inte
rmed
iate
" a
ppar
atus
.T
he n
eces
sary
conn
ectio
ns a
re in
dica
ted
in F
ig. 7
3, th
e ap
para
tus
on th
e le
ft s
how
ing
the
arra
ngem
ent w
hen
the
" do
wn
" se
ctio
n of
the
line
has
the
smal
ler
124
NO
TE
S O
N T
EL
EG
RA
PHY
.
resi
stan
ce, w
hile
upo
n th
e ri
ght-
hand
sid
e of
the
diag
ram
the
equa
lisin
gre
sist
ance
is s
how
n in
the
" up
" li
ne.
Whe
n "
inte
rmed
iate
" a
ppar
atus
is g
roup
ed w
ith "
term
inal
" a
ppar
atus
eac
h se
ctio
n of
the
line
upon
whi
chth
e fo
rmer
is in
sert
ed s
h,ul
d be
app
roxi
mat
ely
equa
l to
the
resi
stan
ce o
fth
e te
rmin
ated
line
s.
For
univ
ersa
l wor
king
upo
n du
plex
oir
cuits
a r
e -a
rran
gem
ent o
f th
eco
nnec
tions
is n
eces
sary
on
acco
unt o
f th
e ea
rth
conn
ectio
n at
the
batte
ry.
The
pri
ncip
le o
f th
e sy
stem
of
diff
eren
tial d
uple
x w
orki
ng, h
owev
er, i
s
UP
LIN
ED
OW
N L
INE
unal
tere
d, a
nd th
e st
uden
t who
has
mas
tere
d th
e du
plex
sys
tem
alr
eady
desc
ribe
d w
ill f
ind
no d
iffi
culty
in tr
acin
g th
e cu
rren
ts a
nd u
nder
stan
ding
how
the
cond
ition
s ne
cess
ary
for
dupl
ex w
orki
ng a
re b
roug
ht a
bout
. Fig
. 74
show
s th
e th
eore
tical
con
nect
ions
for
dup
lex
wor
king
at "
up
" an
d "
dow
n "
stat
ions
.Fo
r do
uble
pla
te s
ound
er a
nd s
ingl
e ne
edle
inst
rum
ents
the
sam
e un
derl
ying
pri
ncip
les
appl
y as
for
dou
ble
curr
ent w
orki
ng.
At
term
inal
off
ices
, how
ever
, pre
caut
ions
mus
t be
take
n to
pre
vent
the
batte
rybe
ing
shor
t-ci
rcui
ted
if b
oth
tapp
ers
be a
ccid
enta
lly d
epre
ssed
at t
he s
ame
time.
Thi
s is
eff
ecte
d by
a m
odif
icat
ion
of th
e co
mm
utat
or.
The
fro
ntco
ntac
t scr
ew o
f th
e le
ft-h
and
tapp
er is
rem
oved
, and
the
back
rig
ht-h
and
NO
TE
S O
N T
EL
EG
RA
PHY
.12
5
spri
ng is
dis
pens
ed w
ith, o
r so
adj
uste
d as
to p
reve
nt c
onta
ct b
eing
mad
ew
hen
the
righ
t-ha
nd ta
pper
is d
epre
ssed
.
At o
ffic
es w
here
sec
onda
ry c
ells
are
em
ploy
ed a
ll th
e ci
rcui
tsar
e w
orke
dup
on th
e un
iver
sal b
atte
ry p
rinc
iple
.T
hese
cel
ls a
re s
peci
ally
ada
pted
for
this
sys
tem
on
acco
unt o
f th
eir
exce
edin
gly
low
res
ista
nce,
and
not
only
are
they
use
d fo
r su
pply
ing
curr
ents
for
the
lines
but
for
the
loca
lba
ttery
cir
cuits
as
wel
l.Pr
actic
ally
the
who
le o
f th
e po
wer
req
uire
d fo
ran
y pu
rpos
e w
hate
ver
is o
btai
ned
from
the
sam
e se
t of
cells
.
The
chi
ef f
eatu
res
of a
n in
stal
latio
n of
sec
onda
ry c
ells
are
as
follo
wT
he s
tora
ge c
apac
ity o
f th
e ce
lls is
fix
ed in
acc
ord
with
the
wor
kre
quir
ed
UP
Lts
ieD
own
LIN
E
of th
em.
Itis
gen
eral
ly o
f 45
or
72 a
mpe
re h
ours
, i.e
., th
e cu
rren
t in
ampe
res
mul
tiplie
d by
the
time
in h
ours
.In
som
e ca
ses
the
mai
ns a
re 4
5an
d th
e lo
cals
72
ampe
ra h
ours
-the
loca
ls b
eing
the
hard
er w
orke
d of
the
two.
For
very
larg
e of
fice
s th
e m
ain
batte
ries
may
be
72 a
mpe
re h
ours
and
the
loca
ls s
till h
ighe
r.
The
mai
n ba
tteri
es, w
hich
giv
e vo
ltage
s of
40,
80,
and
120
, pos
itive
and
nega
tive,
are
pro
vide
d, to
geth
er w
ith a
loca
l set
of
24 v
olts
.T
he la
tter
also
pro
vide
s th
e w
orki
ng c
urre
nts
for
shor
t lin
es, a
nd, b
eing
a d
oubl
e se
t
126
NO
TE
S O
N T
EL
EG
RA
PHY
.
with
an
eart
h co
nnec
tion
at th
e ce
ntre
, the
rel
ay is
als
oea
rthe
d.T
hem
ain
batte
ries
are
arr
ange
d in
six
grou
ps o
f 20
cel
ls, a
nd a
re p
lace
d up
onra
cks
of d
imen
sion
s su
itabl
e to
take
two
grou
ps in
a "
bay
"-o
ne g
roup
on to
p an
d th
e ot
her
belo
w.
The
loca
ls a
ro in
fou
r se
ts o
f tw
elve
cel
ls e
ach,
so
that
whe
non
e do
uble
set (
24 c
ells
) is
in u
se a
noth
er d
oubl
e se
t is
bein
g he
ld in
rese
rve.
A f
ewsp
are
cells
are
kep
t asi
de to
rep
lace
any
whi
ch m
ay b
ecom
e de
fect
ive.
DO
WN
LIN
E
FOC
. 74.
UP
LIN
E
An
arra
ngem
ent o
f th
e vo
ltage
s fr
eque
ntly
ado
pted
is s
how
n in
Fig
.75
,it
bein
g un
ders
tood
, of
cour
se, t
hat s
imila
r se
ts o
f ce
lls a
re e
ither
lyin
gid
le o
r be
ing
char
ged,
As
the
inne
r se
ts o
f m
ain
cells
are
the
hard
est
wor
ked,
bei
ng th
ose
from
whi
ch th
e m
ost c
urre
nt is
dra
wn,
they
are
liabl
e to
bec
ome
exha
uste
d so
oner
than
the
oute
r se
ts.
By
mea
ns o
f a
switc
h th
e re
lativ
e po
sitio
ns o
f th
e ce
lls m
ay b
e va
ried
per
iodi
cally
and
NO
TE
S O
N T
EL
EG
RA
PHY
.12
7
the
actio
n of
all
the
sets
equ
alis
ed.
Ano
ther
sw
itch
is a
lso
empl
oyed
whi
ch, w
hile
join
ing
up th
e on
e se
t of
cells
for
use
in th
e in
stru
men
tro
om, l
eave
s th
e ot
her
set c
onne
cted
with
the
dyna
mo
for
char
ging
and
rem
oves
the
cent
ral e
arth
con
nect
ion.
Dis
trib
utin
g ca
bine
ts a
re p
rovi
ded
both
for
the
batte
ry r
oom
and
the
inst
rum
ent r
oom
, and
in th
e la
tter
room
tabl
e di
stri
butin
g bo
xes
are
also
arr
ange
d.O
ne b
ox s
uppl
ies
thre
eta
bles
, so
that
, sta
rtin
g fr
om o
ne e
nd o
f th
e ro
om, t
he f
irst
thre
e ta
bles
are
supp
lied
from
a b
ox o
n ta
ble
2; ta
bles
4, 5
, and
6 f
rom
a b
ox o
n ta
ble
5, a
nd s
o on
.A
ll th
e vo
ltage
s ar
e le
d to
eac
h bo
x, a
nd p
rovi
sion
is m
ade
for
the
conn
ectio
n of
ten
circ
uit l
eads
.
At e
very
cir
cuit,
or
at th
e ta
ble
dist
ribu
ting
boxe
s, a
one
-am
pere
fus
e is
plac
ed in
eac
h ba
ttery
lead
.Su
itabl
e fu
ses
are
also
pro
vide
d fo
r ea
ch
12.0
i
80'1
LO
CA
L
40./
1111
461
+
etr JA
I
MA
INB
fIT
TE
Ry
FIG
: 75
volta
ge a
t the
dis
trib
utin
g ca
bine
ts in
the
inst
rum
ent a
nd b
atte
ry r
oom
s.T
he o
bjec
t of
the
fuse
s is
to p
reve
nt th
e ex
haus
tion
of th
e ba
ttery
thro
ugh
" sh
ort-
circ
uit,"
and
als
o to
pro
tect
the
inst
rum
ents
fro
m th
e da
mag
ew
hich
wou
ld a
rise
fro
m th
e pa
ssag
e of
cur
rent
s of
exc
essi
ve s
tren
gth
thro
ugh
the
coils
.
Prec
autio
ns a
lso
mus
t be
take
n to
pre
vent
the
batte
ry d
isch
argi
ngth
roug
h th
e dy
nam
o sh
ould
the
latte
r be
acc
iden
tally
sto
pped
.T
he p
ro-
visi
on o
f a
suita
ble
" cu
t-ou
t" s
witc
h an
d fu
se e
nsur
es th
e br
eaki
ng o
f th
em
ain
circ
uit a
nd le
avin
g th
e ba
ttery
insu
late
d w
hen
the
disc
harg
e cu
rren
tfl
ows
from
the
cells
.
120
NO
TE
S O
N T
EL
EG
RA
PHY
.
CH
APT
ER
XV
I.
TH
E U
NIV
ER
SAL
BA
TT
ER
Y S
YST
EM
.
Whe
n a
larg
e nu
mbe
r of
wir
es r
adia
te f
rom
an
offi
ce th
ere
are
man
yve
ry o
bvio
us r
easo
ns w
hy th
e us
e of
a s
epar
ate
batte
ry f
or e
ach
circ
uit
shou
ld b
e av
oide
d. I
n ce
rtai
n ci
rcum
stan
ces,
in f
act,
one
batte
rypr
ovid
L s
the
nece
ssar
y cu
rren
t for
sev
eral
cir
cuits
.T
he la
tter,
how
ever
, hav
eap
prox
imat
ely
equa
l res
ista
nces
, and
, wha
t is
of g
reat
er im
port
ance
, the
resi
stan
ce o
f th
e fo
rmer
is c
ompa
rativ
ely
low
.
The
lim
itatio
n of
the
num
ber
of c
ircu
its w
hich
can
bo
adva
ntag
eous
lyw
orke
d fr
om th
e sa
me
batte
ry d
epen
ds u
pon
the
resi
stan
ce o
f th
ece
lls,
and
is b
est d
emon
stra
ted
by m
athe
mat
ical
exa
mpl
es.
If th
e ba
ttery
has
a ne
glig
ible
res
ista
nce
an u
nlim
ited
num
ber
of c
ircu
its c
an b
e w
orke
dfr
om it
, with
out i
n an
y w
ay r
educ
ing
the
amou
nt o
f cu
rren
tpe
r ci
rcui
t,w
here
as w
ith a
com
para
tivel
y hi
gh b
atte
ry r
esis
tanc
e a
prac
tical
lim
it is
quic
kly
reac
hed.
Firs
t sup
pose
that
the
batte
ry r
esis
tanc
e is
inap
prec
iabl
e an
d th
at th
eel
ectr
o-m
otiv
e fo
rce
is 5
0 vo
lts ;
ther
e ar
e te
n ci
rcui
ts c
onne
cted
to th
eba
ttery
and
eac
h ci
rcui
t res
ista
nce
is 1
,000
ohm
s.
Whe
n on
ly o
ne o
irou
it is
bei
ng w
orke
d :-
50 x
100
0C
-=
50
mill
iam
pere
s.10
00
With
two
circ
uits
wor
king
the
lines
are
join
ed in
mul
tiple
arc
and
the
tota
l res
ista
nce
is r
educ
ed to
500
ohm
s.C
onse
quen
tly th
e st
reng
thof
the
curr
ent o
btai
ned
from
the
batte
ry is
dou
bled
.
50 x 50
01000
C=
100
m.a
.
But
as
the
curr
ent w
ill d
ivid
e eq
ually
thro
ugh
the
two
circ
uits
, the
irre
sist
ance
s be
ing
equa
l, ea
ch c
ircu
it w
ill g
et 5
0 m
illia
mpe
res,
or
the
sam
ecu
rren
t as
whe
n on
ly o
ne c
ircu
it w
as w
orki
ng.
If w
e ta
ke f
ive
of th
e ci
rcui
ts, e
ach
draw
ing
its s
uppl
y of
cur
rent
from
the
sam
e so
urce
, the
ext
erna
l res
ista
nce
will
be
only
200
ohm
s, a
nd
50 x
100
0C
-20
0-
250
m.a
.
Aga
in th
e di
visi
on o
f th
e cu
rren
t res
ults
in e
ach
circ
uit g
ettin
g its
ful
l.A
are
of 5
0 no
illia
rapO
cs.
NO
TE
S O
N T
EL
EG
RA
PHY
.12
1
No
batte
ry,
how
ever
,is
devo
id o
f re
sist
ance
,an
d th
eco
nditi
ons
enum
erat
ed a
bove
are
pur
ely
hypo
thet
ical
.If
we
cons
ider
the
sam
eci
rcui
ts a
nd th
e sa
me
batte
ry, b
ut a
ssum
e th
atth
ela
tter
has
are
sist
ance
of,
say
, 50
ohm
s, it
will
be
seen
that
as
the
num
ber
of w
orki
ngci
rcui
ts in
crea
ses,
so
will
the
curr
ent a
ppro
pria
ted
by e
ach
dim
inis
h.
With
one
cir
cuit
wor
king
:- 50 x
1,0
00_
471.
1 m
.a.
C -
1,00
0 +
50
With
two
circ
uits
wor
king
sim
ulta
neou
sly
:-
=50
x 1
,000
_ 90
13 m
.a.
500
+ 5
0or
, 451
5f m
illia
mpe
res
for
each
cir
cuit.
With
fiv
e ci
rcui
ts w
orki
ng :-
C -
50 x
1 0
0020
0o0
- 20
0 m
.a.
or, o
nly
40 m
illia
mpe
res
for
each
cir
cuit.
The
low
er th
e re
sist
ance
of
the
batte
ry, t
hen,
the
grea
ter
the
num
ber
of c
ircu
its w
hich
can
be
grou
ped,
and
ifth
e ba
ttery
res
ista
nce
is
appr
oxim
atel
y eq
ual t
o ha
lf th
e jo
int r
esis
tanc
e of
the
circ
uits
a p
ract
ical
syst
em c
an b
e es
tabl
ishe
d.B
ichr
omat
e ce
lls a
re b
ette
r ad
apte
d fo
r"
univ
ersa
l " w
orki
ng th
an e
ither
Dan
iell
or L
ecla
nche
cel
ls.
As
the
form
er h
ave
a co
mpa
rativ
ely
high
ele
ctro
-mot
ive
forc
e an
d a
low
resi
stan
ceth
eyar
eve
rysu
itabl
efo
rth
epr
oduc
tion
ofhe
avy
curr
ents
.T
he n
umbe
r of
cir
cuits
gro
uped
toge
ther
whe
n th
e cu
rren
t is
obta
ined
fro
m a
pri
mar
y ba
ttery
is u
sual
ly n
ot m
ore
than
fiv
e.T
he
circ
u;,
mus
t hav
e ap
prox
imat
ely
the
sam
e re
sist
ance
to e
nsur
e ea
chge
tting
its
prop
er a
mou
nt o
f cu
rren
t.T
heir
leng
ths
also
sho
uld
not
diff
erto
any
gre
at e
xten
t, as
the
insu
latio
n re
sist
ance
of
the
long
erci
rcui
ts w
ill s
how
a g
reat
er v
aria
tion
inw
et w
eath
er th
an th
at o
fth
esh
orte
rlin
os.
Ifth
eci
rcui
tsar
eof
near
lyth
esa
me
leng
th c
limat
icin
flue
nces
will
affe
ct th
em e
qual
ly, a
nd th
e re
sult-
ing
fluc
tuat
ions
in th
e re
sist
ance
s w
ill n
ot m
ater
ially
aff
ect
the
wor
king
of th
e sy
stem
.T
he lo
wes
t res
ista
nce
shou
ld b
e no
t mor
e th
an 2
5 pe
rce
nt. l
ess
than
the
high
est.
In c
ases
whe
re a
gre
ater
dis
pari
ty th
an th
isex
ists
res
ista
nce
bloc
ks a
re in
trod
uced
into
the
batte
ry le
ads
of th
e lo
wre
sist
ance
cir
cuits
.T
he m
etho
d of
cal
cula
ting
the
nece
ssar
y ba
lanc
ing
resi
stan
ceis
to ta
keth
e m
ean
betw
een
the
high
est r
esis
tanc
e an
dth
at w
hich
is 2
5 pe
r ce
nt. l
ess
than
the
high
est,
and
leve
l up
the
resi
stan
ces
of th
e ci
rcui
ts w
hich
fal
l bel
ow th
e 25
per
cen
t. re
duct
ion
toth
e m
ean
resi
stan
ce.
For
exam
ple,
sup
pose
that
fiv
e ci
rcui
ts h
avin
g
130
NO
TE
% O
N T
EL
EG
RA
PHY
.
term
inat
ion
of th
e sp
acin
g cu
rren
t, th
eup
per
cont
act j
oins
up
the
othe
rpo
le o
f th
e ba
ttery
and
a s
hort
-cir
cuit
of th
e ce
llsen
sues
.If
this
mom
enta
ry s
hort
-cir
cuit
occu
rs d
urin
g th
e de
pres
sion
of
the
"B
" k
ey,
and
cons
eque
nt a
ctio
n of
the
who
le o
fth
e ba
ttery
, the
eff
ect i
s to
prod
uce
a "
kick
" in
the
" B
" r
elay
at t
here
ceiv
ing
end
of th
e ci
rcui
t.T
heco
nditi
ons,
of
cour
se, a
re th
e sa
me
if th
e re
vers
al o
fcu
rren
t is
bein
g m
ade
from
" m
arki
ng "
to "
spa
cing
."T
he e
ffec
t of
this
" k
ick"
bas
bee
npr
actic
ally
cou
nter
acte
d by
the
intr
oduc
tion
of a
"re
layi
ng "
or
" up
righ
t-in
g "
soun
der
betw
een
the
rela
y an
d th
ere
adin
g so
unde
r. T
he n
on -
pola
rise
dre
lay,
too,
is r
athe
r sl
uggi
sh in
actio
n, a
nd th
e co
mbi
ned
effe
ctis
suc
h as
toel
imin
ate
from
the
read
ing
soun
der
the
mom
enta
ry b
reak
in th
e si
gnal
.T
he r
elay
ing
soun
der
also
per
form
s us
eful
serv
ice
in a
noth
er d
irec
tion.
In th
e no
rmal
sta
te o
f af
fair
s th
eto
ngue
of
the
" B
" r
elay
is h
eld
byth
e an
tago
nist
ic s
prin
g ag
ains
t the
con
tact
scre
w w
hich
join
s up
the
loca
l bat
tery
con
nect
ed w
ith th
ere
layi
ng s
ound
er.
As
long
as
this
cond
ition
pre
vails
a c
urre
nt f
low
s th
roug
h th
eco
ils o
f th
e la
tter,
and
con
se-
quen
tly th
e ar
mat
ure
is a
ttrac
ted
tow
ards
the
pole
piec
es.
The
pas
sage
of
acu
rren
t thr
ough
the
rela
y co
ils o
f su
ffic
ient
stre
ngth
to m
erel
y br
eak
this
cont
act c
ause
sth
e ar
mat
ure
of th
e re
layi
ng s
ound
erto
be
rele
ased
.T
his
resu
lts in
the
read
ing
soun
der
bein
g ac
tuat
edby
vir
tue
of th
eco
ntac
t mad
e at
the
uppe
r sc
rew
of
the
rela
ying
sou
nder
, the
con
tact
bein
g ef
fect
ed w
ith th
e fu
ll fo
rce
of th
e la
tter's
adju
stin
g sp
ring
.It
will
be r
eadi
ly u
nder
stoo
d, th
eref
ore,
that
bet
ter
effe
cts
are
prod
uced
by
this
mea
ns th
anif
a co
ntac
t had
to b
e m
ade
agai
nst t
he f
orce
of
the
stro
ng a
ntag
onis
tic s
prin
g of
the
" B
" r
elay
.
The
pri
ncip
le o
f th
e qu
adru
plex
syst
em is
bas
ed u
pon
that
of
the
diff
eren
tial d
uple
x sy
stem
.T
he c
urre
nt s
plits
at t
he "
B "
rela
y, a
nd o
nepo
rtio
n pa
sses
thro
ugh
one
coil
of e
ach
of th
e re
lays
and
one
coil
of th
edi
ffer
entia
lly w
ound
gal
vano
met
er to
the
" ea
rthe
d "
artif
icia
lci
rcui
t,w
hich
is a
djus
ted
as f
or d
uple
x w
orki
ng. T
he o
ther
port
ion
of th
e cu
rren
ttr
aver
ses
the
othe
r co
ils o
f th
e re
lays
and
galv
anom
eter
,and
then
ce to
the
line.
The
arr
ange
men
t sho
wn
in F
ig. 7
6 is
for
an "
up
" of
fice
.T
he o
nly
alte
ratio
ns n
eces
sary
at a
" d
own"
off
ice
are
the
reve
rsal
of
the
wir
esjo
ined
to th
e lo
wer
term
inal
s of
the
galv
anom
eter
and
the
batte
ry le
ads.
A s
kele
ton
diag
ram
indi
catin
g th
e co
nnec
tions
at "
up"
and
" do
wn
"of
fice
s is
sho
wn
in F
ig. 7
7. T
his
will
pro
babl
y as
sist
the
stud
ent i
n un
der-
stan
ding
the
follo
win
g br
ief
expl
anat
ion
of th
e va
riou
s co
nditi
ons
whi
chha
ve to
be
met
in q
uadr
uple
x w
orki
ng :-
1. A
LL
KE
YS
AT
RE
ST.-
The
sm
all b
atte
ries
only
are
in o
pera
tion
and
curr
ents
fro
m b
oth
trav
erse
the
line
circ
uit i
n th
esa
me
dire
ctio
n.T
hepr
epon
dera
ting
curr
ent f
rom
the
com
bine
d ba
tteri
espa
sses
thro
ugh
both
" A
" r
elay
s in
a s
paci
ng d
irec
tion,
and
no s
igna
l is
reco
rded
. The
eff
ectiv
ecu
rren
ts p
assi
ng th
roug
h th
e "
B "
rel
ays,
i.e
, the
dif
fere
nce
betw
een
the
NO
TE
S O
N T
EL
EG
RA
PHY
.13
1
'turr
et&
flo
win
g in
the
artif
icia
l and
line
cir
cuits
, are
too
wea
l to
over
.m
une
the
anta
goni
stic
spr
ings
, and
the
rela
ys a
re n
ot a
ctua
ted.
C)
SI,
I !m
u "
A "
KE
YS
DE
PRE
SSE
D.-
The
cur
rent
s ar
eno
w r
ever
sed
and
Lls
o pr
epon
dera
ting
curr
ents
are
in th
e di
rect
ion
topr
oduc
e m
arki
ng
F2
122
NO
TE
S O
N T
EL
EG
RA
PHY
.
effe
cts
in b
oth
" A
" r
elay
s. T
he r
ever
sal o
f th
ecu
rren
t doe
s no
t aff
ect
the
" B
" r
elay
s.
3. A
LL
KE
YS
DE
PRE
SSE
D. -
The
con
ditio
nsar
e as
in c
ase
2, e
xcep
t tha
tth
e st
reng
ths
of th
e cu
rren
tsar
e in
crea
sed
by th
e ad
ditio
n of
the
" B
"ba
tteri
e3.
The
"B
" r
elay
s no
w a
lso
resp
ond,
how
ever
, by
virt
ue o
f a
grea
ter
prep
onde
ratin
g cu
rren
t in
the
line
circ
uit.
4. "
A "
KE
Y A
ND
" B
" K
EY
DE
PRE
SSE
DA
T D
IFFE
RE
NT
OFF
ICE
S.-
Supp
ose
that
the
" up
" o
ffic
e "
A "
key
and
the
" do
wn
" of
fice
" B
"ke
yar
e de
pres
sed.
In th
e lin
e ci
rcui
t the
cur
rent
fro
m th
eco
mbi
ned
" A
"an
d "
B "
bat
teri
es a
t the
" d
own
" of
fice
isop
pose
d by
the
smal
ler
curr
ent
from
the
" A
" b
atte
ry a
t the
"up
" of
fice
.T
he c
urre
nt f
rom
the
com
-bi
ned
batte
ries
at t
he "
dow
n "
stat
ion
isap
prox
imat
ely
thre
e tim
es a
sst
rong
as
that
fro
m th
e "
A "
bat
tery
at t
he "
up"
off
ice,
cons
eque
ntly
the
resu
ltant
cur
rent
in th
e lin
e ci
rcui
t is
twic
eas
str
ong
as th
at tr
aver
sing
the
artif
icia
l cir
cuit
at th
e "
up"
offi
ce.
The
dir
ectio
nof
the
pre-
pond
erat
ing
curr
ent t
hrou
gh th
e "
up"
offi
ce"
A "
rela
y pr
oduc
esa
spac
ing
effe
ct.
Now
con
side
r th
e ac
tion
of th
e cu
rren
tsup
on th
e "
B "
rela
y at
the
" up
"of
fice
.T
he c
urre
nt p
assi
ng to
the
artif
icia
l cir
cuit,
i.e.,
at th
e "
split
" o
f th
e re
lays
fro
m le
ft to
rig
ht, i
s fr
omth
e "
A "
batte
ry o
nly,
and
it tr
aver
ses
one
coil.
The
line
cur
rent
pas
ses
thro
ugh
the
othe
r co
il of
the
" B
" r
elay
, and
this
is a
lso
ina
dire
ctio
n fr
om le
ftto
rig
ht.
The
mag
netic
eff
ects
con
sequ
ently
com
bine
, the
resu
lt be
ing
that
the
arm
atur
e is
act
uate
d ag
ains
t the
for
ce o
f th
ean
tago
nist
ic s
prin
g.A
t the
" d
own
" of
fice
the
curr
ent i
s fr
om th
e co
mbi
ned
"A
" a
nd "
B "
batte
ries
, and
that
whi
ch p
asse
s to
the
artif
icia
l cir
cuit
isgr
eate
r in
stre
ngth
than
that
in th
e lin
e ci
rcui
t, as
the
latte
r is
wea
kene
dby
the
oppo
sitio
n of
the
curr
ent f
rom
the
" A
" b
atte
ry a
t the
"up
" st
atio
n.A
com
pari
son
of th
e st
reng
th o
f th
e tw
o cu
rren
tspa
ssin
g th
roug
h th
ere
lays
of
the
" do
wn
" of
fice
sho
ws
them
to b
e in
the
prop
ortio
n of
thre
eto
two,
and
the
diff
eren
ce b
etw
een
thei
rst
reng
ths
is n
ot s
uffi
cien
tly g
reat
to c
ause
the
" B
" r
elay
to b
e ac
tuat
ed.
The
" A
" r
elay
at t
he "
dow
n "
offi
ce, h
owev
er, w
ill r
espo
nd to
the
prep
onde
ratin
g cu
rren
t in
the a
rtif
icia
lci
rcui
t.T
his
curr
ent p
asse
s th
roug
h th
e "
A "
rela
y in
a d
irec
tion
from
righ
t to
left
, and
a m
arki
ng e
ffec
t, w
hich
is in
acc
ord
with
the
depr
essi
onof
the
" A
" k
ey a
t the
" u
p "
offi
ce,
is r
egis
tere
d in
that
rel
ay.
If th
e"
B "
key
at t
he "
up "
off
ice
an!
the
" A
" k
ey a
t the
" d
own
" of
fice
be
sim
ulta
neou
sly
depr
esse
d, b
y s
mila
r re
ason
ing
it w
ill b
ese
en th
at th
eco
rres
pond
ing
rela
ys w
ill b
e ac
tuat
ed.
The
con
stru
ctio
n of
the
non
-pol
aris
ed r
elay
requ
ires
a b
rief
des
crip
tion.
Thi
s re
lay
is p
rovi
ded
with
two
tong
ues
or a
rmat
ures
of
soft
iron
nor
mal
lyun
mag
netis
ed, a
s no
per
man
ent m
agne
t is
used
.A
cur
rent
in e
ither
dire
ctio
n th
roug
h th
e co
ils w
ill c
onse
quen
tlyca
use
the
arm
atur
es to
be
attr
acte
d an
d pr
oduc
e a
mar
king
eff
ect.
Cle
arly
, thi
s in
stru
men
t on
that
NO
TE
S O
N T
EL
EG
RA
PHY
.18
3
amou
nt w
ould
be
usel
ess
upon
ado
uble
curr
ent s
yste
m, b
ut it
is h
ighl
yad
apte
d to
the
cond
ition
s up
on th
e "
B "
sid
e of
the
quad
rupl
ex c
ircu
it.A
spe
cial
kin
d of
non
-po
lari
sed
rela
y, h
owev
er, i
s us
ed in
this
cas
e. T
he tw
oar
mat
ures
are
piv
oted
at t
heir
cer
tres
, the
two
sect
ions
of
each
bei
ng b
raze
dto
geth
er b
y a
non-
mag
netic
sub
stan
ce in
the
sam
ew
ay a
s Sp
agno
letti
'sne
edle
. Thi
s ar
rang
emen
t pre
vent
sa
clos
ed m
agne
tic c
ircu
it be
ing
form
edbe
twee
n th
ese
and
the
pole
s of
the
elec
tro-
mag
nets
, whe
n at
trac
tion
ofea
ch s
ectio
n of
bot
h ar
mat
ures
tow
ards
the
near
est p
ole
-pie
ce ta
kes
plac
e.A
clo
sed
mag
netic
cir
cuit
wou
ldco
nsid
erab
ly in
crea
se th
e se
lf-i
nduc
tion
of th
e el
ectr
o-m
agne
t and
act
dele
teri
ousl
y up
on th
e ra
te o
f w
orki
ng.
The
key
s ar
e w
ithou
t sw
itche
s, b
ut in
ord
er th
at th
e lin
em
ay b
e pu
t to
eart
h fo
r ba
lanc
ing
purp
oses
, etc
., a
switc
h is
pla
ced
betw
een
the
" A
"ke
y an
d th
e sp
lit o
f th
e "B
" r
elay
.B
y tu
rnin
g th
e sw
itch
to th
e ri
ght
the
mai
n ba
tteri
es a
re c
ut o
ut o
f th
e lin
eci
rcui
t, an
d w
aste
of
ener
gy m
aybe
pre
vent
ed w
hen
the
appa
ratu
s is
not
req
uire
d fo
r us
e.A
s th
e re
lays
tio
To
.73
Ye
/Iv
.
4111
1
FIG
. 78.
rem
ain
in c
ircu
it, h
owev
er, s
igna
lsfr
om th
e di
stan
t sta
tion
may
be
rece
ived
, and
atte
ntio
n ga
ined
.O
n th
e ea
rth
side
of
the
switc
h a
resi
st-
ance
is in
sert
ed.
It is
app
roxi
mat
ely
equa
l to
that
of
the
who
le b
atte
ryan
d th
e sp
ark
coil.
The
latte
r is
sho
wn
on th
e ri
ght o
f th
e "
B "
key
, in
loig
.76
.T
he s
park
coi
l pre
vent
s da
mag
e to
the
cont
act p
oint
s w
hen
Hie
who
le b
atte
ry is
mom
enta
rily
sho
rt-c
ircu
ited.
The
res
ista
nce
inse
rted
at th
e le
ft-h
and
term
inal
of
the
" B
" k
ey is
app
roxi
mat
ely
equa
l to
both
that
of th
e la
rger
sec
tion
of th
e ba
ttery
and
the
spar
k co
il. T
his
prev
ents
any
vari
a-tio
n in
the
resi
stan
ce o
f th
e ci
rcui
t whe
n th
e ke
ys a
re b
eing
man
ipul
ated
.
For
univ
ersa
l wor
king
a s
peci
al a
rran
gem
ent o
f th
e ke
ys is
nece
ssar
y on
wir
ount
of
the
eart
h co
nnec
tion
at th
e ba
ttery
.T
his
is s
how
n in
Fig
. 78
131
NO
TE
S O
N T
EL
EG
RA
PHY
for
an "
up
" of
fice
.In
this
sys
tem
it w
ill b
e se
en th
at a
key
hav
ing
six
term
inal
s, w
hich
is u
sed
as th
e "
incr
emen
t " k
ey, i
s em
ploy
ed u
pon
the
" B
" s
ide,
whi
lst a
thre
e -t
erm
inal
key
,or
dina
rily
use
d up
on th
e "
B "
side
, is
used
upo
n th
e "A
" si
de f
or r
ever
sing
the
dire
ctio
n of
the
curr
ent.
Four
" v
acuu
m "
res
ista
nces
are
incl
uded
in th
e ba
ttery
lead
s co
nnec
ted
with
the
" B
" k
ey.
Whe
n th
e ba
ttery
is a
ccid
enta
lly le
ft s
hort
-cir
cuite
dth
roug
h th
e sp
ring
s of
the
" B
" k
ey th
e "
lam
ps "
glo
w, a
nd a
n au
tom
atic
war
ning
sig
nal i
s th
us g
iven
.In
ano
ther
sys
tem
of
quad
rupl
ex w
orki
ng, k
now
n as
the
" de
crem
ent "
syst
em, t
he "
B "
rel
ay is
wor
ked
by a
dec
reas
e in
the
curr
ent.
The
mag
netic
forc
e du
e to
a c
ompa
rativ
ely
stro
ng "
A "
cur
rent
hol
ds th
e "
B "
rel
ayto
ngue
to s
paci
ng, o
r, in
oth
er w
ords
, aga
inst
the
insu
late
d co
ntac
t stu
d.W
hen
the
" B
" k
ey is
dep
ress
ed th
e cu
rren
t is
wea
kene
d, a
nd th
e fo
rce
actin
g up
on th
e ar
mat
ure
is a
lso
wea
kene
d.T
his
resu
lts in
the
tong
uebe
ing
pulle
d ov
er to
mar
king
by
the
forc
e of
an
anta
goni
stic
spr
ing,
inst
ead
of b
reak
ing
cont
act a
gain
st it
, as
in th
e in
crem
ent q
uadr
uple
x.T
he u
prig
htin
g so
unde
r is
dis
pens
ed w
ith, a
nd th
e re
adin
g so
unde
r is
con
-ne
cted
dir
ect t
o th
e no
n -p
olar
ised
" B
" r
elay
.T
he c
onne
ctio
ns o
f th
etw
o ri
ght-
hand
bac
k te
rmin
als
of th
e "
B "
key
are
rev
erse
d, a
nd a
lso
thos
eof
the
two
left
-han
d te
rmin
als.
FIG
. 79
A s
yste
m o
f w
orki
ng th
e"
B "
sid
e of
incr
emen
tqu
adru
plex
cir
cuits
with
out t
he a
id o
f th
e re
layi
ng s
ound
er h
as r
ecen
tly b
een
intr
oduc
ed.
The
sys
tem
invo
lves
the
use
of c
onde
nser
s fo
r el
imin
atin
g th
e "
kick
s "
or"
chat
teri
ngs
" in
the
soun
der
whe
n a
reve
rsal
of
curr
ent i
s be
ing
effe
cted
at th
e op
posi
te e
nd o
f th
e ci
rcui
t.T
he in
sula
ted
and
cont
act
stop
s of
the
non
-pol
aris
ed r
elay
are
rev
erse
d in
pos
ition
, and
the
loca
l cir
cuit
isjo
ined
up
agai
nst t
he f
orce
of
the
anta
goni
stic
spr
ing.
The
eff
ect o
f th
e"
kick
" in
the
rela
y is
nul
lifie
d by
the
disc
harg
e fr
om a
con
dens
er o
f tw
o
NO
Tts
(A
t TtL
2GB
A.p
ttV.
135
Inic
ro-f
arad
s ca
paci
ty, w
hich
is jo
ined
inpa
ralle
l with
the
soun
der
coils
. The
mom
enta
ry b
reak
in th
e lo
cal c
ircu
it is
thus
cou
nter
acte
d by
the
pass
age
of th
e di
scha
rge
thro
ugh
the
soun
der
coils
.T
he d
isch
arge
sus
tain
s th
em
agne
tisat
ion
of th
e co
res
of th
e so
unde
r an
d pr
even
ts a
dis
rupt
ion
of th
esi
gnal
s. A
con
dens
er o
f ha
lf a
mic
ro -
fara
d ca
paci
ty a
nd a
coi
l of
100
ohm
sre
sist
ance
to ti
me
its d
isch
arge
are
join
ed in
ser
ies,
and
bri
dge
the
air
spac
e be
twee
n th
e re
lay
cont
act t
ongu
e an
d th
e co
ntac
t scr
ew.
The
obje
ct o
f th
is a
rran
gem
ent i
s to
pre
vent
" s
park
ing
" be
twee
n th
e co
ntac
tsc
rew
and
the
cont
act t
ongu
e w
hen
the
loca
l cir
cuit
is b
roke
n.T
hedi
scha
rge
from
this
con
dens
er a
cts
agai
nst t
heel
ectr
o-m
otiv
efo
rce
deve
lope
d by
the
self
-ind
uctio
n in
the
soun
der
coils
, and
the
tend
ency
topr
oduc
e a
spar
k is
con
side
rabl
y re
duce
d.T
he a
rran
gem
ent o
f th
e co
nden
sers
is s
how
n di
agra
mat
ical
ly in
Fig
. 79.
128
NO
TE
S O
N T
EL
EG
RA
PHY
.
CH
APT
ER
XV
II.
TH
E Q
UA
DR
UPL
EX
SY
STE
M.
The
qua
drup
lex
syst
em is
a co
mbi
natio
n of
the
doub
le a
nd s
ingl
ecu
rren
t dup
lex
syst
ems
of w
orki
ng.
By
supe
rim
posi
ng th
e la
tter
upon
the
form
er s
yste
m tw
om
essa
ges
in e
ach
dire
ctio
n m
ay b
e si
mul
tane
ousl
ytr
ansm
itted
ove
r th
e sa
me
line.
Dou
ble
-cur
rent
wor
king
is r
esor
ted
toup
on o
ne s
ectio
n, c
alle
d th
e "
A "
sid
e, w
hile
the
sing
le c
urre
ntsy
stem
is u
sed
upon
the
othe
r se
ctio
n ca
lled
the
" B
" s
ide.
The
rec
eivi
ngin
stru
men
t in
conn
ectio
n w
ith th
e fo
rmer
isan
ord
inar
y po
lari
sed
rela
yw
hich
act
uate
s its
sou
nder
onl
y w
hen
curr
ents
pass
thro
ugh
its c
oils
in a
mar
king
dir
ectio
n, e
xact
ly in
the
man
ner
desc
ribe
d in
con
nect
ion
with
the
doub
le c
urre
nt d
uple
x sy
stem
.U
pon
the
" B
" s
ide
a no
n -p
olar
ised
rel
ay,
whi
ch r
espo
nds
to c
urre
nts
in e
ither
asp
acin
g or
a m
arki
ng d
irec
tion,
is u
sed.
In th
e ca
se o
f th
e "
B "
rel
ay, h
owev
er,
a st
rong
ant
agon
istic
spr
ing
prev
ents
that
inst
rum
ent f
rom
bei
ng a
ctua
ted
exce
pt w
hen
curr
ents
of
rela
tivel
ygr
eat
stre
ngth
pass
thro
ugh
itsco
ils.
Bot
hre
lays
are
diff
eren
tially
wou
nd s
o th
at th
e ou
tgoi
ng c
urre
nts
may
pas
s th
roug
h th
eir
coils
in o
ppos
ite d
irec
tions
, the
inst
rum
ents
bei
ng u
naff
ecte
dw
hen
the
circ
uit i
s ba
lanc
ed f
or q
uadr
uple
x w
orki
ng.
Bri
efly
, the
n, th
e pr
inci
ple
of q
uadr
uple
x w
orki
ng is
bas
edup
on th
e fa
ct th
at tw
o ki
nds
of r
ecei
ving
inst
rum
ents
may
be
empl
oyed
in c
onne
ctio
n w
ith th
esa
me
line-
one
tore
spon
d to
com
para
tivel
y w
eak
curr
ents
flo
win
g in
a c
erta
indi
rect
ion,
and
the
othe
r on
ly to
cur
rent
s of
gre
ater
str
engt
h,ir
resp
ectiv
e of
thei
r di
rect
ion.
The
" A
" k
ey, w
hich
has
onl
y fo
ur te
rmin
als,
is o
f th
eor
dina
ry d
oubl
e cu
r-re
nt p
atte
rn w
ithou
t a s
witc
h, a
nd is
cal
led
the
"re
vers
ing
" ke
y, b
ecau
se it
sac
tion
reve
rses
the
dire
ctio
n of
the
curr
ent.
At t
he d
ista
nt s
tatio
n th
e"
A "
rel
ay is
act
uate
d by
this
curr
ent,
and
reco
rds
a "m
ark
" on
ly w
hen
the
key
is d
epre
ssed
. The
" B
" r
elay
doe
s no
t res
pond
toei
ther
the
mar
king
or th
e sp
acin
g cu
rren
ts s
ent b
y th
e "
A "
key
, as
they
are
not
suff
icie
ntly
stro
ng to
ove
rcom
e th
e fo
rce
of th
e an
tago
nist
ic s
prin
gby
whi
ch th
eto
ngue
of
the
non
-pol
aris
ed "
B "
rel
ay is
hel
d.T
he k
ey u
pon
the
" B
"si
de is
of
the
sing
le c
urre
nt p
atte
rn, a
nd is
cal
led
the
"in
crem
ent "
key
,be
caus
e on
bei
ng d
epre
ssed
it in
crea
ses
the
stre
ngth
of
the c
urre
nt b
y in
clud
-in
g m
ore
cells
in th
e ba
ttery
cir
cuit.
Whe
n th
e "
B "
key
isde
pres
sed
and
the
" A
" k
ey is
at r
est t
he d
ista
nt "
B"
rela
y re
spon
ds b
ecau
se th
e cu
rren
t is
stro
ng e
noug
h to
ove
rcom
e th
e te
nsio
n of
the
anta
goni
stic
spri
ng.
The
" A
" r
elay
is n
ot a
ctua
ted
inco
nseq
uenc
e of
the
curr
ent b
eing
in a
spac
ing
dire
ctio
n.W
hen
both
key
s ar
e de
pres
sed
both
rel
ays
resp
ond,
as
the
curr
ent i
s su
ffic
ient
ly s
tron
g to
act
uate
the
"B"
rela
y an
d is
als
o in
apr
oper
dir
ectio
n to
pro
duce
a m
arki
ng e
ffec
t in
the
" A
" r
elay
.
NO
TE
S O
N T
EL
EG
RA
PHY
.12
9
The
mai
n ba
ttery
is in
two
sect
ions
,on
e be
ing
com
pose
d of
a g
reat
ere
embe
r of
cells
than
the
othe
r.T
he s
mal
ler
sect
ion,
whi
ch h
as a
nel
eare
mot
ive
forc
e of
abo
ut 3
0vo
lts, i
s co
nnec
ted
with
the
key
upon
Lim
" A
" s
ide,
and
a s
paci
ng c
urre
nt o
for
dina
ry s
tren
gth
pass
es to
the
line
film
, tha
t sec
tion
of th
e ba
ttery
whe
n bo
thke
ys a
re a
t res
t.T
he la
rger
Hi.e
tlen,
hav
ing
an e
lect
ro-m
otiv
e fo
rce
of a
bout
70
volts
, is
join
ed to
tile
" A
YH
"
LIN
E
. . .
-111
11I
1111
1111
1111
FIG
. 7 b
."
II"
key,
the
depr
essi
on o
f w
hich
con
nect
s th
ela
rger
sec
tion
of th
ele
ttter
y to
the
smal
ler,
by
way
of
the
uppe
r co
ntac
t spr
ing.
The
cur
rent
hum
the
who
to b
atte
ry p
asse
s th
roug
h th
e co
ntac
t poi
nts
of th
e "
A"
key,
the
dire
ctio
n in
whi
ch th
e cu
rren
t flo
ws
is c
ontr
olle
d by
the
Alle
n of
that
key
.'I'
he ti
pper
elid
low
er c
onta
ct s
prin
gs o
f th
e "
A "
key
are
so
arra
nged
that
bole
ro e
ee la
tet i
s br
oken
at t
he la
tter,
i.e.,
imm
edia
tely
pri
or to
the
138
NO
TE
S O
N T
EL
EG
RA
PHY
.
The
wat
er in
whi
ch th
e ca
ble
is im
mer
sed
shou
ld e
ither
be
conn
ecte
d w
ithth
e po
sitiv
e po
le o
f th
e ba
ttery
or
mak
e a
good
ele
ctri
cal
conn
ectio
n w
ithth
e ea
rth.
The
neg
ativ
e po
leof
the
test
ing
batte
ry is
inva
riab
lyjo
ined
to th
e ca
ble
for
test
ing
purp
oses
, bec
ause
a "
neg
ativ
ecu
rren
t "te
nds
to d
evel
opa
faul
t,w
here
asa
" po
sitiv
e cu
rren
t "is
liabl
eto
tem
pora
rily
vei
l it b
y ox
idis
ing
the
cond
ucto
r.T
he s
tatic
cap
acity
of th
e ca
ble
in th
e ta
nk m
ay b
e as
cert
aine
d by
com
pari
ng th
e di
scha
rge
obta
ined
fro
mit
with
that
fro
ma
stan
dard
cond
ense
r, w
hen
the
cabl
e an
d co
nden
ser
are
char
ged
for
equa
l per
iods
of
time
from
the
sam
e ba
ttery
.T
he c
onde
nser
isfi
rst c
harg
ed a
nd th
endi
scha
rged
thro
ugh
a se
nsiti
ve g
alva
nom
eter
.L
et th
e ca
paci
ty o
f th
e co
nden
ser
beC
and
the
defl
ectio
n pr
oduc
ed b
y th
e di
scha
rge
d.T
he c
able
und
er te
st,
with
its
free
end
insu
late
d, is
then
sub
stitu
ted
for
the
cond
ense
ran
dte
sted
und
er s
imila
r co
nditi
ons.
If th
e ca
paci
ty a
nd d
efle
ctio
n in
this
case
are
rep
rese
nted
by
Ci a
nd d
1 re
spec
tivel
y,th
enC
i: C
::
di:
dC
x d
=
The
" in
sula
tion
" te
st is
mad
e w
ith a
bat
tery
of
abou
t 200
cel
ls o
fei
ther
the
Min
otto
or
Lec
lanc
he ty
pe; a
hig
hly
sens
itive
inst
rum
ent,
such
as th
eD
'Ars
onva
l gal
vano
met
er, b
eing
in c
ircu
it. W
hen
the
cabl
e is
not
of
grea
tle
ngth
this
test
may
be
mad
e by
com
pari
ng th
e in
sula
tion
resi
stan
ce w
itha
stan
dard
meg
ohm
.T
he g
alva
nom
eter
is s
hunt
ed to
obt
ain
a su
itabl
ede
flec
tion
thro
ugh
the
meg
ohm
(R
), w
hich
is e
arth
-co
nnec
ted.
Cal
l thi
sde
flec
tion
d; n
ext t
ake
a re
adin
g d1
, upo
n th
e un
shun
ted
galv
anom
eter
from
the
sam
e ba
ttery
join
ed to
the
cabl
e, th
e la
tter
bein
g di
scon
nect
ed.
The
insu
latio
n re
sist
ance
(R
1), i
n m
egoh
ms,
may
then
be
obta
ined
fro
mth
e fo
llow
ing
form
ula,
whe
re ..
-I-
1 re
pres
ents
the
mul
tiply
ing
pow
erof
the
shun
t.
111
: R :
: d(.
4 +
1)
d1
x d
x+1)
di
d+
1)
orm
egoh
ms.
diB
y m
ultip
lyin
g th
e nu
mbe
r of
meg
ohm
s in
to th
e nu
mbe
r of
kno
ts th
ein
sula
tion
resi
stan
ce p
er k
not i
s ob
tain
ed,
Thi
s re
sist
ance
sho
uld
not b
ele
ss th
an 2
50 m
egoh
ms
per
knot
aft
er th
e ba
ttery
pow
er h
as b
een
appl
ied
for
one
min
ute,
and
it f
requ
ently
rea
ches
1,0
00 m
egoh
ms,
or
1,00
0,00
0,00
0oh
ms
per
knot
.It
is n
eces
sary
to ta
ke th
e re
sist
ance
test
s at
a co
m-
para
tivel
y hi
gh te
mpe
ratu
re, a
bout
754
5.be
caus
e th
e re
sist
ance
-
NO
TE
S O
N T
EL
EG
RA
PHY
.13
9
ofth
edi
-el
ectr
icin
crea
ses
with
a d
ecre
ase
of te
mpe
ratu
re.
Thi
s,it
will
be
obse
rved
, is
the
reve
rse
toth
atof
aco
nduc
tor;
the
insu
latio
n of
a c
able
con
sequ
ently
impr
oves
in th
e co
mpa
rativ
ely
low
tem
pera
ture
at t
he b
otto
m o
f th
e se
a, a
nd th
e co
nduc
tor
resi
stan
ceis
not
like
ly to
incr
ease
.In
cide
ntal
ly it
may
als
o be
men
tione
d th
at th
ere
sist
ance
of
gutta
-per
cha
incr
ease
s w
ith p
ress
ure,
whi
ch a
lso
tend
s to
impr
ove
the
insu
latio
n of
a c
able
aft
er it
is la
id.
The
abo
ve te
sts
are
take
n ea
ch d
ay, a
nd to
rid
the
cabl
e of
any
res
idua
lch
arge
, due
to "
ele
ctri
fica
tion,
" th
e co
nduc
tor
is "
ear
thed
" s
ubse
quen
tto
eac
h te
st.
Ele
ctri
fica
tion
of a
cab
le.
For
the
insu
latio
n te
st a
bat
tery
of
very
hig
hel
ectr
o-m
otiv
e fo
rce
is e
mpl
oyed
and
the
defl
ectio
n of
the
galv
anom
eter
need
le a
t the
out
set i
s co
mpa
rativ
ely
grea
t.T
his
rapi
dly
decr
ease
s du
ring
the
firs
t min
ute
or s
o, h
owev
er, a
s if
the
insu
latio
n of
the
cabl
e im
prov
ed.
The
def
lect
ion
then
dec
reas
es a
t a m
uch
slow
er r
ate
until
fin
ally
it b
ecom
esfa
irly
con
stan
t. T
his
phen
omen
on is
thou
ght t
o be
due
to th
e po
lari
satio
nof
the
di -
elec
tric
of
the
cabl
e.T
he d
ecre
ase
is m
uch
mor
e ra
pid
at a
low
than
a h
igh
tem
pera
ture
, and
an
indi
a-ru
bber
di -
elec
tric
is a
ffec
ted
to a
grea
ter
exte
nt th
an g
utta
-per
cha.
If e
lect
rifi
catio
n pr
ocee
ds r
egul
arly
and
the
cons
eque
ntde
flec
tion
dim
inis
hes
stea
dily
, the
insu
latio
n is
not
cons
ider
ed to
be
impe
rfec
t.T
he p
olar
isat
ion
and
depo
lari
satio
n, in
fac
t,sh
ould
be
effe
cted
reg
ular
ly a
nd in
equ
al p
erio
ds o
f tim
e if
the
cond
ucto
ris
uni
form
ly in
sula
ted.
The
di -
elec
tric
of
a ca
ble
duri
ng it
s el
ectr
ific
atio
n ap
pare
ntly
abs
orbs
a po
rtio
n of
the
char
ge, w
hich
app
ears
to g
radu
ally
soa
k in
to th
e fi
rst
laye
r ne
xt to
the
cond
ucto
r.T
his
laye
r is
qui
ckly
pol
aris
ed o
r el
ectr
ifie
d,th
e ne
xt a
nd s
ubse
quen
t lay
ers
bein
g af
fect
ed m
ore
and
mor
e sl
owly
.
Whe
n a
high
vol
tage
has
bee
n ap
plie
d to
a c
able
a r
esid
ual c
harg
e is
alw
ays
pres
ent a
fter
adi
scha
rge
has
been
obt
aine
d fr
om it
.T
his
cond
ition
is a
nalo
gous
to b
oth
that
of
a L
eyde
n ja
r an
d a
cond
ense
r.If
eith
er b
e le
ft d
isco
nnec
ted
imm
edia
tely
aft
er it
sfi
rst d
isch
arge
and
subs
eque
ntly
join
ed to
a s
ensi
tive
galv
anom
eter
, a d
efle
ctio
n du
e to
the
resi
dual
cha
rge
will
be
obse
rved
.
The
se r
esid
ual c
harg
esap
pear
togr
adua
lly le
akou
tfr
omth
eun
derl
ying
laye
rs o
f th
e di
-el
ectr
ic, a
nd a
per
cept
ible
per
iod
of ti
me
ista
ken
up in
eff
ectin
g a
thor
ough
dis
char
ge.
A te
st f
(Ir
the
insu
latio
nre
sist
ance
of
a ca
ble,
how
ever
, may
be
take
n af
ter
one
min
ute
of e
lect
rifi
ca-
tion;
but
it is
obv
ious
that
if th
e ca
paci
ty te
st w
ere
take
n to
o qu
ickl
yaf
ter
an in
sula
tion
test
the
resi
dual
cha
rges
wou
ld p
rodu
ce e
rror
s.It
isal
way
s sa
fer,
ther
efor
e, to
test
for
cap
acity
fir
st, a
nd it
is e
ssen
tial t
hat
all t
ests
in c
onne
ctio
n w
ith c
able
s sh
ould
be
mad
e w
ith in
stru
men
ts w
ell
insu
late
d.
140
NO
TE
S O
N T
EL
EG
RA
PHY
.
With
the
sam
e re
sist
ance
, the
cap
acity
of
a st
rand
con
duct
or is
gre
ater
than
that
of
a so
lid o
ne, a
s th
e di
amet
er o
f th
efo
rmer
is s
light
ly g
reat
erth
an th
at o
f th
e la
tter.
The
str
and
is p
refe
rabl
e, h
owev
er,
on a
ccou
nt o
fits
gre
ater
fle
xibi
lity.
A c
able
is p
ract
ical
ly a
cyl
indr
ical
con
dens
er, t
heco
nduc
tor
actin
g as
one
plat
e an
d th
e m
etal
she
athi
ng, t
he w
ater
or
the
eart
h, th
eot
her
plat
e.T
he g
utta
-per
cha
has
a co
mpa
rativ
ely
high
spe
cifi
c in
duct
ive
capa
city
,an
d, a
s a
larg
e co
nduc
tor
surf
ace
is e
xpos
ed to
indu
ctio
n, th
e st
atic
capa
city
of
a ca
ble
is v
ery
grea
t.T
here
are
pra
ctic
al li
mits
to th
e si
ze o
fbo
th c
ondu
ctor
and
di -
elec
tric
, the
refo
re th
eca
paci
ty a
nd r
esis
tanc
e ar
ein
vari
ably
hig
h.Fo
r a
give
n di
amet
er o
f th
e co
rean
incr
ease
in th
e si
zeof
the
cond
ucto
r to
red
uce
the
resi
stan
ce w
ould
mea
n an
incr
ease
dca
paci
ty, b
ecau
se th
e pl
ates
wou
ld b
o br
ough
t nea
rer
toge
ther
;w
hile
, on
the
othe
r ha
nd, i
f th
e di
-el
ectr
ic w
ere
incr
ease
d to
redu
ce th
e ca
paci
ty, t
heco
nduc
tor
wou
ld b
e re
duce
d in
dia
met
er a
nd th
ere
sist
ance
acc
ordi
ngly
incr
ease
d.
The
fol
low
ing
law
s go
vern
the
wor
king
spee
d of
cab
les
:-1.
The
rel
ativ
e sp
eed
of tw
o ca
bles
of
the
sam
e le
ngth
var
ies
inve
rsel
yas
the
prod
uct o
f th
eir
resp
ectiv
e ca
paci
ties
and
cond
ucto
rre
sist
ance
s.2.
Cab
les
sim
ilar
in a
ll re
spec
tsex
cept
leng
th h
ave
wor
king
spe
eds
inve
rsel
y pr
opor
tiona
l to
the
squa
res
of th
eir
resp
ectiv
ele
ngth
s.T
he r
ate
of w
orki
ng o
f a
cabl
e de
pend
sup
on th
e tim
e a
curr
ent t
akes
tori
se f
rom
zer
o to
its
max
imum
str
engt
h an
d fa
llag
ain
to z
ero.
Thi
s is
calle
d th
e "
time
cons
tant
," a
nd it
is in
vers
ely
prop
ortio
nal t
o th
e pr
oduc
tof
the
capa
city
and
the
resi
stan
ce o
f th
e ci
rcui
t.W
hen
the
capa
city
(k)
and
the
resi
stan
ce (
r) p
er u
nit l
engt
h(1
) ar
e gi
ven
the
tota
l cap
acity
(K
)is
obt
aine
d by
mul
tiply
ing
k by
1.
The
tota
l res
ista
nce
(R)
issi
mila
rly
foun
d by
mul
tiply
ing
r by
1. H
ence
KR
= k
r12
It w
ill th
eref
ore
he u
nder
stoo
d w
hy th
ew
orki
ng s
peed
var
ies
inve
rsel
yas
the
squa
re o
f th
e le
ngth
of
the
circ
uit.
To
furt
her
incr
ease
the
spee
d of
wor
king
,re
ceiv
ing
inst
rum
ents
of
extr
eme
sens
itive
ness
are
em
ploy
ed, f
or if
the
batte
rypo
wer
wer
e in
crea
sed
the
stat
ic c
harg
e w
ould
be
grea
ter,
ther
efor
e it
wou
ldbe
impr
actic
able
toat
tem
pt m
ore
rapi
dsi
gnal
ling
byth
ism
eans
.O
rdin
ary
rece
ivin
gap
para
tus
lack
s th
e es
sent
ial
sens
itive
ness
;bu
t by
usin
g a
delic
ate
inst
rum
ent s
uch
as T
hom
son'
s m
irro
rga
lvan
omet
er, o
rth
e sy
phon
reco
rder
inve
nted
by
the
sam
e em
inen
t sci
entis
t,hi
ghly
sat
isfa
ctor
yre
sults
are
obt
aine
d.T
hese
inst
rum
ents
, in
addi
tion
tobe
ing
affe
cted
by v
ery
min
ute
curr
ents
, are
act
uate
d w
ithou
t fri
ctio
n,co
nseq
uent
lyth
ere
isa
max
imum
free
dom
ofth
eir
mov
able
part
s.T
he
NO
TE
S O
N T
EL
EG
RA
PHY
.14
1
mir
ror
galv
anom
eter
has
alre
ady
been
desc
ribe
d,so
also
has
the
D'.A
rson
val
galv
anom
eter
whi
chis
the
sam
e ty
peof
inst
ru-
men
t,in
prin
cipl
e,as
the
syph
on r
ecor
der.
In th
e la
st-n
amed
,an
d un
der
the
cont
rol o
f th
e m
ovab
le c
oil,
agl
ass
syph
on is
used
,on
e en
d of
whi
ch d
ips
into
an
ink
-wel
l, w
hile
the
othe
r en
d vi
brat
esho
rizo
ntal
ly a
bove
asl
ip o
fpa
per,
with
out t
ouch
ing
it, a
nd s
purt
sth
e in
k up
on it
s su
rfac
e.Fr
ictio
n be
twee
n th
e sy
phon
and
the
pape
r is
by th
is m
eans
avo
ided
.A
sm
all c
oil i
s su
spen
ded
in a
str
ong
mag
netic
fiel
d be
twee
n th
e po
les
of a
ver
y po
wer
fully
mag
netis
ed h
orse
shoe
-sh
aped
mag
net,
and
in th
e ce
ntre
of
the
coil
a sm
all p
iece
of
soft
iron
isfi
tted.
The
coi
l is
susp
ende
d by
fib
res
of s
ilk, t
here
fore
its
actio
n is
fri
ctio
nles
s.W
hen
the
coil
mov
es e
ither
in th
e on
e di
rect
ion
or th
e ot
her,
acc
ordi
ng to
the
dire
ctio
n of
the
rece
ived
cur
rent
the
syph
on is
act
uate
d an
d re
gist
ers
undu
lato
ry s
igna
ls u
pon
the
pape
r.T
he o
rdin
ary
"das
h" a
nd"
dot "
sys
tem
is n
ot p
ract
icab
le, c
onse
quen
tlyth
e se
ndin
g ap
para
tus
is d
esig
ned
upon
the
sam
e pr
inci
ple
as th
e co
mm
u-ta
tor
of th
e si
ngle
-ne
edle
inst
rum
erl.t
.T
he e
quiv
alen
t of
a da
sh in
this
syst
em ta
kes
no lo
nger
to s
igna
l tha
n a
dot,
whe
reas
a d
ash
in th
eor
dina
ry M
orse
sys
tem
wou
ld p
rodu
ce a
gre
ater
sta
tic c
harg
e in
the
cabl
e.O
no v
ery
impo
rtan
t adv
anta
ge th
e "
mir
ror
" po
sses
ses
is th
at it
s ze
ro is
mov
able
,A
ver
y lo
ng c
able
is n
ot w
holly
dis
char
ged
afte
r ea
ch s
igna
l,bu
t the
rev
ersa
l of
the
batte
ry in
crea
ses,
neu
tral
ises
or
reve
rses
, wha
t may
be c
onsi
dere
d as
a p
erm
anen
t cha
rge
in th
e ci
rcui
t.A
slig
ht v
aria
tion
of th
e ch
arge
aff
ects
the
delic
ate
rece
ivin
g ap
para
tus,
and
a s
igna
l may
be r
ecei
ved
by m
erel
y an
incr
ease
or
a de
crea
se in
the
defl
ectio
n w
ithou
tac
tual
rev
ersa
l bL
g ef
fect
ed.
A d
isad
vant
age
of th
e m
irro
r in
stru
men
tis
that
no
perm
anen
t rec
ord
of th
e si
gnal
s is
mad
e, a
nd a
dar
kene
d ro
oman
d tw
o op
erat
ors
are
esse
ntia
l to
its p
ract
ical
use
.
In o
rder
to e
limin
ate
eart
h cu
rren
ts a
con
dens
er is
inte
rpos
ed b
etw
een
the
rece
ivin
g ap
para
tus
and
the
line.
A. c
ontin
uous
cur
rent
is th
eref
ore
impo
ssib
le, a
nd th
e ap
para
tus
is a
ctua
ted
by c
onde
nser
impu
lses
con
trol
led
by th
e re
vers
ing
mec
hani
sm o
f th
e si
gnal
ling
com
mut
ator
.
For
dupl
ex w
orki
ng th
e "
brid
ge "
sys
tem
is a
dopt
ed, i
n w
hich
the
rece
ivin
g ap
para
tus
is"
brid
ged
" be
twee
n th
e lin
e an
d th
e ar
tific
ial
circ
uit.
The
rec
eivi
ng in
stru
men
t is
actu
ated
by
the
vary
ing
pote
ntia
lspr
oduc
ed a
t its
term
inal
s by
the
sign
allin
g ap
para
tus
at th
e en
ds o
f th
e ci
r-cu
it.T
he "
art
ific
ial "
cir
cuit
for
bala
ncin
g is
now
mad
e up
in o
ne p
iece
of a
ppar
atus
, kno
wn
as a
" g
rid"
con
dens
er, w
hich
com
bine
s re
sist
ance
and
capa
city
and
rep
rese
nts
the
elec
tric
al c
ondi
tions
of
the
line.
The
alte
rnat
e pl
ates
of
tinfo
il ar
e cu
t to
repr
esen
t cer
tain
res
ista
nces
, and
whe
n th
ey a
re jo
ined
in s
erie
s, th
e re
quir
ed c
apac
ity a
nd r
esis
tanc
eto
rep
rese
nt v
ario
us s
ectio
ns o
f th
e ca
ble
are
thus
rea
dily
bro
ught
into
circ
uit,
136
NO
TE
S O
N T
EL
EG
RA
PHY
.
CH
APT
ER
XV
III.
SUB
MA
RIN
E C
AB
LE
S.
The
eff
icie
ncy
of a
sub
mar
ine
cabl
e de
pend
s ch
iefl
yup
on th
e th
ree
follo
win
g co
nditi
ons
:-1.
Its
mec
hani
cal s
tren
gth.
2. T
he d
urab
ility
of
its in
sula
tor
and
prot
ectin
g m
ater
ial.
3. T
he s
peed
of
sign
allin
g.
The
fir
st c
ondi
tion
is m
et to
ave
ry g
reat
ext
ent b
y us
ing
seve
ral w
ires
twis
ted
toge
ther
inst
ead
of a
sol
id c
ondu
ctor
.A
cen
tral
cop
per
wir
e is
surr
ound
ed b
y ot
hers
wou
nd s
pira
lly a
long
its
leng
th.
The
wir
es a
re o
fab
out 9
8 pe
r ce
nt. p
urity
.If
a s
even
-st
rand
con
duct
or is
em
ploy
ed, a
ndea
ch w
ire
has
the
sam
e w
eigh
t for
a g
iven
leng
th, t
he c
entr
alon
e is
exac
tly s
urro
unde
d by
the
rem
aini
ng s
ix.
A c
ondu
ctor
of
this
mak
e is
com
para
tivel
y fl
exib
le, c
onse
quen
tly th
e ri
sk o
f a
tota
l fra
ctur
e is
con
-si
dera
bly
redu
ced.
As
long
as
a fe
w w
ires
rem
ain
inta
ct th
e co
ntin
uity
of th
e ci
rcui
t is
mai
ntai
ned,
and
the
adva
ntag
e is
app
aren
t.T
he in
sula
tion
of th
e co
nduc
tor
is o
f th
e ut
mos
t im
port
ance
, for
the
slig
htes
t und
etec
ted
faul
t in
this
res
pect
wou
ld e
vent
ually
lead
tove
ryse
riou
s co
nseq
uenc
es.
A la
yer
of C
hatte
rton
's c
ompo
und,
whi
ch is
aco
mpo
sitio
n of
gut
ta-p
erch
a, r
esin
and
tar,
is g
iven
to th
e co
nduc
tor
as a
firs
t coa
ting.
The
n fo
llow
s a
laye
r of
gut
ta-p
erch
a, th
e co
mpo
und
and
gutta
-per
cha
bein
g se
rved
alte
rnat
ely,
som
etim
es to
as
man
y as
sev
en o
rei
ght l
ayer
s.A
bra
ss ta
pe is
wou
nd u
pon
the
core
, as
the
cond
ucto
r an
din
sula
ting
mat
eria
l are
term
ed, t
ore
sist
the
atta
cks
ofa
mar
itim
eve
rmif
orm
inse
ct, k
now
n as
the
tere
dos
wor
m,
Thi
s in
sect
bor
es in
to th
eun
prot
ecte
d gu
tta-p
erch
a, a
nd e
vent
ually
des
troy
s it
and
prod
uces
a f
ault.
The
bra
ss ta
pe, h
owev
er, i
s im
perv
ious
to s
uch
atta
cks,
and
the
insu
latio
n is
pres
erve
d.T
he c
able
is th
en s
erve
d w
ith a
coa
ting
of R
ussi
an h
emp
and
fina
lly c
over
ed w
ith s
teel
wir
es.
The
latte
r, w
hich
exa
ctly
sur
roun
d th
eca
ble,
are
wou
nd s
pira
lly a
long
its
leng
th to
act
gen
eral
ly a
s a
prot
ecto
r of
the
vari
ous
cove
ring
s be
neat
h th
em.
The
cab
le is
con
stru
cted
in tw
o -
knot
leng
ths,
and
then
join
ted
to f
orm
any
con
tinuo
us le
ngth
des
ired
.T
he s
ever
al w
ires
of
the
stra
nd a
re f
irst
sol
dere
d in
to a
sol
id m
ass
and
then
sca
rf -
join
ted.
The
join
ts a
re f
requ
ently
wir
ed a
nd r
e -w
ired
, the
end
son
ly o
f th
e la
st la
yer
bein
g so
lder
ed.
In th
e ev
ent o
f a
disc
onne
ctio
n of
the
cond
ucto
r at
the
join
t the
bin
ding
wir
es s
tret
ch o
ut a
nd m
aint
ain
the
cont
inui
ty o
f th
e ci
rcui
t.
The
Pos
t Off
ice
seve
n st
rand
con
duct
or w
eigh
s ab
out 1
07 lb
s.pe
r na
utic
alm
ile, o
r 15
.2 lb
s. p
er k
not f
or e
ach
stra
nd, a
nd it
s in
sula
tor,
or
di -
elec
tric
,
NO
TE
S O
N T
EL
EG
RA
PHY
.13
7
1501
13$.
per
kno
t.T
he p
rote
ctin
g m
ater
ial v
arie
s in
dia
met
er-a
larg
e si
zebe
ing
used
for
the
shor
e en
d, w
here
fri
ctio
n is
like
ly to
be
grea
test
, am
ediu
m s
ize
next
, and
the
ordi
nary
siz
e fo
r th
e de
ep s
ea p
ortio
n.A
fter
abou
t a f
ortn
ight
the
gutta
-per
cha
beco
mes
thor
ough
ly s
et, a
nd th
en th
eca
ble
is la
id in
to a
tank
of
wat
er, w
hich
sho
uld
be h
eate
d to
the
stan
dard
tem
pera
ture
of
75de
g. F
ahr.
Thi
s te
mpe
ratu
re s
houl
d be
mai
ntai
ned
for
a pe
riod
of
24 c
onse
cutiv
e ho
urs
befo
re th
e ca
ble
is te
sted
.A
cro
ss-s
ectio
nof
a f
our
cond
ucto
r ca
ble
is s
how
n in
Fig
. 80.
The
adv
anta
ges
of th
isca
ble
over
the
sing
le c
ondu
ctor
are
that
the
cond
ucto
rsm
ay b
e re
volv
ed
FIG
89
in p
airs
to n
ullif
y th
e ef
fect
s of
indu
ctio
n, a
nd in
cas
e of
a f
ault
aris
ing
a lo
op te
st c
an b
e re
adily
mad
e.
The
fir
st te
st is
for
the
resi
stan
ce o
f th
e co
nduc
tor,
whi
ch s
houl
d no
t be
less
than
11.
18 n
or m
ore
than
11.
65 o
hms
per
knot
at s
tand
ard
tem
pera
-tu
re.
The
nex
t tes
t is
for
the
elec
tro-
stat
ic c
apac
ity o
f th
e ca
ble.
Aba
ttery
of
ten
cells
onl
y is
em
ploy
ed f
or th
is te
st.
A r
efle
ctin
g ga
lvan
o-m
eter
and
a k
ey o
f th
e "
trig
ger
" pa
ttern
are
als
o in
cir
cuit.
With
the
trig
ger
key
in o
pera
tion
the
chan
ge o
f co
nnec
tions
fro
m th
e ba
ttery
circ
uit t
o th
e ga
lvan
omet
er c
ircu
it ca
n be
pro
mpt
ly m
ade.
Dir
ectly
the
trig
ger
is li
fted
the
key
is p
ulle
d aw
ay f
rom
the
batte
ry c
onta
ct p
oint
,an
d it
may
be
eith
er s
harp
ly b
roug
ht o
ver
agai
nst t
he g
alva
nom
eter
cir
cuit
cont
act p
oint
by
the
forc
e of
a s
prin
g or
left
mid
way
bet
wee
n th
e tw
o.
144
NO
TE
S O
N T
EL
EG
RA
PHY
.
on a
pia
no a
nd a
vio
lin a
dif
fere
nce
in th
e to
ne o
f th
e tw
oso
unds
isre
adily
det
ecte
d.T
he n
umbe
r of
vib
ratio
ns is
the
sam
e, a
nd th
e vo
lum
eof
sou
nd e
mitt
ed b
y th
e in
stru
men
tsm
ay b
e eq
ual,
yet t
here
is a
str
ikin
gdi
ffer
ence
in to
ne.
Vib
ratio
ns s
eldo
m h
ave
a st
raig
ht b
ackw
ard
and
forw
ard
mot
ion,
but
are
usu
ally
acc
ompa
nied
by s
light
inte
rmed
iate
puls
atio
ns.
The
inte
rmed
iate
mov
emen
ts a
rere
spon
sibl
e fo
r th
e to
ne o
rqu
ality
of
the
soun
d.
Bef
ore
proc
eedi
ng it
will
als
o be
wel
l,pe
rhap
s, to
rev
iew
our
kno
wle
dge
of m
agne
ts a
nd m
agne
tic s
ubst
ance
s.
A m
agne
t is
surr
ound
ed b
y lin
es o
f fo
rce,
whi
chpe
rvad
e th
e m
agne
ticfi
eld
in v
aryi
ng d
egre
es o
f in
tens
ity.
The
ext
ent o
f th
e m
agne
tic f
ield
isde
term
ined
by
the
lines
of
forc
e an
d ca
n be
dem
onst
rate
dby
sca
tteri
ngir
on f
iling
s in
the
vici
nity
of
the
mag
net.
The
fili
ngs
whi
ch f
all w
ithin
the
mag
netic
fie
ld w
ill a
rran
ge th
emse
lves
alon
g th
e lin
es o
f fo
rces
in th
efo
rm o
f cl
osed
cur
ves.
The
gre
ates
t int
ensi
ty o
f th
e m
agne
tic f
ield
isat
,or
nea
r th
e po
les
of th
e m
agne
t.
Whe
n a
mag
netic
sub
stan
ce is
bro
ught
into
the
mag
netic
fie
ld th
e lin
esof
for
ce a
re d
isto
rted
fro
m th
eir
natu
ral p
ositi
ons,
and
a la
rge
num
ber
ofth
em p
ass
thro
ugh
the
mag
netic
sub
stan
ce.
As
long
ai t
he s
ubst
ance
lies
in th
e m
agne
tic f
ield
the
lines
of
forc
e re
mai
ndi
stor
ted,
but
they
fall
back
to th
eir
norm
al p
ositi
ons
with
its
rem
oval
.If
the
mag
netic
subs
tanc
e be
mad
e to
vib
rate
ther
e w
ill b
e co
rres
pond
ing
redi
stri
butio
ns o
fth
e lin
es o
f fo
rce,
whi
ch w
illva
ry w
ith th
e m
ovem
ents
of
the
vibr
atin
g bo
dy.
Whe
n a
line
of fo
rce
cuts
aco
nduc
tor,
or
whe
n a
cond
ucto
r cu
ts a
line
of
forc
e, a
n el
ectr
o-m
otiv
e fo
rce
is s
et u
p, a
nd, i
f the
con
duct
or fo
rms
part
of a
clo
sed
circ
uit,
acu
rren
t will
flow
thro
ugh
that
circ
uit.
The
str
engt
hof
the
curr
ent g
ener
ated
dep
ends
upon
the
elec
tro-
mot
ive
forc
e de
velo
ped;
the
valu
e of
the
latte
r is
enh
ance
d by
an
incr
ease
in th
ein
tens
ity o
f th
em
agne
tic f
ield
and
the
quic
keni
ng o
f th
e ra
te o
f m
otio
n at
whi
ch th
eco
n.du
ctor
is c
ut.
The
dir
ectio
n of
the
curr
ent i
s de
pend
ent
upon
the
dire
c-tio
n of
the
mot
ion.
If a
coi
l of
wir
e, th
e en
ds o
f ,w
hich
are
conn
ecte
dto
aga
lvan
omet
er,
bew
ound
upon
ape
rman
ent
mag
net
and
mov
ed r
apid
ly f
rom
one
end
toth
eot
her,
itw
ill c
ut th
roug
hth
e m
agne
tic f
ield
, and
the
curr
ent g
ener
ated
will
cau
sea
mom
enta
ryde
flec
tion
of th
e ga
lvan
omet
er n
eedl
e.A
mov
emen
t in
the
oppo
site
dire
ctio
n w
ill p
rodu
ce a
rev
erse
def
lect
ion.
By
fixi
ng a
coi
l upo
n on
epo
le o
f a
mag
net a
nd c
ausi
ng a
mag
netic
sub
stan
ce to
vib
rate
nea
r th
epo
le th
e di
stri
butio
n of
the
lines
of
forc
e w
ill b
e al
tere
d w
ithev
ery
mov
e-m
ent.
With
eve
ry v
aria
tion
of th
e m
agne
tic f
ield
the
lines
of f
orce
will
cut t
hrou
gh th
e co
il.If
, the
n, th
e co
il fo
rms
part
of
a cl
osed
cir
cuit
curr
ents
will
pas
s th
roug
h th
e la
tter
and
corr
espo
nd in
dire
ctio
n an
dst
reng
th w
ith th
e vi
brat
ory
actio
n of
the
mag
netic
sub
stan
ce.
Whe
n th
ela
tter
is a
ppro
achi
ng th
e m
agne
t the
diie
ctio
n of
the
curr
ent w
illbe
suc
h
NO
TE
S O
N T
EL
EG
RA
PHY
.14
5
as to
red
uce
the
attr
activ
e fo
rce
of th
e m
agne
t.A
n op
posi
te e
ffec
t will
be
prod
uced
whe
n th
e m
agne
tic s
ubst
ance
is r
eced
ing
from
the
mag
netic
pol
e.T
he d
irec
tion
of a
cur
rent
cir
cula
ting
in th
e co
il of
an e
lect
ro-m
agne
tde
term
ines
the
pola
rity
dev
elop
ed a
t the
end
s of
the
core
.Si
mila
rly,
if a
coil
of w
ire
be p
lace
dup
on o
ne p
ole
of a
per
man
ent m
agne
t and
a c
urre
ntci
rcul
ated
thro
ugh
it th
e at
trac
tive
forc
e of
the
mag
net w
ill b
e ei
ther
augm
ente
d or
dim
inis
hed
acco
rdin
g to
the
dire
ctio
n of
the
curr
ent.
The
ear
liest
for
m o
f B
ell t
elep
hone
con
sist
s of
a c
ircu
lar
flex
ible
fer
ro-
type
dis
c or
dia
phra
gm, f
irm
ly c
lam
ped
at it
s ed
ge, a
nd f
itted
in f
ront
of
and
at a
bout
one
-hu
ndre
dth
part
of
an in
ch f
rom
the
Nor
th-s
eeki
ngpo
le o
f a
perm
anen
t bar
mag
net.
A s
mal
l coi
l of
insu
late
d co
pper
wir
e,
FIG
. 81.
wou
nd u
pon
a bo
bbin
, is
plac
ed u
pon
the
pole
of
the
mag
net,
and
is c
on-
sequ
ently
in th
e m
ost i
nten
se p
art o
f th
e m
agne
tic f
ield
.T
he w
hole
isen
clos
ed in
an
ebon
ite c
ase,
the
diap
hrag
m b
eing
hel
d in
pos
ition
by
aneb
onite
mou
thpi
ece
scre
wed
on
toth
e ca
sing
ofth
e bo
dy o
f th
ein
stru
men
t.
The
Bel
l tel
epho
ne m
ay b
e us
ed b
oth
as tr
ansm
itter
and
rec
eive
r, a
ndby
com
plet
ing
a ci
rcui
t inc
lytd
ing
two
such
inst
rum
ents
, as
show
n in
Fig.
81,
tele
phon
ic c
omm
unic
abio
n be
com
es p
ract
icab
le.
A la
rge
num
ber
of th
e lin
es o
f fo
rce
abou
t the
mag
net
pass
es th
roug
hth
e ai
r -s
pace
and
dia
phra
gm.
The
latte
r is
con
sequ
ently
attr
acte
d, a
ndth
e ce
ntra
l or
mob
ile p
ortio
n is
dra
wn
tow
ards
the
mag
net.
Whe
n a
soun
d is
pro
duce
d in
the
vici
nity
of
the
diap
hrag
m th
ew
ave
vibr
atio
ns o
f th
e ai
r im
ping
e up
on th
e la
tter,
cau
sing
it to
vib
rate
insy
nchr
onis
m w
ith th
e so
undi
ng b
ody.
Thi
s di
aphr
agm
con
trol
s, b
ym
agne
tic a
nd e
lect
rica
l act
ion,
the
diap
hrag
m o
f th
e ot
her
inst
rum
ent,
whi
ch, i
n vi
brat
ing,
em
its a
sou
nd s
imila
r to
that
whi
ch c
ause
d til
t fir
stdi
aphr
agm
to b
e se
t in
mot
ion.
The
act
ion
of th
e B
ell t
elep
hone
has
bee
n su
mm
edup
as
follo
ws
:-A
sa
Tra
nsm
itter
:1.
Whe
n a
soun
d is
pro
duce
d in
the
vici
nity
of
the
inst
rum
ent t
heso
noro
us v
ibra
tions
of
the
air
due
to th
at s
ound
tran
smit
thei
r en
ergy
to th
edi
aphr
agm
aid
cau
se it
to v
ibra
te in
syn
chro
nism
with
the
soun
ding
bod
y,
146
NO
TE
S O
N T
EL
EG
RA
PHY
.
2. T
he v
ibra
tions
of
the
diap
hrag
m p
rodu
ce r
edis
trib
utio
ns o
f th
e lin
esof
for
ce d
ue to
the
mag
net.
3. T
he li
nes
of f
orce
, whi
le c
hang
ing
from
one
pos
ition
to a
noth
er, c
utth
roug
h th
e co
il an
d se
t up
curr
ents
var
ying
in d
irec
tion
and
stre
ngth
.4.
The
se c
urre
nts
trav
erse
the
line
circ
uit a
nd p
ass
thro
ugh
the
coil
ofth
e re
ceiv
er.
As
a R
ecei
ver
:
1. T
he in
com
ing
curr
ents
var
y th
e at
trac
tive
forc
e of
the
mag
net a
ccor
d-in
g to
thei
r di
rect
ion
and
stre
ngth
.
2. T
he d
iaph
ragm
obe
ys th
ese
chan
ges
of m
agne
tisat
ion,
rec
edin
g fr
omth
e m
agne
t by
its o
wn
elas
ticity
whe
n th
e at
trac
tive
forc
e of
the
mag
net
is r
educ
ed, a
nd a
ppro
achi
ng it
whe
n th
e m
agne
tic s
tren
gth
of th
e m
agne
tis
incr
ease
d.
3. B
y th
is u
ndul
ator
y ac
tion
the
diap
hrag
m v
ibra
tes
in s
ynch
roni
smw
ith th
e di
aphr
agm
of
the
tran
smitt
er.
4. T
he v
ibra
ting
rece
iver
dia
phra
gm p
rodu
ces
sono
rous
vib
ratio
ns o
f th
eai
r an
d em
its a
sou
nd s
imila
r to
that
whi
ch c
ause
d th
e di
aphr
agm
of
the
tran
smitt
er to
vib
rate
.
TR
AN
SMIT
TE
RS.
The
Bel
l tel
epho
ne, a
s a
tran
smitt
er, h
as lo
ng s
ince
giv
enw
ay to
mor
em
oder
n in
stru
men
ts, o
f w
hich
ther
e ar
e th
ree
dist
inct
type
s, v
iz :-
1. C
arbo
n an
d m
etal
tran
smitt
ers.
2. M
icro
phon
es.
3. G
ranu
lar
tran
smitt
ers.
With
the
Bel
l ins
trum
ent,
the
tran
sfor
mat
ion
of w
ave
vibr
atio
ns o
f th
e ai
rto
ele
ctri
cal w
aves
is th
e re
sult
of e
lect
ro-m
agne
tic in
duct
ion,
but
with
eac
hof
the
abov
e -m
entio
ned
form
s of
tran
smitt
ers
the
curr
ents
are
obt
aine
dfr
om a
bat
tery
.T
he s
onor
ous
vibr
atio
ns o
f th
e ai
r im
ping
e up
on th
edi
aphr
agm
s an
d ca
use
the
elec
tric
al r
esis
tanc
e of
the
tran
smitt
ers
to b
eva
ried
.T
he b
atte
ry is
con
nect
ed w
ith th
e tr
ansm
itter
in e
ach
case
, and
the
curr
ents
flu
ctua
te in
str
engt
h w
ith th
e va
ryin
g re
sist
ance
in a
ccor
d-an
ce w
ith O
hm's
law
.
The
fir
st in
stru
men
t of
the
carb
on a
nd m
etal
type
was
inve
nted
by
Edi
son.
It w
as f
ollo
wed
by
Bla
ke's
tran
smitt
er, a
nd a
s th
e la
tter
is th
ebe
st k
now
n of
its
clas
s, a
bri
ef d
escr
iptio
n of
this
inst
rum
ent i
s he
re g
iven
.
The
Bla
ke T
rans
mitt
er.-
Imm
edia
tely
beh
ind
the
mou
thpi
ece
M(F
ig. 8
2), w
hich
is c
arri
ed b
y th
e ca
se o
f th
e in
stru
men
t, a
ring
of
iron
isfi
xed,
and
to it
are
fitt
ed ir
on p
roje
ctio
ns A
Al,
one
at th
e to
p an
d th
eot
her
at th
e bo
ttom
.T
he d
iaph
ragm
JD
is a
mob
ile f
erro
type
dis
c, w
hich
NO
TE
S O
N T
EtE
GR
API
V.
147
is f
itted
into
a r
ubbe
r ri
ng, t
he w
hole
bei
ng h
eld
in p
ositi
on b
y m
eans
ofst
eel s
prin
gs a
ttach
edto
the
iron
rin
g.T
o th
e up
per
proj
ectio
nis
secu
red
a fl
exib
le b
rass
spri
ng, w
hich
car
ries
an
angl
e -p
iece
K,
the
low
erpo
rtio
nof
whi
chab
uts
agai
nst
anad
just
able
scre
wS
carr
ied
byth
elo
wer
proj
ectio
n.A
tth
eup
per
end
of
FIG
82.
the
angl
e -p
iece
are
two
stee
l spr
ings
,in
sula
ted
one
from
the
othe
r.T
he s
prin
g ne
xt to
the
diap
hrag
m h
as it
s fr
ee e
nd f
itted
with
a p
latin
umco
ntac
t poi
nt.
The
oth
er s
prin
g te
rmin
ates
in a
cir
cula
r br
asa
plat
eca
rryi
ng a
sm
all c
arbo
n di
sc.
latte
r pr
esse
s up
on th
e pl
atin
um e
onta
ct a
nd h
olds
it a
gain
st th
e ce
ntre
of
the
diap
hrag
m.
The
se s
prin
gs a
rojo
ined
to th
e te
rmin
als
of th
e in
stru
men
t and
the
curr
ent p
asse
s th
rotm
l,th
em a
nd th
e ca
rbon
-pl
atin
um ju
nctio
n.T
he in
stru
men
t is
adju
sted
I'y
mea
ns o
f th
e sc
rew
at t
he lo
wer
pro
ject
ion,
the
pres
sure
exi
stin
g bo
twr,
,,,,
the
diap
hrag
m, p
latin
um c
onta
ct a
nd c
arbo
n di
sc b
eing
var
ied
at w
ill.
'I'1,
,,
vibr
atio
n of
the
diap
hrag
m, c
ause
d by
sou
nd w
aves
impi
ngin
g up
on I
t, pi
..du
ces
a gr
eate
r or
less
er in
timac
y of
con
tact
bet
wee
n th
e pl
atin
um v
omit
and
carb
on d
isc,
and
the
elec
tric
al r
esis
tanc
e be
twee
n th
em I
I 'in
tim to
s w
Il li
the
natu
re o
f th
e vi
brat
ions
impa
rted
to th
e di
aphr
agm
.T
ho m
irth
& I
nco
nseq
uent
ly o
f a
vary
ing
char
acte
r an
d th
e re
ceiv
ing
appa
rato
o In
aoL
ugth
olac
cord
ingl
y.
The
Mic
roph
one.
-The
mic
roph
one
is a
n in
stru
men
t the
ono
of
vohl
i.hde
pend
s up
on a
sys
tem
of
loos
e co
ntac
ts, a
nd w
as in
vent
ed b
y Pr
eibm
i...
148
NO
TE
S O
N T
EL
EG
RA
PHY
.
Hug
hes
in 1
878.
Man
y ex
peri
men
ts h
ave
been
mad
e to
det
erm
ine
the
best
sub
stan
ce to
be
empl
oyed
, but
the
mer
its o
f ca
rbon
hav
e re
nder
ed it
sus
e ex
clus
ive.
The
inst
rum
ent
may
be
cons
ider
ed a
s a
who
lly c
arbo
ntr
ansm
itter
, and
the
arra
ngem
ent o
f th
e lo
ose
cont
acts
may
be
vari
ed in
man
y w
ays.
One
of
the
earl
iest
for
ms
ofm
icro
phon
es c
onsi
sted
of
asi
ngle
car
bon
penc
il ar
rang
ed lo
osel
y be
twee
ntw
o fi
xed
carb
on b
lock
s.E
xper
ienc
e so
on s
how
ed, h
owev
er, t
hat b
ette
rre
sults
wer
e ob
tain
edby
usin
g m
ore
than
one
pen
cil,
and
in a
ll th
e la
ter
form
s of
mic
roph
one
the
batte
ry c
urre
nt p
asse
s th
roug
h a
num
ber
ofpe
ncils
arr
ange
d in
par
alle
l.C
arbo
n is
inox
idis
able
and
infu
sibl
e, a
nd th
e he
at e
ffec
tspr
oduc
ed b
yth
e pa
ssag
e of
a c
urre
ntth
roug
h it
enha
nce
its v
alue
in c
onne
ctio
nw
ithtr
ansm
itter
s.
Thr
ee a
ccep
ted
fact
s m
ust b
e he
re s
tate
din
ord
er th
at th
e he
at e
ffec
tsm
ay b
e un
ders
tood
.1.
Tha
t an
elec
tric
cur
rent
pass
ing
thro
ugh
any
cond
ucto
r ra
ises
the
tem
pera
ture
of
that
con
duct
or.
2. T
hat t
he a
mou
nt o
f he
at is
grea
test
at t
he p
oint
of
grea
test
resi
stan
ce,
albe
it th
e st
reng
th o
f th
e cu
rren
t is
unif
orm
in th
e w
hole
cir
cuit.
3. T
hat c
arbo
npo
sses
ses
the
pecu
liar
prop
erty
ofin
crea
sing
inre
sist
ance
whe
n its
tem
pera
ture
islo
wer
ed.
Mos
t met
als,
of
cour
se, a
reop
posi
tely
aff
ecte
d.
The
theo
ry o
f th
e m
icro
phon
em
ay b
e st
ated
thus
: T
he m
echa
nica
lvi
brat
ions
of
the
penc
ils c
ause
the
resi
stan
ce a
t the
poin
ts o
f lo
ose
cont
act t
o be
var
ied.
An
incr
ease
d re
sist
ance
caus
es th
e cu
rren
t to
bere
duce
d in
str
engt
h.T
he te
mpe
ratu
re a
t the
poin
ts o
f co
ntac
t, th
eref
ore,
falls
, and
the
resi
stan
ce is
fur
ther
incr
ease
d.W
ith a
dec
reas
e of
res
ist-
ance
, cau
sed
by a
n in
crea
sed
pres
sure
at t
he p
oint
s of
con
tact
bet
wee
nth
epe
ncils
and
car
bon
bloc
ks, t
he c
urre
nt is
augm
ente
d an
d th
e te
mpe
ratu
rein
crea
sed.
The
hea
t eff
ect p
rodu
ces
a fu
rthe
r re
duct
ion
in th
ere
sist
ance
,an
d it
will
, the
refo
re, b
ese
en th
at a
gre
ater
var
iatio
n in
the
curr
ent i
sen
sure
d by
the
mec
hani
cal v
ibra
tions
of c
arbo
n pe
ncils
than
wou
ld b
eth
e ca
se if
any
oth
er s
ubst
ance
wer
e us
ed.
The
Gow
er -
Bel
l Tra
nsm
itter
.-T
his
inst
rum
ent
isth
e be
st-k
now
ntr
ansm
itter
of
the
mic
roph
one
clas
s.T
he d
iaph
ragm
isa
deal
boa
rd,
bene
ath
whi
ch a
re e
ight
car
bon
penc
ils a
rran
ged
in s
ets
of f
our.
Atta
ched
to th
e di
aphr
agm
are
two
thin
V-s
hape
d st
rips
of
copp
er, u
pon
each
of
whi
ch a
re f
itted
fou
r ci
rcul
arca
rbon
blo
cks.
Mid
way
bet
wee
n th
eco
pper
stri
ps a
som
ewha
t lar
ger
carb
on b
lock
isfi
xed,
and
bet
wee
n it
and
the
eigh
t blo
cks
are
eigh
t car
bon
penc
ils, s
o ar
rang
ed th
aton
e en
d of
eac
hre
sts
loos
ely
in a
n op
enin
g in
the
cent
ral
bloc
k.T
he o
ther
ext
rem
ities
of
the
penc
ils a
re s
uppo
rted
by th
e ei
ght s
urro
undi
ng b
lock
s.(F
ig. 8
3.)
The
cop
per
stri
ps v
irtu
ally
for
mth
e te
rmin
als
of th
ein
stru
men
t.T
he
NO
TE
S O
N T
EL
EG
RA
PHY
.14
9
curr
ent d
ivid
es th
roug
h on
e se
t of
four
pen
cils
, pas
ses
thro
ugh
the
cent
ral
bloc
k, a
nd a
gain
div
ides
thro
ugh
the
seco
nd s
et o
f pe
ncils
, lea
ving
the
inst
rum
ent b
y w
ay o
f th
e co
pper
str
ip.
The
dia
phra
gm r
ests
upo
n in
dia-
rubb
er w
ashe
rs, w
hich
tend
to d
amp
out v
ibra
tions
con
tinue
d af
ter
the
soun
d w
aves
hav
e ce
ased
to in
flue
nce
the
diap
hrag
m.
The
latte
r is
usua
lly c
over
ed b
y a
woo
den
casi
ng, a
t the
cen
tre
of w
hich
a p
orce
lain
mou
thpi
ece
is a
ttach
ed to
dir
ect t
he s
ound
wav
es to
the
diap
hrag
m, w
hich
is f
ixed
in a
slo
ping
pos
ition
.
The
sou
nd w
aves
impi
nge
upon
the
diap
hrag
m a
nd c
ause
it to
vib
rate
,an
d by
the
mov
emen
ts s
o pr
oduc
ed th
e el
ectr
ical
res
ista
nce
of th
e lo
ose
cont
acts
is v
arie
d.W
hen
the
diap
hrag
m p
erfo
rms
a do
wnw
ard
mot
ion,
carr
ying
the
carb
on b
lock
s w
ith it
, the
pen
cils
do
not i
mm
edia
tely
fol
low
thei
r su
ppor
ting
bloc
ks, a
nd th
e am
ount
of
cont
act i
s th
ereb
y re
duce
d.W
hen
an u
pwar
d m
ovem
ent i
s ex
ecut
ed th
e pe
ncils
are
rai
sed
by th
eir
supp
orts
aga
inst
the
forc
e of
gra
vity
, and
, in
cons
eque
nce
of th
e in
crea
sed
pres
sure
, a d
imin
utio
n of
the
resi
stan
ce a
t the
poi
nts
of c
onta
ct r
esul
ts.
FIG
. 83.
Prof
esso
r H
ughe
s at
trib
uted
the
vary
ing
resi
stan
ce to
the
fact
that
the
amou
nt o
f co
ntac
t, or
the
num
ber
of m
olec
ules
of
carb
on a
t the
poi
ntof
con
tact
taki
ng p
art i
n th
e tr
ansm
issi
on o
f th
e cu
rren
t, va
ried
with
the
chan
ges
of p
ositi
on o
f th
e pe
ncils
, due
ta th
e vi
brat
ion
of th
e di
aphr
agm
.T
his,
how
ever
, can
per
haps
be
sum
med
q in
the
wor
ds o
f D
u M
once
l-th
at a
n in
crea
se o
f pr
essu
re b
etw
een
two
cond
ucto
rs in
con
tact
pro
duce
s a
dim
inut
ion
of th
eir
elec
tric
al r
esis
tanc
es.
Gra
nula
r T
rans
mitt
ers.
-In
orde
r th
atth
iscl
ass
oftr
ansm
itter
may
be
prop
erly
und
erst
ood
it w
ill b
e w
ell
to f
ollo
w u
p th
e m
any
impr
ovem
ents
whi
ch h
ave
been
mad
e up
on th
e fi
rst o
f th
e gr
anul
ar ty
pe,
know
n as
the
Hun
ning
's tr
ansm
itter
.In
this
inst
rum
ent t
wo
plat
inum
disc
s, o
ne o
f w
hich
ser
ves
as th
e di
aphr
agm
, are
sep
arat
ed b
y a
spac
e of
abou
t one
-ei
ghth
of
an in
ch, w
hich
is f
illed
with
car
bon
gran
ules
.T
hefr
ont d
isc,
A, F
ig. 8
4, is
hel
d in
pos
ition
by
a m
etal
rin
g R
, and
the
who
le is
enc
lose
d in
a w
oode
n ca
se, t
he f
ront
por
tion
of w
hich
car
ries
am
outh
piec
e M
and
cla
mps
the
diap
hrag
m a
nd r
ing
in p
ositi
on.
A f
ine
150
NO
TE
S O
N T
EL
EG
RA
PHY
.
wir
e ga
uze
is f
itted
bet
wee
n th
em
outh
piec
e an
d di
aphr
agm
and
ser
ves
to p
rote
ct th
e la
tter
from
moi
stur
ean
d da
mag
e.T
he b
ack
plat
inum
plat
e B
is c
onne
cted
with
one
term
inal
of
the
inst
rum
ent,
whi
le th
ese
cond
term
inal
is jo
ined
to th
edi
aphr
agm
.W
hen
the
latte
r is
cau
sed
to v
ibra
te b
y so
und
wav
esim
ping
ing
upon
it, t
he r
esis
tanc
e be
twee
n th
epl
atin
um p
late
s va
ries
in a
ccor
danc
e w
ith th
efl
uctu
atin
g pr
essu
re e
xert
edup
on th
e gr
anul
es, a
nd th
e st
reng
th o
f th
e cu
rren
tri
ses
and
falls
inin
vers
e ra
tio to
the
tota
l res
ista
nce
of th
e ci
rcui
t.T
he g
reat
dra
wba
ckto
this
inst
rum
ent i
s th
at, a
fter
a tim
e, th
e gr
anul
es s
ettle
dow
n, a
ndth
ose
at th
e bo
ttom
bec
ome
firm
ly w
edge
d to
geth
er,
The
latte
r th
en
FIG
. 84.
form
a s
hort
-cir
cuit
acro
ss th
eop
erat
ive
gran
ules
at t
he c
entr
e of
the
inst
rum
ent,
whe
re th
e am
plitu
de o
f vi
brat
ion
isgr
eate
st.
The
eff
ect u
pon
the
vary
ing
resi
stan
ce o
f th
e tr
ansm
itter
may
be
grap
hica
lly d
emon
stra
ted
by a
pplic
atio
ns o
f th
e la
w o
f jo
int r
esis
tanc
es.
Supp
ose
that
the
tran
s-m
itter
has
a n
orm
al r
esis
tanc
eof
8 oh
ms,
and
that
with
a c
erta
invi
brat
ion
the
resi
stan
ce is
var
ied
betw
een
6 an
d 10
ohm
s.T
he c
urre
ntw
ill f
luct
uate
with
the
chan
ging
res
ista
nce.
Imag
ine,
how
ever
, wha
tw
ould
be
the
effe
ct if
the
gran
ules
at t
hebo
ttom
of
the
inst
rum
ent
shou
ld b
ecom
e so
pac
ked
as to
off
era
resi
stan
ce b
etw
een
the
two
plat
inum
plat
es o
f on
ly 4
ohm
s.T
he o
pera
tive
gran
ules
at t
he c
entr
ew
ould
be
prac
tical
ly s
hort
-cir
cuite
d, a
nd th
e vi
brat
ion
inst
ead
ofpr
oduc
ing
ava
riat
ion
of 4
ohm
s w
ould
res
ult i
na
vari
atio
n ra
ngin
g be
twee
n th
ejo
int r
esis
tanc
e of
4 o
hms
and
6 oh
ms
and
that
of
4 oh
ms
and
10 o
hms.
The
for
mer
res
ista
nce
is 2
:4 o
hms
and
the
latte
r29
ohm
s, th
e di
ffer
ence
betw
een
them
bei
ng le
ss th
an h
alf
an o
hm.
The
flu
ctua
tion
of th
ecu
rren
t wou
ld c
onse
quen
tly b
eve
ry li
ttle,
and
the
rece
iver
wou
ld b
e bu
tfe
ebly
act
uate
d, w
here
as in
the
abse
nce
of th
e pa
ckin
g of
the
gran
ules
good
res
ult w
ould
be
obta
ined
with
the
vari
atio
n in
the
resi
stan
ce o
f th
ein
stru
men
t bet
wee
n 6
and
10 o
hms.
NO
TE
S O
N T
EL
EG
RA
PHY
.15
1
Thi
s "
pack
ing
diff
icul
ty "
was
a s
erio
us d
raw
back
to th
e H
unni
ng's
tran
smitt
er, a
nd m
any
mod
ific
atio
ns o
f th
e in
stru
men
t hav
e be
en d
evis
edw
ith a
vie
w to
its
elim
inat
ion.
In th
e M
osel
ey tr
ansm
itter
the
plat
inum
diap
hrag
m w
as r
epla
ced
by a
thin
pin
e bo
ard,
to th
e ce
ntre
of
whi
ch a
smal
l dis
c of
car
bon
was
atta
ched
. The
latte
r ac
ted
as th
e fr
ont e
lect
rode
,an
d th
e sp
ace
betw
een
it an
d th
e ba
ck e
lect
rode
was
mad
e w
edge
-sha
ped
by in
clin
ing
the
diap
hrag
m a
nd th
e ba
ck p
late
toge
ther
, the
ang
le f
orm
edbe
ing
at th
e bo
ttom
of
the
inst
rum
ent.
By
this
arr
ange
men
t the
con
tact
betw
een
the
gran
ules
and
the
back
ele
ctro
de w
as m
ore
unif
orm
, but
the
" pa
ckin
g "
was
not
alto
geth
er e
limin
ated
.T
he g
ranu
les
whi
ch h
adbe
com
e w
edge
d to
geth
er, h
owev
er, f
orm
ed n
o pa
rt o
f th
e ci
rcui
t, as
they
wer
e no
t in
cont
act w
ith th
e ca
rbon
dis
c.T
hey
wer
e th
us r
ende
red
inop
erat
ive
and
a gr
eate
r ef
fici
ency
was
pro
duce
d.
The
Hun
ning
's-c
one
or D
ecke
rt tr
ansm
itter
is a
noth
er in
stru
men
t of
the
gran
ular
type
.It
is in
ext
ensi
ve u
se b
y th
e Po
st O
ffic
e an
d gi
ves
gene
ral s
atis
fact
ion.
The
dia
phra
gm a
nd b
ack
elec
trod
e ar
e bo
th c
arbo
n,th
e fo
rmer
bei
ng a
thin
dis
c an
d th
e ot
her
a ci
rcul
ar b
lock
, the
fro
nt o
fth
e la
tter
bein
g ca
rved
into
the
shap
e of
pyr
amid
s. T
he a
rran
gem
ent o
f th
epy
ram
ids
or c
ones
is s
how
n in
Fig
. 85.
Im
med
iate
ly b
ehin
d th
e di
aphr
agm
is a
woo
llen
ring
whi
ch a
llow
s on
ly th
e gr
anul
es a
t the
cen
tre
of th
ein
stru
men
t to
be in
con
tact
with
the
diap
hrag
m.
The
woo
llen
ring
ser
ves
FIG
85
the
purp
ose
of c
uttin
g ou
t of
the
circ
uit t
he g
ranu
les
whi
ch, p
erch
ance
,ha
ve b
ecom
e pa
cked
at t
he b
otto
m o
f th
e tr
ansm
itter
.T
he o
bjec
t of
the
carv
ed b
ack
elec
trod
e is
to p
rom
ote
grea
ter
unif
orm
ity o
f co
ntac
t with
the
gran
ules
and
, in
orde
r to
ens
ure
a pr
oper
dis
trib
utio
n of
the
latte
r, th
eap
ex o
f on
e py
ram
id is
situ
ated
imm
edia
tely
opp
osite
the
groo
ve f
orm
edby
the
two
adja
cent
pyr
amid
s in
the
next
row
.(F
ig. 8
5.)
The
pyr
amid
sfa
cing
the
cent
re o
f th
e di
aphr
agm
, i.e
., th
e po
rtio
n no
t shi
elde
d by
the
woo
llen.
rin
g, a
re s
light
ly f
latte
ned
or tr
nnea
ted,
and
to th
em a
re g
umm
ed
152
NO
TE
S O
N T
EL
EG
RA
PHY
.
smal
l tuf
ts o
f si
lk.
The
latte
r br
idge
the
spac
e be
twee
n th
e el
ectr
odes
and
tend
:;o d
amp
out v
ibra
tions
not
sus
tain
edby
con
tinue
d so
und
wav
esim
ping
ing
upon
the
diap
hrag
m.
The
inst
rum
ent k
now
n as
the
"sol
id -
back
"T
rans
mitt
er is
an
Am
eric
anpr
oduc
tion
and
is v
ery
effe
ctiv
e fo
r lo
ng d
ista
nce
tele
phon
y.T
he tw
oca
rbon
ele
ctro
des
are
arra
nged
in a
sm
all c
ham
ber
fille
d w
ith c
arbo
ngr
anul
es.
The
cha
mbe
r is
lined
with
an
insu
latin
g m
ater
ial
and
issl
ight
ly la
rger
in d
iam
eter
than
the
carb
on d
iscs
.B
y th
is a
rran
gem
ent
the
gran
ules
at t
he b
otto
m o
f th
e ce
llar
o no
t in
the
path
of
the
curr
ent,
and
cons
eque
ntly
the
pack
ing
diff
icul
ty is
prac
tical
ly o
verc
ome.
The
fro
ntel
ectr
ode
is a
ttach
ed to
a f
erro
type
dia
phra
gmby
mea
ns o
f a
smal
l scr
ewan
d w
ashe
r, w
hile
the
seco
nd c
arbo
n di
sc is
arra
nged
at t
he b
ack
of th
eco
ntai
ning
cel
l and
is c
apab
le o
f ad
just
men
t by
mea
ns o
fa
scre
w.
The
two
disc
s ar
o co
nnec
ted
to th
e te
rmin
als,
and
the
inst
rum
ent,
whi
ch is
ave
ry e
ffic
ient
tran
smitt
er, i
s pr
actic
ally
fre
e fr
om th
e pa
ckin
g tr
oubl
e.
TH
E I
ND
UC
TIO
N C
OIL
.
The
fun
ctio
n of
the
tran
smitt
er in
ate
leph
one
circ
uit i
s to
pro
duce
ava
riat
ion
in th
e el
ectr
ical
res
ista
nce
of th
e ci
rcui
tby
mea
ns o
f so
und
wav
es im
ping
ing
upon
the
diap
hrag
m.
The
rec
eive
r re
spon
ds n
ot to
the
actu
al s
tren
gth
of th
e cu
rren
t pas
sing
thro
ugh
itsco
ils, b
ut to
the
vari
atio
n in
the
stre
ngth
of
the
curr
ent.
It w
ill, t
here
fore
, bo
seen
that
in o
rder
to o
btai
n as
gre
at a
n ef
fect
as
poss
ible
, the
var
ying
res
ista
nce
ofth
e tr
ansm
itter
mus
t pro
duce
a m
axim
um f
luct
uatio
nin
the
stre
ngth
of
the
curr
ent.
Thi
s ca
n on
ly b
e do
ne b
y ke
epin
g th
ere
sist
ance
of
the
batte
ry c
ircu
it as
low
as
poss
ible
, so
that
the
slig
htes
t cha
nge
in th
ere
sist
ance
of
the
tran
smitt
er w
ill p
rodu
ce a
nap
prec
iabl
e ef
fect
upo
n th
ecu
rren
t.Fo
r in
stan
ce, s
uppo
se th
at a
cer
tain
sou
ndw
ave
caus
es th
etr
ansm
itter
to in
crea
se in
res
ista
nce
by 1
ohm
, and
that
the
inst
rum
ent
form
s pa
rt o
f a
circ
uit o
f 50
0 oh
ms
resi
stan
ce.
The
add
ition
al 1
ohm
will
cau
se th
e st
reng
th o
f th
e cu
rren
t to
be a
ltere
dve
ry s
light
ly, f
orth
e re
sist
ance
of
the
who
le c
ircu
it w
ill b
e al
tere
don
ly f
rom
500
to 5
01oh
ms,
and
the
curr
ent w
ill v
ary
by a
bout
one
fiv
e -h
undr
edth
part
of
itsfo
rmer
val
ue.
But
if th
e tr
ansm
itter
had
for
med
part
of
a ci
rcui
t of
5oh
ms
resi
stan
ce, w
hich
was
incr
ease
d to
6 o
hms
by th
e ac
tion
of th
edi
aphr
agm
, the
cur
rent
wou
ld h
ave
been
dec
reas
ed b
yon
e -s
ixth
of
itsst
reng
th.
It w
ill, t
here
fore
, be
appa
rent
that
in o
rder
to o
btai
n a
max
imum
var
iatio
n of
cur
rent
the
resi
stan
ce o
f th
etr
ansm
itter
cir
cuit
shou
ld b
e as
low
as
poss
ible
, and
to b
ring
abo
ut th
isre
sult
an in
duct
ion
coil
is in
trod
uced
.T
he b
atte
ry e
mpl
oyed
for
spe
akin
gpu
rpos
es is
usu
ally
of th
e A
gglo
mer
ate
Lec
lanc
he ty
pe, w
hich
has
a re
sist
ance
of
abou
tha
lf a
n oh
m p
er c
ell.
Tw
o su
ch c
ells
are
suf
fici
ent f
or th
epu
rpos
e.A
n in
duct
ion
coil
cons
ists
ess
entia
lly o
f tw
o co
ils o
fin
sula
ted
wir
ew
ound
one
upo
n th
e ot
her
arou
nd a
sof
t iro
nco
re.
The
latte
r is
not
NO
TE
S O
N T
EL
EG
RA
PRY
.15
8
an o
rdin
ary
bar
oir
on, b
ut is
com
pose
d of
a b
undl
e of
ver
y so
ft ir
onw
ires
.A
cor
e of
this
des
crip
tion
faci
litat
es m
agne
tisat
ion
and
dem
ag-
netis
atio
n.T
he p
rim
ary
coil,
or
the
coil
wou
nd im
med
iate
ly u
pon
the
core
, is
com
pose
d of
fai
rly
thic
k w
ire
and
is c
ompa
rativ
ely
shor
t.It
sre
sist
ance
is, t
here
fore
, ver
y lo
w.
The
sec
onda
ry c
oil i
s w
ound
upon
the
prim
ary
coil,
and
as
its r
esis
tanc
eis
not
of
seri
ous
mom
ent,
it is
pos
sibl
e an
d ad
vant
ageo
us to
em
ploy
a c
on.
duct
or o
f sm
alle
r ga
uge
and
grea
ter
leng
th.
The
tran
smitt
er a
nd b
atte
ryar
e co
nnec
ted
to th
e pr
imar
y co
il, a
nd a
clo
sed
circ
uit i
s th
us f
orm
ed. T
hese
cond
ary
coil
is c
onne
cted
with
the
line.
Whe
n so
und
wav
es im
ping
eup
on th
e di
aphr
agm
of
the
tran
smitt
er th
e re
sist
ance
of
the
inst
rum
ent
vari
es in
acc
orda
nce
with
the
natu
re o
f th
em, a
nd th
e cu
rren
t bec
omes
undu
lato
ry.
In c
onse
quen
ce o
f th
e ex
ceed
ingl
y lo
w r
esis
tanc
e of
the
circ
uit t
he c
urre
nt is
com
para
tivel
y st
rong
, and
a s
tron
g m
agne
tic f
ield
isde
velo
ped
in th
e pr
imar
yco
il.T
he c
urre
nt, h
owev
er,
bein
gof
afl
uctu
atin
g ch
arac
ter,
cau
ses
a re
dist
ribu
tion
of th
e lin
es o
f fo
rce
with
ever
y va
riat
ion,
and
the
actio
n up
on th
e se
cond
ary
coil
(see
Cha
p. X
II.)
is to
indu
ce a
n un
dula
tory
ele
ctro
-mot
ive
forc
e w
hich
ris
es a
nd f
alls
with
the
curr
ent i
n th
e pr
imar
y ci
rcui
t.T
he e
lect
ro-m
otiv
e fo
rce
deve
lope
dde
pend
s up
on th
e in
tens
ity o
f th
e m
agne
tic f
ield
and
als
o up
on th
e su
rfac
eex
pose
d to
indu
ctio
n.T
he s
tren
gth
of th
e cu
rren
t pas
sing
thro
ugh
the
prim
ary
coil
dete
rmin
es th
e fo
rmer
and
the
num
ber
of tu
rns
of w
ire
inth
e se
cond
ary
coil
the
latte
r.In
ord
er, t
here
fore
, to
ensu
re th
e ou
ter
conv
olut
ions
of
the
seco
ndar
y co
il be
ing
wel
l wst
hin
the
mag
netic
fie
ld a
wir
e of
sm
all g
auge
isem
ploy
ed.
The
line
isco
nnec
ted
with
the
seco
ndar
y co
il, a
nd c
urre
nts
flow
thro
ugh
it w
hich
var
y in
dir
ect r
atio
toth
e el
ectr
o-m
otiv
e fo
rce
gene
rate
d.Fi
g. 8
6 in
dica
tes
the
theo
retic
al c
on-
nect
ions
of
the
indu
ctio
n co
il.
The
fol
low
ing
figu
res
indi
cate
the
rela
tive
dim
ensi
ons
of th
e co
ils, a
ndan
indu
ctio
n co
il of
this
con
stru
ctio
n se
rves
its
purp
ose
adm
irab
ly :
Prim
ary
Coi
l. -1
06 c
onvo
lutio
ns, t
he w
ire
havi
ng a
dia
met
er o
f 20
mils
and
the
exce
edin
gly
kw to
tal r
esis
tanc
e of
5 o
hm.
Seco
ndar
y C
oil.
-4,0
00 c
onvo
lutio
ns, t
he w
ire
havi
ng a
dia
met
er o
f 6
mils
and
a to
tal r
esis
tanc
e of
250
ohm
s.
154
Not
ts O
N tE
ttaltA
Pif
RE
CE
IVE
RS.
The
Bel
l tel
epho
ne a
lrea
dy d
escr
ibed
is a
uni
-pol
ar in
stru
men
t aS
Onl
yon
e po
le is
pre
sent
ed to
the
diap
hrag
m.
By
utili
sing
bot
h po
les
of th
em
agne
t, ho
wev
er, a
str
onge
r m
agne
tic f
ield
ispr
oduc
ed.
An
inst
rum
ent
cons
truc
ted
upon
this
pri
ncip
le is
term
eda
bi-p
olar
ordo
uble
pol
ete
leph
one.
The
mod
ern
form
of
Bel
l rec
eive
r, w
hich
has
been
ado
pted
by
the
Post
Off
ice
as a
sta
ndar
din
stru
men
t, co
ntai
ns in
an
ebon
ite c
ase
aho
rse
-sho
e sh
aped
per
man
ent
mag
net,
upon
the
pole
s of
whi
char
esc
rew
ed tw
o so
ft ir
on p
ole
-pie
ces.
Tw
o co
ils a
re p
lace
dup
on th
e la
tter,
and
are
wou
nd to
var
ious
resi
stan
ces-
usua
lly 1
20 to
200
ohm
s.T
he c
oils
and
core
s ar
e no
t cir
cula
r bu
tsl
ight
ly e
long
ated
, and
lie
para
llel w
ith e
ach
othe
r.T
his
arra
ngem
ent t
ends
topr
omot
e a
grea
ter
effi
cien
cyof
the
inst
rum
ent b
y co
ncen
trat
ing
a la
rger
num
ber
of li
nes
of f
orce
thro
ugh
the
cent
re o
f th
e di
aphr
agm
.
The
fer
roty
pe d
iaph
ragm
is h
eld
inpo
sitio
n by
the
ear
-pie
ce w
hich
scre
ws
on to
the
ebon
ite c
ase.
An
adju
stab
le s
crew
at t
he b
ack
of th
ein
stru
men
tre
gula
tes
the
dist
ance
bet
wee
nth
epo
le -
piec
es a
nd th
edi
aphr
agm
. The
latte
r sh
ould
be
quite
cle
ar o
f th
epo
le -
piec
es, b
ut a
scl
ose
to th
em a
s po
ssib
le w
ithou
t act
ual
cont
act.
The
coi
ls a
re c
onne
cted
with
two
term
inal
s at
the
end
of th
eeb
onite
cas
e.A
ske
tch
of th
ein
stru
men
t is
show
n in
Fig
. 87.
In c
limat
es h
avin
g a
grea
t var
iatio
n of
tem
pera
ture
, dif
ficu
lty is
fre
quen
tly e
xper
ienc
edby
the
cont
ract
ion
and
expa
nsio
nof
the
perm
anen
tm
agne
t.T
heeb
onite
case
,by
whi
chth
edi
aphr
agm
ishe
ld,
isno
tsu
bjec
tto
the
sam
eef
fect
s of
tem
pera
ture
var
iatio
n, a
nd th
eun
equa
l exp
ansi
on a
nd c
ontr
actio
nof
the
mag
net a
nd th
e ca
seca
use
the
dist
ance
bet
wee
n th
e di
aphr
agm
and
the
mag
net t
o fl
uctu
ate
with
the
rise
and
fal
l of
tem
pera
ture
.T
hem
agne
tin
the
ordi
nary
rec
eive
r is
fix
edat
its
end
rem
ote
from
the
diap
hrag
m, a
nd th
e m
axim
um e
ffec
t of
the
vari
atio
nis
exp
erie
nced
.T
hedi
ffic
ulty
is o
verc
ome
in th
e E
ricc
son
patte
rn, h
owev
er, b
y m
akin
g th
eat
tach
men
t to
the
case
at t
hedi
aphr
agm
end
, the
reby
allo
win
gfo
rte
mpe
ratu
re v
aria
tions
at t
he o
ppos
ite e
nd o
f th
em
agne
t.In
ano
ther
type
of
rece
iver
the
ebon
ite is
sub
stitu
ted
by a
met
al c
ase
havi
ng a
sim
ilar
co -
effi
cien
tof
tem
pera
ture
vari
atio
nas
the
mag
net.
The
dist
ance
bet
wee
n th
e di
aphr
agm
and
the
pole
-pi
eces
con
sequ
ently
rem
ains
unif
orm
.
Ade
r's R
ecei
ver
is a
mod
ific
atio
n of
the
doub
le p
ole
Bel
l rec
eive
r.T
hem
agne
t is
circ
ular
sha
ped,
and
ser
ves
as a
han
dle
for
the
inst
rum
ent.
The
coils
are
arr
ange
d up
on tw
o so
ft ir
onpo
le -
piec
es a
ttach
ed to
the
pole
s of
the
mag
net.
The
chi
ef f
eatu
re o
f th
is in
stru
men
tis
a s
omew
hat m
assi
veri
ng o
f ir
on te
rmed
the
sur-
exci
tate
ur o
rov
er -
exci
ter,
whi
ch is
pla
ced
upon
the
side
of
the
diap
hrag
m r
emot
e fr
om th
e co
ils.
The
obj
ect o
f th
eir
on r
ing
is to
con
cent
rate
the
lines
of
forc
e th
roug
h th
e di
aphr
agm
, The
NO
TE
S O
N T
EU
LG
RA
PHY
.15
5
theo
ry o
f th
e in
stru
men
t is
that
the
near
er th
e si
ze o
f th
e ar
mat
ure
appr
oach
es th
at o
fth
e m
agne
t the
gre
ater
is th
e m
utua
l ind
uctio
nbe
twee
n th
em.
It is
app
aren
t tha
t the
dia
phra
gm c
anno
t be
incr
ease
d in
size
with
out a
ffec
ting
its f
lexi
bilit
y, b
ut th
e ri
ng o
f ir
on, w
hich
act
s m
ag-
netic
ally
as
part
of
the
diap
hrag
m, s
erve
s th
e sa
me
purp
ose.
The
line
s of
FIG
. 87
forc
e of
a s
tron
g m
agne
tic f
ield
are
thus
con
cent
rate
d th
roug
h th
e di
a-ph
ragm
and
the
curr
ents
trav
ersi
ngth
e co
ils p
rodu
ce a
max
imum
eff
ect.
The
inst
rum
ent i
s hi
ghly
sen
sitiv
e, a
nd is
larg
ely
used
on
the
Con
tinen
t.
D' A
rson
val's
Rec
eive
r is
ano
ther
bi-
pola
r in
stru
men
t.T
he m
agne
t is
near
ly c
ircu
lar,
and
upo
n its
pol
es a
re f
itted
two
soft
iron
pol
e -p
iece
s.U
pon
one
of th
em a
coi
l is
plac
ed,
and
the
othe
r, w
hich
is v
irtu
ally
acy
linde
r, s
urro
unds
the
coil
and
its c
ore.
It w
ill th
us b
e se
en th
at th
e
142
NO
TE
S O
R T
EL
EG
RA
PHY
.
For
fast
spe
ed w
orki
ng s
hunt
edre
ceiv
ing
and
sign
allin
g co
nden
sers
are
also
em
ploy
ed. T
he u
se o
f th
e fo
rmer
tend
s to
neu
tral
ise
the
self
-ind
uctio
nof
the
rece
ivin
g ap
para
tus,
whi
le th
e fu
nctio
n of
the
latte
r is
to n
ullif
y th
eef
fect
s of
the
capa
city
of
the
line.
The
dis
char
ge f
rom
the
sign
allin
g co
n-de
nser
fill
s th
e ca
paci
ty o
f th
e ca
ble,
and
the
ordi
nary
wor
king
cur
rent
,w
hich
pas
ses
thro
ugh
the
shun
t, is
tim
edth
ereb
y to
rea
ch th
e ca
ble
whe
nth
e ca
paci
ty o
r "
swal
low
" o
f th
e lin
e ha
s be
en s
atis
fied
.
As
the
stat
ic c
apac
ity o
f a
cabl
e is
very
gre
at a
n op
posi
ng o
r ne
utra
lisin
gcu
rren
t, te
rmed
the
" cu
rbin
g "
curr
ent,
is a
utom
atic
ally
sen
t out
bet
wee
nea
ch s
igna
l.T
he c
able
is a
lso
put t
o ea
rth
by th
e sa
me
mov
emen
t aft
erea
ch c
urbi
ng c
urre
nt.
A v
ery
delic
ate
adju
stm
ent o
f th
ela
tter
to th
eor
dina
ry c
urre
nt is
nec
essa
ry, a
nd it
has
bee
n fo
und
that
the
prop
ortio
nof
the
curb
ing
curr
ent t
o th
e or
dina
ry c
urre
nt s
houl
d be
as 4
: 5
to e
nsur
eth
e be
st r
esul
ts.
NO
TE
S O
N T
EL
EG
RA
PHY
.14
3
CH
APT
ER
XIX
.
TH
E T
EL
EPH
ON
E.
The
idea
of
tran
smitt
ing
soun
ds to
a d
ista
nce
is s
ome
cent
urie
s ol
d, b
utit
was
not
unt
il th
e m
iddl
e of
the
nine
teen
th c
entu
ry th
at a
ttem
pts
wer
em
ade
to e
lect
rica
lly p
rodu
ce th
e de
sire
d ef
fect
s. T
he e
lect
rica
l tra
nsm
issi
onof
art
icul
ate
spee
ch, h
owev
er, w
as n
ot m
ade
a su
cces
s un
til th
e ye
ar 1
876,
whe
n th
e fi
rst "
spe
akin
g "
tele
phon
e w
as p
rodu
ced
by P
rofe
ssor
Gra
ham
Bel
l. Be
fore
atte
mpt
ing
to d
escr
ibe
this
inst
rum
ent,
som
e lit
tle a
ttent
ion
shou
ldbe
pai
d, p
erha
ps, t
o th
e ca
use
and
effe
ct o
f so
unds
.A
sou
nd is
pro
duce
dby
any
act
ion
whi
ch s
ets
up a
suf
fici
ently
vig
orou
s st
ate
of v
ibra
tion
in th
e ai
r.W
hen
a bo
dy v
ibra
tes,
the
vibr
atio
ns a
re c
omm
unic
ated
to th
e su
rrou
ndin
g ai
r, w
hich
is a
ltern
atel
y ra
refi
ed a
nd c
onde
nsed
by
the
mot
ion
of th
e vi
brat
ing
body
.W
hen
a tu
ning
for
k is
str
uck
the
pron
gsvi
brat
e at
a g
reat
rat
e, a
nd th
e ai
r in
thei
r im
med
iate
nei
ghbo
urho
od is
carv
ed in
to w
aves
whi
ch s
prea
d in
all
dire
ctio
ns.
The
se a
ir w
aves
, whi
chim
ping
e up
on th
e ty
mpa
num
or
drum
of
the
ear
and
caus
e it
to v
ibra
tein
syn
chro
nism
with
the
vibr
atin
g bo
dy, a
re c
onve
yed
to th
e au
dito
ryne
rves
and
the
sens
atio
n of
sou
nd is
thus
pro
duce
d.If
the
tuni
ng f
ork
had
been
cau
sed
to v
ibra
te in
a v
acuu
m th
ere
wou
ld h
ave
been
no
soun
d,as
the
med
ium
by
whi
ch s
ound
is tr
ansm
itted
wou
ld h
ave
been
abs
ent.
The
thre
e ch
arac
teri
stic
s by
whi
ch s
ound
s ar
e di
stin
guis
hed
from
one
anot
her
are
pitc
h, in
tens
ity, a
nd q
ualit
y or
tim
bre.
Pitc
h is
that
cha
ract
Lis
tic w
hich
det
erm
ines
the
note
of
a so
und.
Itde
pend
s up
on th
e nu
mbe
r of
vib
ratio
ns th
e so
undi
ng b
ody
perf
orm
s in
agi
ven
time.
The
hig
her
the
note
the
grea
ter
will
be
the
num
ber
of v
ibra
-tio
ns p
er s
econ
d, w
hile
for
a lo
wer
not
e a
few
er n
umbe
r of
vib
ratio
ns w
illbe
req
uire
d.In
tens
ity d
epen
ds u
pon
the
ampl
itude
of
the
vibr
atio
ns. W
hen
a tu
ning
fork
is s
truc
k it
vibr
ates
at t
he s
ame
rate
dur
ing
the
who
le o
f th
e tim
e th
evi
brat
ions
are
sus
tain
ed, h
ence
ther
e is
no
vari
atio
n in
the
note
.T
helo
udne
ss o
r in
tens
ity o
f th
e so
und,
how
ever
, dep
ends
upo
n th
e am
plitu
deof
the
vibr
atio
ns, o
r th
e di
stan
ce w
hich
the
pron
gs m
ove
in p
erfo
rmin
g a
com
plet
e vi
brat
ion.
The
vib
ratio
ns m
ay b
e se
en w
ith th
e na
ked
eye
whe
nth
e fo
rk is
fir
st s
truc
k, b
ut th
eir
ampl
itude
gra
dual
ly d
imin
ishe
s.T
heso
und
is lo
ud a
t fir
st a
nd s
low
ly d
ies
away
, unt
il, w
hen
the
pron
gs c
ease
to v
ibra
te, n
o so
und
is e
mitt
ed.
Qua
lity
or ti
mbr
e m
ay b
e be
st il
lust
rate
d by
pro
duci
ng th
e sa
me
note
on tw
o di
ffer
ent m
usic
al in
stru
men
ts,
Wne
n th
e sa
me
note
is p
rodu
ced
- #4
-
10N
on%
ON
TE
LE
GR
APH
Y.
The
dif
fere
nce
of p
oten
tial b
etw
een
zinc
and
cop
per
imm
erse
d in
liqu
idsu
ch a
s hy
droc
hlor
ic o
r su
lphu
ric
acid
, is,
rou
ghly
spe
akin
g, o
ne v
olt.
Bef
ore FIG
. 5.
II?
coil
a
Fl G
-.
TH
E S
IMPL
E C
EL
L.
Cop
per
(Cu)
and
zin
c (Z
n) a
ro th
e tw
o m
etal
s, o
r el
emen
ts, u
sed
in w
hat
is k
now
n as
the
sim
ple
cell,
and
thes
e ar
e pl
aced
in a
sui
tabl
e ve
ssel
, suc
has
gla
ss o
r gl
azed
ear
then
war
e, c
onta
inin
g pu
re w
ater
(H
20).
(Fig
. 7.)
A
fi co
FIG
. 7F
LG
. 8
So lo
ng a
s th
e pl
ates
are
kep
t sep
arat
e, a
nd n
o co
nduc
ting
wir
e co
nnec
tsth
em o
utsi
de th
e liq
uid,
no
curr
ent o
f el
ectr
icity
can
flo
w;
but t
he tw
ovi
eces
ofw
ire,
A a
nd B
, pos
sess
cer
tain
elec
tric
alpr
oper
ties
not
NO
TE
S O
N T
EL
EG
RA
PHY
.11
hith
erto
obs
erve
d in
them
, and
whi
ch,
for
conv
enie
nce,
are
term
edel
ectr
o-po
sitiv
e an
d el
ectr
o-ne
gativ
e.In
thes
e co
nditi
ons
itis
cle
ar th
atth
e ci
rcui
t is
inco
mpl
ete
;it
lack
s co
ntin
uity
, yet
a te
nden
cy e
xist
s ev
enno
w f
or a
cur
rent
to b
e ur
ged
thro
ugh
the
liqui
d of
the
oell,
sta
rtin
g fr
omth
e su
rfac
e of
the
zinc
pla
te.
Whe
n th
e w
ires
A a
nd B
are
join
ed, h
owev
er, a
s sh
own
in F
ig. 8
, an
elec
tric
cir
cuit
is e
stab
lishe
d, a
nd a
n un
brok
en p
ath
for
the
curr
ent m
ay b
etr
aced
fro
m it
s su
ppos
ed s
ourc
e, th
e zi
nc p
late
, thr
ough
the
liqui
d to
the
copp
er p
late
, alo
ng th
e co
nnec
ting
wir
e an
d ba
ck a
gain
to it
s st
artin
gpo
int.
The
arr
ows
indi
cate
the
path
and
dir
ectio
n of
the
curr
ent.
The
che
mic
al a
ctio
n se
t up
to p
rodu
ce th
is c
urre
nt m
ay b
e st
ated
as
follo
ws:
---
The
oxy
gen
(0)
atta
cks
the
zinc
and
com
bine
s w
ith it
, the
two
form
ing
zinc
oxi
lre
(Zn0
), w
hile
hyd
roge
n (H
) is
rel
ease
d, a
nd e
vent
ually
col
lect
sup
on th
e co
pper
pla
te, o
r is
giv
en o
ff a
s bu
bble
sat
the
surf
ace
of th
eliq
uid.
Rep
rese
nted
sym
bolic
ally
the
actio
n m
ay b
e ex
pres
sed
thus
:-B
efor
e co
ntac
t.A
fter
con
tact
.Z
n11
20 -
I- H
2O +
H2O
+ C
u =
Yin
° +
H2O
+ H
2O +
H2C
u.T
he a
ctio
n of
a c
ell o
f th
is k
ind
soon
cea
ses,
bec
ause
the
zinc
oxi
de f
orm
edis
a n
on-c
ondu
ctor
, and
is in
solu
ble
in w
ater
.T
he z
inc
plat
e be
com
esco
vere
d w
ith th
is in
sula
ting
com
poun
d, a
nd th
e ce
ll qu
ickl
y be
com
esin
activ
e.W
hen
dilu
te s
ulph
uric
aci
d is
sub
stitu
ted
for
pure
wat
er a
slig
htly
bet
ter
resu
lt is
obt
aine
d.T
he s
ulph
ion
(SO
4) o
f th
e su
lphu
ric
acid
(H
2SO
4)co
mbi
nes
with
the
zinc
, and
a s
alt o
f th
at m
etal
, zin
c su
lpha
te (
Zn
SO4)
is f
orm
ed, t
he r
esis
tanc
e of
the
cell
bein
g sl
ight
ly d
ecre
ased
. Zin
c su
lpha
teis
sol
uble
in w
ater
, and
, as
a co
nseq
uenc
e, th
e zi
nc p
late
is le
ft e
ntir
ely
clea
r, th
e ac
tion
of th
e ac
id u
pon
it be
ing
cont
inue
d. T
he n
asce
nt h
ydro
gen
rele
ased
by
this
act
ion
is v
ery
activ
e, a
nd im
med
iate
ly c
ombi
nes
with
the
sulp
hion
of
anot
her
mol
ecul
e of
sul
phur
ic a
cid.
The
se c
hang
es c
ontin
ueun
til a
film
of
hydr
ogen
is e
vent
ually
dep
osite
d up
on th
e co
pper
or
nega
tive
plat
e, w
hich
soo
n de
stro
ys th
e ut
ility
of
the
cell
by c
ausi
ng p
olar
isat
ion.
POL
AR
ISA
TIO
N.
Hyd
roge
n is
an
elec
trop
ositi
ve g
as ;
it is
ele
ctro
-pos
itive
to c
oppe
r, a
szi
nc is
, and
the
cond
ition
s be
com
e as
if tw
o si
mila
r pl
ates
wer
e op
pose
d to
each
oth
er, a
wea
keni
ng e
ffec
t upo
n th
e cu
rren
t is
quic
kly
appa
rent
, and
the
latte
r is
obs
erve
d to
dim
inis
h ra
pidl
y an
d ul
timat
ely
to c
ease
.A
stu
dy o
f Fi
g. 9
will
aid
the
read
er in
his
des
ire
to c
ompr
ehen
d th
ege
nera
lly a
ccep
ted
theo
ry o
f th
e si
mpl
e ce
ll, a
nd th
e ca
use
of p
olar
isat
ion.
In th
e sk
etch
the
mol
ecul
es o
f su
lphu
ric
acid
are
rep
rese
nted
elli
ptic
ally
,th
e sh
aded
por
tions
den
otin
g th
e hy
drog
en a
nd th
e un
shad
ed p
ortio
ns th
esu
lphi
on.
Ti
the
uppe
r ro
w e
ach
mol
ecul
e is
dep
icte
d as
bei
ng c
ompl
ete,
12N
OT
ES
ON
TE
LE
GR
APH
Y.
4
and
repr
esen
ts th
e co
nditi
ons
befo
re a
ctio
n ta
kes
plac
e, w
hils
t the
low
erro
w s
how
s th
e su
lphi
on a
ttack
ing
the
zinc
and
the
hydr
ogen
adh
erin
g to
the
surf
ace
of th
e co
pper
pla
te, t
he in
terc
hang
e of
part
ners
hav
ing
resu
lted
in th
e de
com
posi
tion
of o
ne m
olec
ule
of s
ulph
uric
aci
d.lf
avin
g de
scri
bed
how
a c
urre
nt o
f vo
ltaic
ele
ctri
city
may
be
gene
rate
d,i t
will
now
be
oppo
rtun
e to
pro
ceed
a li
ttle
furt
her
and
expl
ain
how
the
con-
stan
cy, o
r st
eadi
ness
, of
the
curr
ent e
man
atin
g fr
om a
com
bina
tion
of th
eki
nd a
lrea
dy d
escr
ibed
may
be
impr
oved
and
mai
ntai
ned
;fo
r it
is to
the
cons
tanc
y of
the
curr
ent p
rodu
ced
by a
cel
l tha
t its
chi
ef u
tility
is d
ue.
The
gre
at a
im, t
hen,
is to
des
troy
the
dele
teri
ous
effe
cts
of th
e fr
eehy
drog
en in
the
cell.
Hyd
roge
n ga
s of
fers
con
side
rabl
e re
sist
ance
to th
epa
ssag
e of
a c
urre
nt o
f el
ectr
icity
, and
is th
e di
rect
cau
se o
f po
lari
satio
n.If
a s
econ
d liq
uid
or a
sub
stan
ce w
ith w
hich
the
free
hyd
roge
n ca
nch
emic
ally
com
bine
is in
trod
uced
into
the
cell,
and
, by
such
com
bina
tion,
a ha
rmle
ss c
ompo
und
form
ed, t
hen
pola
risa
tion
prac
tical
ly c
ease
s.A
con
side
ratio
n of
the
Dan
iell
cell
will
fur
nish
a g
ood
inst
ance
of
such
am
etho
d al
lude
d to
abo
ve.
TH
E D
AN
IEL
L C
EL
L.
The
Dan
iell
cell
is c
ompr
ised
of
a zi
nc p
late
as
the
posi
tive
elem
ent,
and
a th
in s
heet
of
copp
er a
s th
e ne
gativ
e el
emen
t.T
he v
esse
l con
tain
ing
the
liqui
d is
eith
er d
ivid
ed in
to tw
o se
ctio
ns b
y a
poro
us p
artit
ion,
or
a po
rous
pot o
f un
glaz
ed p
orce
lain
is p
lace
d in
the
cont
aini
ng v
esse
l.In
to th
e po
rous
pot
is p
lace
d th
e co
pper
pla
te, a
nd a
sol
utio
n of
cop
per
sulp
hate
(C
u SO
4) s
urro
unds
the
plat
e, a
sm
all q
uant
ity o
f co
pper
sul
phat
ecr
ysta
ls b
eing
add
ed.
The
out
er v
esse
l con
tain
s di
lute
sul
phur
ic a
cid,
and
the
zinc
pla
teim
mer
sed
ther
ein.
NO
TE
S O
N T
EL
EG
RA
PHY
.13
The
sul
phur
ic a
cid
and
the
sulp
hate
of
copp
er, r
espe
ctiv
ely,
are
the
exci
ting
flui
d an
d th
e de
pola
risi
ng a
gent
, and
they
are
kep
t sep
arat
e by
the
poro
us p
artit
ion.
By
osm
otic
act
ion-
whi
ch is
the
tend
ency
of
two
diff
eren
t flu
ids,
sepa
rate
d by
a p
orou
s pa
rtiti
on, t
o m
ingl
e-th
e ou
ter
and
inne
r ce
lls a
rech
emic
ally
con
nect
ed.
The
sul
phio
n of
the
sulp
huri
c ac
id a
ttack
s th
e zi
nc p
late
, for
min
g, w
ithzi
nc, s
ulph
ate
of z
inc,
and
the
hydr
ogen
, rel
ease
d, e
nter
s in
to c
ombi
na-
'Mon
with
the
sulp
hion
of
the
sulp
hate
of
copp
er, p
rodu
cing
sul
phur
ic a
cid.
Pure
cop
per
inst
ead
of h
ydro
gen
is e
vent
ually
dep
osite
d up
on th
e co
pper
plat
e, w
hore
it p
rese
rves
a b
righ
t, cl
ean
surf
ace
of c
oppe
r, a
nd m
aint
ains
the
pote
ntia
l dif
fere
nce
betw
een
the
nega
tive
and
posi
tive
plat
es o
f th
ece
ll.,.
A v
ertic
al s
ectio
n of
the
Dan
iell
cell
is s
how
n in
Fig
. 10.
FIG
. 10.
Whe
n th
is c
ell i
s re
quir
ed f
or im
med
iate
use
a w
eak
solu
tion
of z
inc
sulp
hate
take
s th
e pl
ace
of th
e di
lute
sul
phur
ic a
cid
in th
e ou
ter
com
-pa
rtm
ent,
and
a sa
tura
ted
solu
tion
of c
oppe
r su
lpha
te is
pla
ced
in th
epo
rous
pot
. B
y th
is m
eans
hyd
roge
nis
exc
lude
d fr
om th
e ce
ll, a
ndpo
lari
satio
n en
tirel
y av
oide
d so
long
as th
e sa
tura
tion
of th
e co
pper
sulp
hate
is m
aint
aine
d.G
ener
ally
spe
akin
g, th
e ch
emic
al r
e -a
ctio
ns a
re th
e sa
me
as if
sul
phur
icac
id w
ere
used
.T
he z
inc
sulp
hate
atta
cks
the
zinc
pla
te, f
orm
ing
fres
hm
olec
ules
of
that
sal
t, an
d m
etal
lic z
inc,
inst
ead
of h
ydro
gen,
is li
bera
ted.
The
zin
c no
w s
et f
ree
deco
mpo
ses
the
copp
er s
ulph
ate
form
ing
mor
e zi
ncsu
lpha
te, a
nd li
bera
ting
pure
cop
per,
whi
ch is
dep
osite
d up
on th
e co
pper
plat
e,.
14,N
OT
ES
ON
TE
LE
GR
APH
Y.
The
che
mic
al a
ctio
n in
this
cas
e m
ay b
e sy
mbo
lical
ly e
xpre
ssed
thus
:-Z
nSO
4Zn
+ C
u SO
4 +
Cu
= Z
n2Z
n SO
4 -I
- C
u +
Cu
By
usin
g su
lpha
te o
f zi
nc in
stea
d of
sul
phur
ic a
cid
the
unne
cess
ary
was
te o
f th
e zi
nc p
late
is m
ater
ially
red
uced
.O
n ac
coun
t of
its c
onst
ancy
the
Dan
iell
cell
is k
now
n as
a "
sta
ndar
d "
cell,
with
an
olec
to-m
otiv
e fo
rce,
or
pote
ntia
l dif
fere
nce,
of
1.08
vol
t.
LO
CA
L A
CT
ION
.
In o
rdin
ary
com
mer
cial
zin
c m
any
and
vari
ous
extr
aneo
us s
ubst
ance
ssu
ch a
s pa
rtic
les
of c
arbo
n, le
ad, t
in, i
ron,
etc
., be
com
e em
bedd
ed d
urin
its m
anuf
actu
re. A
dif
fere
nce
of p
oten
tial b
etw
een
them
, and
als
o be
twee
n)th
e zi
nc p
late
and
thes
e pa
rtic
les,
con
sequ
ently
exi
sts,
and
min
ute.
curr
ent4
are
sot u
p w
hen
the
cell
shou
ld b
e qu
iesc
ent.
All
the
esse
ntia
ls f
or ti
ntba
tteri
es e
xist
,an
d un
nece
ssar
y w
aste
ofm
ater
ials
is c
ontin
uous
*.go
ing
on.
Thi
s ca
n be
obv
iate
d, h
owev
er, b
y fi
rst d
ippi
ng th
e zi
nc p
late
into
an
acid
for
cle
ansi
ng p
urpo
ses,
and
then
app
lyin
g m
ercu
ry to
its
surf
ace
with
a pi
ece
of f
lann
el o
r a
brus
h.A
n am
alga
m o
f m
ercu
ry a
nd z
inc
is th
usfo
rmed
as
a pa
ste,
and
the
fore
ign
part
icle
s ar
e su
rrou
nded
by
the
amal
gam
,zi
nc a
nd m
ercu
ry a
lone
rem
aini
ng in
con
tact
with
the
acid
.M
ercu
ry is
not
che
mic
ally
not
ed u
pon
by th
e ac
id, a
nd, t
here
fore
, doe
sno
t int
erfe
re w
ith th
e w
orki
ng o
f th
e ce
ll, f
or th
e ac
id a
cts
only
upo
n th
epa
rtic
les
of p
ure
zinc
).
TH
IS L
EC
LA
NC
HE
CE
LL
.
The
re a
ro th
roe
typo
s or
mod
ific
atio
ns o
f th
is c
ell w
hich
will
req
uire
atte
ntio
n :
(a)
ordi
nary
Loc
lanc
he ;
(b)
aggl
omer
ate
;, (
c)th
e dr
y ce
ll.(a
) T
he o
rdin
ary
.1 J
ecla
nch6
cel
l con
sist
s of
an
oute
r co
ntai
ning
ves
sel,
apo
rous
pot
, a z
ino
rod
as th
e po
sitiv
e el
emen
t, an
d a
slab
of
prep
ared
carb
on a
s th
e ne
gativ
e pl
ate.
The
exc
iting
flu
id is
a s
atur
ated
sol
utio
n of
sal a
mm
onia
c, o
r ch
lori
de o
f am
mon
ium
(N
114C
1), w
hils
t per
oxid
e of
man
gane
se (
Mn0
2) a
cts
as th
e de
pola
risi
ng a
gent
.T
he c
arbo
n pl
ate
is in
side
the
poro
us p
ot, a
nd is
sur
roun
ded
by g
ranu
les
of c
rush
ed c
arbo
n an
d pe
roxi
de o
f m
anga
nese
, all
dust
and
pow
dere
dca
rbon
bein
gca
refu
llyex
clud
edfr
omth
ece
ll.T
hezi
ncro
d,im
mer
sed
in th
e so
lutio
n of
sal
-am
mon
iac,
Is
plac
ed in
the
oute
r ve
ssel
.(S
ee F
ig. 1
1.)
In a
ctio
n th
e ch
lori
ne o
f th
e sa
l -am
mon
iac
com
bine
s w
ith th
e zi
nc,
form
ing
zinc
chl
orid
e (Z
nCl2
), a
mm
onia
(N
H3)
and
hyd
roge
n be
ing
cons
eque
ntly
rel
ease
d.A
larg
e qu
antit
y of
the
amm
onia
, how
ever
, is
dis-
solv
ed in
the
wat
er u
ntil
satu
ratio
n po
int i
s re
ache
d, a
fter
whi
ch c
ondi
tion
is a
rriv
ed a
t the
am
mon
ia e
scap
es a
s a
gas.
The
rel
ease
d hy
drog
en f
inds
its w
ay in
to th
e in
ner
vess
el a
nd c
ombi
nes
with
a p
ortio
n of
the
oxyg
en o
f
1lO
IO
tt T
EtE
GR
API
tY.
15
the
pero
xide
of
man
gane
se, r
educ
ing
the
latte
r to
a lo
wer
oxi
de (
Mn2
03),
and
form
ing
wat
er.
Rep
rese
nted
equ
atio
nally
the
actio
n of
this
cel
l is
:
Zn
2N11
401
2Mn0
2 =
ZnC
12+
011
2 +
Mn2
03.
Con
side
rabl
e ca
re is
nec
essa
ry in
the
cons
truc
tion
of th
e va
riou
s pa
rts
ofth
is c
ell.
The
zin
c ro
d ha
s ei
ther
a r
ubbe
r ri
ng a
t the
top
and
botto
m to
avoi
d co
ntac
t with
the
poro
us p
ot, o
r th
e up
per
port
ions
of
the
rod
and
pot a
re c
over
ed w
ith p
itch.
The
top
of th
e ca
rbon
is d
ippe
d in
mel
ted
para
ffin
wax
to c
lose
the
pore
san
d pr
even
t the
asc
ensi
on o
f th
e liq
uid
by c
apill
iary
attr
actio
n.A
lead
en
cap
is a
lso
fixe
d to
the
carb
on p
late
and
the
term
inal
scr
ew s
et in
the
lead
.C
oppe
r, b
rass
, and
suc
h -l
ike
met
als
are
read
ilyco
rrod
ed b
y sa
l -am
mon
iac
and
amm
onia
, whe
reas
lead
is n
ot v
ery
easi
ly a
ssai
led.
The
por
ous
cell
iscl
osed
by
a la
yer
of p
itch
to k
eep
the
nega
tive
elem
ent i
n po
sitio
n,bu
t
hole
s fo
r th
e es
cape
of
gase
s ar
e pi
erce
d th
roug
h th
e pi
tch.
The
ext
erio
r of
the
oute
r ve
ssel
sho
uld
be k
ept p
erfe
ctly
dry
, and
its to
pis
usu
ally
coa
ted
with
pitc
h to
pre
vent
the
sal -
amm
onia
c fr
om c
ryst
allis
ing
out -
a te
nden
cy th
at s
alt p
osse
sses
in a
mar
ked
degr
ee-w
hich
,if
per
-m
itted
, wou
ld r
esul
t iu
a lo
ss o
f m
ater
ial,
and
the
effi
cien
cyof
the
cell
wou
ld b
e co
nsid
erab
ly im
pair
ed.
18N
OT
ES
ON
TE
LE
GR
APH
Y.
(b)
The
agg
lom
erat
e L
ecla
nche
.In
this
type
of
Lec
lanc
he c
ell t
hepo
rous
pot
, whi
ch in
all
case
s in
trod
uces
com
para
tivel
y hi
gh r
esis
tanc
e,is
dis
pens
ed w
ith, a
nd th
e in
tern
al r
esis
tanc
e of
the
cell
is c
onse
quen
tlym
uch
redu
ced.
The
typo
kno
wn
as th
e "
6 -b
lock
agg
lom
erat
e "
is h
ere
desc
ribe
d.T
he n
egat
ive
elem
ent i
s a
bloc
k of
car
bon
havi
ng s
ix f
lute
d si
des.
Into
nach
rec
ess
is la
id a
n ag
glom
erat
ed r
od, m
ade
up o
f ca
rbon
and
man
gani
oox
ide;
the
who
le is
then
wra
pped
rou
nd w
ith a
pie
ce o
f ca
nvas
sac
king
.'T
wo
rubb
er b
ands
enc
ircl
e th
e ca
nvas
to k
eep
the
mat
eria
ls in
pos
ition
and
pres
erve
the
nece
ssar
y pr
essu
re b
etw
een
the
rods
and
the
carb
onbl
ock.
(Fig
. 12.
)T
he c
anva
s ac
ts in
the
sam
e w
ay a
s th
e po
rous
pot
by
FIG
. ii
perm
ittin
g th
e so
lutio
n to
com
e in
to c
onta
ct w
ith th
e ro
ds, a
nd p
reve
nts
" sh
ort c
ircu
iting
" in
eve
nt o
f po
rtio
ns o
f th
e ag
glom
erat
ed r
ods
beco
min
gde
tach
ed.
A z
inc
plat
e of
spe
cial
sha
pe p
artly
sur
roun
ds th
e ab
ove
com
-bi
natio
n, a
nd a
cts
as th
e po
sitiv
e el
emen
t of
the
cell.
The
gen
eral
con
-st
ruct
ion
of th
is f
orm
of
Lec
lanc
he r
esul
ts in
a c
onsi
dera
ble
redu
ctio
n of
its in
tern
al r
esis
tanc
e.(c
) T
he "
dry
" c
ell.
Thi
s fo
rm o
f ce
ll is
use
ful c
hief
ly o
n ac
coun
t of
its p
orta
bilit
y.It
is w
ithou
t liq
uid,
and
, con
sequ
ently
, the
re is
no
risk
of
NO
TE
S O
N T
EL
EG
RA
PHY
.17
spill
ing
corr
osiv
e so
lutio
ns.
The
ingr
edie
nts,
how
ever
, are
kep
t in
a m
oist
cond
ition
, for
, if
allo
wed
to b
ecom
e dr
y, th
e ce
ll w
ould
be
rend
ered
use
less
,as
che
mic
al a
ctio
n w
ould
cea
se, a
nd s
o lo
ng a
s th
e m
oist
ure
is w
ell m
ain-
tain
ed th
e in
tern
al r
esis
tanc
e is
kep
t low
.A
des
crip
tion
of th
e E
.C.C
.dr
y "
cell,
whi
ch is
an
impo
rtan
t pat
tern
of th
e ki
nd, i
s he
re g
iven
:-T
he c
onta
inin
g ve
ssel
is o
f zi
nc, a
nd a
cts
as th
e po
sitiv
e el
emen
t of
the
.cel
l. A
pas
te, c
ompo
sed
prin
cipa
lly o
f pl
aste
r of
Par
is, c
hlor
ide
of z
inc,
sal
-am
mon
iac,
and
wat
er, i
s th
en a
dded
to th
e su
rfac
e of
the
zinc
, and
for
ms
an in
side
coa
ting.
Aro
und
the
carb
on p
late
is a
thic
k pa
ste
mad
e up
of
carb
on, p
erox
ide
of m
anga
nese
, chl
orid
e of
zin
c, a
nd w
ater
.D
urin
g ac
tion
of th
e L
ecla
nche
cel
l it w
ill b
e re
mem
bere
d th
at c
hlor
ide
of z
inc
is f
orm
ed, a
nd th
is, t
oget
her
with
that
add
ed a
s pa
rt o
f th
e pa
stes
,pr
eser
ves,
to a
cer
tain
ext
ent,
the
nece
ssar
y m
oist
ure
ofth
e ce
ll.
The
ele
ctro
-mot
ive
forc
e of
a L
ecla
nche
cel
l is,
app
roxi
mat
ely,
1.5
vol
t ,bu
t the
inte
rnal
res
ista
nce
vari
es f
rom
-25
to 4
ohm
s, a
ccor
ding
to th
epa
ttern
of
the
cell
and
the
size
of
the
plat
es.
The
Lec
lanc
he c
ell
is v
ery
serv
icea
ble
whe
re o
nly
occa
sion
al u
seis
need
ed, b
ut w
hen
cons
tant
ly w
orke
d it
quic
kly
pola
rise
s on
acc
ount
of
the
pero
xide
of
man
gane
se n
ot y
ield
ing
its o
xyge
n fr
eely
eno
ugh
to a
rres
tth
e re
leas
ed h
ydro
gen.
The
cel
l qui
ckly
rec
over
s, h
owev
er, i
f al
low
ed to
rest
, and
no
was
te o
f m
ater
ials
take
s pl
ace
whe
n it
is o
ut o
f ac
tion.
Furt
herm
ore,
pol
aris
atio
n is
not
so
evid
ent i
f th
e ce
ll is
wor
ked
thro
ugh
ahi
gh e
xter
nal r
esis
tanc
e, f
or th
e cu
rren
t is
then
pro
port
iona
lly f
eebl
e, a
ndch
emic
al r
eact
ions
are
con
sequ
ently
muc
h re
duce
d.
1811
0112
S O
N T
ti.t0
41A
PIIY
,
TH
E B
ICH
RO
MA
TE
CE
LL
.
The
bic
hrom
ate
cell
is n
oted
for
its
high
ele
ctro
-mot
ive
forc
e an
d ce
iTh
para
tivel
y lo
w in
tern
al r
esis
tanc
e.In
the
" Fu
ller
" bi
chro
mat
e (F
ig. 1
3)th
e zi
nc, o
r po
sitiv
e el
emen
t, is
in th
e fo
rm o
f a
rod
cast
upo
n a
copp
er w
ire
and
wid
ened
at i
ts b
ase.
The
rod
is p
lace
d in
a p
orou
s po
t tog
ethe
r w
ith a
smal
l qua
ntity
of
mer
cury
. A s
olut
ion
of d
ilute
sul
phur
ic a
cid
is a
dded
as a
n ex
cita
nt.
The
mer
cury
asc
ends
the
zinc
rod
by
capi
lliar
y at
trac
tion
and
amal
ga-
mat
es w
ith it
, for
min
g an
am
alga
m o
f zi
nc a
nd m
ercu
ry.
Loc
al a
ctio
n by
this
mea
ns is
con
side
rabl
y di
min
ishe
d.T
he c
hem
ical
act
ion
of th
e bi
chro
mat
e ce
ll is
som
ewha
t com
plic
ated
,bu
t an
idea
may
be
gath
ered
fro
m th
e fo
llow
ing
equa
tions
:-In
ner
Col
l :3Z
n3H
2SO
4 =
3Z
n SO
4 +
3H
2.O
uter
cel
l : T
he n
egat
ive
plat
e is
car
bon,
and
. the
dep
olar
isin
g ag
ent,
whi
ch is
a m
ixtu
re o
fbi
chro
mat
e of
pota
sh (
K2C
r207
) an
d di
lute
sulp
huri
c ac
id, s
urro
unds
it, t
he c
hem
ical
rea
ctio
ns o
f w
hich
pro
duce
chro
mic
aci
d (H
2Cr0
1), a
nd s
ulph
ate
of p
otas
sium
(K
2SO
4).
The
latte
ris
a h
arm
less
pro
duct
, whi
le th
e ox
ygen
in th
e fo
rmer
arr
ests
the
hydr
ogen
and
form
s w
ater
:-
K2C
r207
H2S
O4
+ H
2O =
K2S
O4
2H2C
rO4
The
fin
al e
quat
ion
may
be
repr
esen
ted
thus
:-
3112
21I2
Or0
431
1250
4 =
Cr2
(SO
4)3
+ 8
H20
.
LA
TIM
ER
CL
AR
K'S
ST
AN
DA
RD
CE
LL
.
Thi
s ce
ll is
use
d as
a s
tand
ard
of e
lect
ro-m
otiv
e fo
rce,
con
sequ
ently
its
chie
f ut
ility
is in
mea
sure
men
ts a
nd c
ompa
riso
ns.
It s
houl
d ne
ver
be p
uton
" s
hort
cir
cuit
" no
r us
ed w
ith v
ery
low
ext
erna
l res
ista
nces
.T
hein
tern
al r
esis
tanc
eof
the
cell
isco
mpa
rativ
ely
high
;bu
tth
isis
imm
ater
ial c
onsi
deri
ng th
e hi
gh d
egre
e of
uni
form
ity o
fits
ele
ctro
-m
otiv
e fo
rce.
In s
ize
the
cell
is v
ery
smal
l, an
d its
mat
eria
ls a
re e
ssen
tially
pur
e.T
oen
sure
the
latte
r co
nditi
on b
oth
the
zinc
and
mer
cury
use
d in
itsco
nstr
uctio
n ar
e sp
ecia
lly p
repa
red.
The
out
er c
onta
inin
g ve
ssel
may
be
of g
lass
-a s
hort
, wid
e te
st tu
bean
swer
ing
the
purp
ose
very
wel
l. (F
ig. 1
4.)
A la
yer
of p
ure
dist
illed
mer
cury
,w
hich
act
s as
the
nega
tive
elem
ent,
is p
lace
d in
the
botto
m o
f th
e tu
be to
the
dept
h of
abo
ut h
alf
an in
ch.
Ove
r th
is is
pla
ced
a m
ixtu
re o
f m
ercu
rous
sulp
hate
and
a s
atur
ated
sol
utio
n of
zin
c su
lpha
te in
the
form
of
a th
ick
past
e.T
he p
ositi
ve e
lem
ent i
s of
pur
e zi
nc in
sert
ed in
the
past
e, a
nd a
copp
er c
onne
ctin
g w
ire
is s
olde
red
to th
e to
p of
the
zinc
rod
.A
pla
tinum
wir
e is
fus
ed in
to th
e bo
ttom
of
the
glas
s tu
be, o
ne e
nd b
eing
in c
onta
ct
NO
TE
S O
N T
EL
EG
RA
PHY
.19
with
the
mer
cury
insi
de th
e tu
be, a
nd th
e ot
her
end
proj
ectin
g to
for
m a
conn
ectio
n.T
he v
esse
l is
then
sea
led
with
a s
uita
ble
mix
ture
suc
h as
mar
ine
glue
.
Fl G
14-
.
The
che
mic
al a
ctio
n of
the
cell
resu
lts in
the
deco
mpo
sitio
n of
the
mer
curo
us s
ulph
ate,
and
pur
e m
ercu
ry is
dep
osite
d at
the
botto
m o
f th
ece
ll. T
he z
inc
rod
is a
ttack
ed b
y th
e su
lphi
on o
f th
e m
ercu
rous
sul
phat
e, a
ndsu
lpha
te o
f zi
nc is
for
med
.T
he r
esul
t of
this
che
mic
al a
ctio
n, it
will
be
seen
, is
to in
crea
se th
e qu
antit
y of
pur
e m
ercu
ry a
lrea
dyin
the
cell,
whi
lesu
lpha
te o
f zi
nc is
con
stan
tly b
eing
for
med
at t
he e
xpen
se o
f th
e po
sitiv
eel
emen
t.T
he e
lect
ro-m
otiv
e fo
rce
of C
lark
's c
ell i
s 1.
434
volt
; but
in o
rder
topr
eser
ve th
e un
ifor
mity
of
this
dif
fere
nce
of p
oten
tial t
he te
rmin
als
shou
ldne
ver
be p
ut o
n sh
ort c
ircu
it no
r jo
ined
to a
low
ext
erna
l res
ista
nce.
SUM
MA
RY
OF
CE
LL
S.
The
fol
low
ing
cond
ition
s ar
e th
e ch
ief
poin
ts to
be
aim
ed a
t in
the
con-
stru
ctio
n of
Vol
taic
cel
ls :-
1. H
igh
and
cons
tant
ele
ctro
-mot
ive
forc
e.2.
Low
inte
rnal
res
ista
nce.
3. F
reed
om f
rom
pol
aris
atio
n.4.
Loc
al a
ctio
n to
be
redu
ced
to a
min
imum
.5.
Che
ap a
nd d
urab
le m
ater
ials
.A
com
pari
son
of th
e pr
inci
pal c
ells
whi
ch h
ave
been
des
crib
ed m
ay b
em
ade
by a
per
usal
of
the
follo
win
g ta
ble
;-
8N
OT
ES
ON
TE
LE
GR
APH
Y.
be o
f lik
e po
lari
ty to
the
indu
cing
pol
e of
the
mag
net (
Fig.
4),
as
it is
impo
ssib
le to
obt
ain
a m
agne
t with
onl
y on
e po
le. N
fro
F1G
4
It w
ill n
ow h
e ap
pare
nt w
hy a
mag
net a
ttrac
ts a
pie
ce o
f ir
on.
The
iron
has
beco
me
an in
duce
d m
agne
t, an
d, a
s th
e un
like
pole
s ar
e af
ljace
nt, i
t'w
ill b
e so
on b
y th
e ap
plic
atio
n of
the
firs
t law
of
mag
netis
m, w
hich
say
s'.
that
unl
ike
mag
netic
pol
es a
ttrac
t eac
h ot
her,
that
mut
ual a
ttrac
tion
ensu
es.
Con
sequ
ently
indu
ctio
n al
way
s pr
eced
es a
ttrac
tion.
NO
TE
S O
N T
EL
EG
RA
PHY
.9
CH
APT
ER
II.
BA
TT
ER
Y C
EL
LS.
A c
urre
nt o
f el
ectr
icity
can
flo
w f
rom
one
poi
nt to
ano
ther
onl
y w
hen
adi
ffer
ence
of
pote
ntia
l exi
sts
betw
een
thos
e po
ints
, and
a c
ondu
ctor
, whi
chof
fers
res
ista
nce,
con
nect
s th
em.
Vol
ta d
isco
vere
d th
at m
ere
cont
act o
f di
ssim
ilar
met
als
prod
uced
adi
ffer
ence
of
elec
tric
al c
ondi
tion
betw
een
them
, and
he
form
ed a
" c
onta
ct/
seri
es "
by
arra
ngin
g se
vera
l met
als
in a
par
ticul
ar o
rder
, so
that
, by
plac
ing
any
pair
in c
onta
ct, t
heir
rel
ativ
e el
ectr
ical
con
ditio
ns c
ould
be
read
ily k
now
n.T
he "
ser
ies,
" in
clud
ing
carb
on, w
hich
is n
ot a
met
al, i
s as
fol
low
s-G
raph
ite o
r ca
rbon
.Pl
atin
um.
Silv
er.
Cop
per.
Iron
.L
ead.
Tin
.+
Zin
c.T
he f
irst
nam
ed in
the
" se
ries
" a
ssum
es w
hat i
s te
rmed
a n
egat
ive
pote
ntia
l to
thos
e fo
llow
ing,
and
the
last
nam
ed a
pos
itive
pot
entia
l to
all
thos
e pr
eced
ing
it, a
nd, f
or a
ny p
air,
the
near
er to
the
top
of th
e lis
t in
the
one
case
, and
to th
e bo
ttom
in th
e ot
her,
the
grea
ter
will
be
the
dige
renc
eof
pot
entia
l bet
wee
n th
em.
Car
bon
and
zinc
, for
inst
ance
, Whe
n in
con
tact
, will
pro
duce
a g
reat
erdi
ffer
ence
of
pote
ntia
l tha
n co
pper
and
zin
c, w
hile
, on
the
othe
r ha
nd,
carb
on a
nd p
latin
um, o
r tin
and
zin
c as
res
pect
ive
pair
s, w
ill c
ause
but
com
para
tivel
y lit
tle d
iffe
renc
e of
pot
entia
l. T
he s
igns
+ a
nd -
, sho
wn
inco
nnec
tion
with
the
seri
es, a
re u
sed
to d
enot
e po
sitiv
e an
d ne
gativ
e co
n-di
tions
res
pect
ivel
y ;
but i
t sho
uld
be a
lway
s un
ders
tood
that
thes
e te
rms
mer
ely
indi
cate
; a r
elat
ivel
y hi
gher
or
low
er e
lect
rica
l lev
el.
A s
impl
e ex
peri
men
t sho
win
g th
at m
ere
cont
act o
f di
ssim
ilar
met
als
prod
uces
a d
iffe
renc
e of
ele
ctri
cal c
ondi
tion
has
been
mad
e by
Lor
d K
elvi
n,w
hich
pla
ces
Vol
ta's
theo
ry b
eyon
d di
sput
e.A
thin
str
ip o
f m
etal
, ele
ctri
fied
fro
m a
kno
wn
sour
ce, i
s su
spen
ded
soas
to tu
rn a
bout
a p
oint
" C
" (F
ig. 5
).U
nder
it a
re p
lace
d tw
o se
mi-
circ
ular
dis
cs o
f di
ssim
ilar
met
als,
A, B
.N
eith
er a
ttrac
tion
nor
repu
lsio
nof
the
stri
p ta
kes
plac
e un
til th
e di
scs
are
brou
ght i
nto
cont
act (
Fig.
6),
or
join
ed b
y a
wir
e, w
hen
attr
actio
n an
d re
puls
ion
imm
edia
tely
ens
ue.
158
NO
TE
S O
N T
EL
EG
RA
PHY
.
draw
n aw
ay f
rom
the
scre
w. T
he c
ontin
uity
of
the
circ
uit i
s th
usbr
oken
and
the
arm
atur
e, h
avin
g be
en r
elea
sed,
fal
ls b
ack.
The
cir
cuit
is c
onse
quen
tlyag
ain
join
ed u
p, b
ut is
bro
ken
imm
edia
tely
by
a fu
rthe
r at
trac
tion
of th
ear
mat
ure.
A tr
embl
ing
or v
ibra
ting
mot
ion
is th
usim
part
ed to
the
ham
mer
and
a c
ontin
uous
rin
ging
is s
etup
.T
he b
ody
of th
e in
stru
men
tis
enc
lose
d in
a w
oode
n ca
se to
shi
eld
it fr
omdu
st, w
hich
is a
fre
quen
tso
urce
of
trou
ble
if a
llow
ed to
lodg
e be
twee
n th
e co
ntac
tsc
rew
and
spr
ing.
The
coi
ls a
re u
sual
ly w
ound
to a
res
ista
nce
of a
bout
100
ohm
s.T
heri
ngin
g of
the
bell
is c
ontr
olle
d by
a p
ress
-bu
tton,
whi
ch is
sim
ply
a de
vice
for
join
ing
up th
e ba
ttery
.T
he la
tter
usua
lly c
onsi
sts
of a
sui
tabl
enu
mbe
r of
Lec
lanc
he c
ells
, whi
ch a
re b
ette
rad
apte
d fo
r ri
ngin
g pu
rpos
esth
an o
ther
type
s.T
he B
ichr
omat
e an
d D
anie
ll ce
llsar
e su
bjec
t to
loca
lac
tion
whe
n ou
t of
use,
and
con
sequ
ently
are
not f
itted
for
inte
rmitt
ent
wor
king
.
The
Mag
neto
Bel
l is
an in
stru
men
t whi
ch is
act
uate
dby
alte
rnat
ing
curr
ents
. Its
mai
n fe
atur
e is
that
the
arm
atur
e is
mag
netis
ed in
duct
ivel
yby
a p
erm
anen
t mag
net i
n su
ch a
man
ner
as to
ren
der
its e
xtre
miti
es o
fsi
mila
r po
lari
ty.
The
act
ion
of th
e be
ll w
ill b
e re
adily
und
erst
ood
byre
fere
nce
to F
ig. 8
9, in
whi
ch N
S is
a pe
rman
ent m
agne
t.T
he s
outh
-se
ekin
g po
le o
f th
e la
tter
acts
indu
ctiv
ely
upon
the
arm
atur
e A
B,
and
prod
uces
sout
h -s
eeki
ngpo
les
atth
een
ds.
The
arm
atur
e
ispi
vote
dat
itsce
ntre
, and
am
etal
rod
isat
tach
edat
that
poin
t.T
he r
od te
rmin
ates
in a
bra
ss b
all,
H, w
hich
pla
ys b
etw
een
two
gong
s, M
M.
Whe
nal
tern
atin
gcu
rren
tspa
ssth
roug
hth
e co
ils o
f th
e el
ectr
o-m
agne
t the
pol
es o
f th
e la
tter
are
reve
rsed
with
ever
y ch
ange
in th
e di
rect
ion
of th
e cu
rren
t.It
will
, the
refo
re, b
e se
enth
at w
hen
the
end
of th
e ar
mat
ure
at A
is a
ttrac
ted
by th
e ad
jace
nt n
orth
-
seek
ing
pole
of
the
elec
tro-
mag
net t
he e
nd B
and
the
sout
h -s
eeki
ng p
ole
ofth
e el
ectr
o-m
agne
t will
be
mut
ually
rep
elle
nt.
A r
ever
sal o
f th
e cu
rren
tca
uses
the
forc
es o
f at
trac
tion
and
repu
lsio
n to
cha
nge
plac
es, a
nd th
e
NO
TE
S O
N T
EL
EG
RA
PHY
.15
0
actio
n of
an
alte
rnat
ing
curr
ent w
ill th
eref
ore
prod
uce
a vi
brat
ory
mot
ion
of th
e pi
vote
d ar
mat
ure,
and
the
ham
mer
H w
ill o
scill
ate
betw
een
the
gong
s, s
trik
ing
each
in tu
rn.
The
coi
ls a
re w
ound
to a
res
ista
nce
of1,
000
ohm
s.
The
Mag
neto
Gen
erat
or is
use
d in
con
junc
tion
with
the
mag
neto
bel
l.It
s fu
nctio
n is
to s
uppl
y al
tern
atin
g cu
rren
ts in
ret
urn
for
mec
hani
cal
ener
gy e
xpen
ded
in tu
rnin
g a
cran
k ha
ndle
. A s
tron
g m
agne
tic f
ield
is p
ro-
duce
d by
mea
ns o
f th
ree
or m
ore
pow
erfu
l per
man
ent h
orse
sho
e m
agne
ts,
whi
ch h
ave
thei
r si
mila
r po
les
adja
cent
and
con
nect
ed b
y po
le -
piec
es. T
hein
ner
side
s of
the
latte
r ar
e cu
rved
and
bet
wee
n th
em a
piv
oted
arm
atur
e,
FIG
. 'C
I,
carr
ying
a c
oil o
f in
sula
ted
copp
er w
ire,
is r
apid
ly r
evol
ved
by m
eans
of
acr
ank
hand
le a
n ds
uita
ble
gear
in g
whe
els.
The
arm
atur
e is
rea
lly a
pec
ulia
rly
-sh
aped
ele
ctro
-mag
net,
the
core
of
whi
ch is
a s
oft i
ron
cylin
der
havi
ng tw
ow
ide
and
deep
gro
oves
, in
whi
ch th
e co
il is
wou
nd, r
unni
ng a
long
its
leng
th.
The
end
s pr
actic
ally
for
m th
e le
tter
H, a
nd th
e ar
mat
ure
is te
rmed
Sie
men
'sII
-sha
ped
arm
atur
e. W
hen
it is
in s
uch
a po
sitio
n th
at th
e pa
rts
of th
ecy
linde
r w
hich
for
m th
e si
des
of th
e le
tter
H a
re p
erpe
ndic
ular
, the
line
sof
for
ce b
ridg
e th
e sm
all a
ir -
gaps
bet
wee
n th
em a
nd th
e po
le -
piec
es,
and
pass
thro
ugh
the
part
for
min
g th
e ho
rizo
ntal
of
the
lette
r H
.T
his
posi
tion
is s
how
n in
Fig
.90
.W
hen
the
arm
atur
e ha
s be
en tu
rned
aqu
arte
rof
are
volu
tion,
the
curv
edsi
des
ofth
ecy
linde
r
160
NO
TE
S O
N T
EL
EG
I1A
PHY
.
near
ly b
ridg
e th
e sp
ace
betw
een
the
pole
-pi
eces
, and
the
maj
ority
of
the
lines
of
forc
e co
nseq
uent
ly f
ollo
w th
is p
ath.
It w
ill, t
here
fore
, be
seen
that
whi
le th
e ar
mat
ure
is in
mot
ion,
ther
e is
a c
ontin
uous
red
istr
ibut
ion
of th
e lin
es o
f fo
rce,
and
the
maj
ority
of
the
latte
r in
thei
r tr
ansi
tion
cut
thro
ugh
the
coil,
fir
st in
one
dir
ectio
n, a
nd th
en in
the
othe
r.T
hene
cess
ary
elec
tro-
mot
ive
forc
es f
or p
rodu
cing
alte
rnat
ing
curr
ents
are
thus
set u
p.O
ne e
nd o
f th
e co
il is
con
nect
ed w
ith th
e sp
indl
e of
the
arm
atur
e,an
d th
e ot
her
is jo
ined
by
mea
ns o
f an
insu
late
d sc
rew
with
a p
in, w
hich
pass
es in
to th
e sp
indl
e, b
ut is
insu
late
d fr
om it
by
an e
boni
te s
leev
e.T
here
sist
ance
of
the
coil
is 2
00 o
hms,
and
a g
ood
gene
rato
r w
ill r
ing
a m
agne
tobe
ll th
roug
h a
resi
stan
ce o
f 10
,C00
ohm
s.
.1>
LIN
E o
EI
LIN
E O
R, E
1FI
G
As
it is
und
esir
able
for
the
coil
of th
e in
stru
men
t to
be in
the
path
of
curr
ents
com
ing
from
the
line
man
y in
geni
ous
auto
mat
ic "
cut
-out
s "
have
bee
n de
vise
d.O
ne o
f th
ese
cons
ists
of
a sw
itch,
or
spri
ng, w
hich
norm
ally
sho
rt-c
ircu
its th
e co
il, b
ut im
med
iate
ly th
e ha
ndle
is tu
rned
the
posi
tion
ofth
e sw
itch
is a
ltere
d.B
y th
is m
eans
the
shor
t-ci
rcui
t is
auto
mat
ical
ly r
emov
ed a
nd th
e in
duce
d cu
rren
ts le
ave
the
inst
rum
ent a
ndtr
aver
se th
e lin
e.
The
con
nect
ions
of
a te
leph
one
set o
f th
e si
mpl
est d
escr
iptio
n ar
e sh
own
in F
ig. 9
1.T
he r
ecei
ver
-res
ts, s
how
n at
the
side
s of
the
diag
ram
, are
aut
o-m
atic
sw
itche
s w
hich
exc
lude
all
appa
ratu
s ex
cept
that
use
d fo
r ri
ngin
gpu
rpos
es w
hen
the
rece
iver
s ar
e in
pos
ition
.T
he s
peak
ing
appa
ratu
sis
join
ed u
p au
tom
atic
ally
by
the
leve
rs o
fth
e sw
itche
s fa
lling
bac
kan
d m
akin
g co
ntac
t with
the
back
sto
ps w
hen
the
rece
iver
s ar
e re
mov
ed.
NO
TE
S O
N T
EL
EG
RA
PHY
.16
1
The
spe
akin
g ba
ttery
is c
ompo
sed
of tw
o A
gglo
mer
ate
Lec
lanc
hece
lls,
and
the
ring
ing
batte
ry o
f a
grea
ter
num
ber
ofor
dina
ry L
ecla
nche
cel
lsjo
ined
in s
erie
s w
ith th
em.
Mod
ern
auto
mat
ic s
witc
hes
are
prov
ided
with
two
sets
of
cont
act s
prin
gs, a
nd o
ne s
witc
hse
rves
the
purp
ose
of th
etw
o sh
own
in F
ig. 9
1.T
he tw
o re
ceiv
ers
are
join
ed in
par
alle
l, bu
t, of
cour
se, o
ne o
nly
is n
eces
sary
; w
ith th
e do
uble
for
m o
f sw
itch
only
one
rece
iver
is e
mpl
oyed
.T
he te
leph
one
set s
how
n in
the
sket
ch is
inte
nded
to in
dica
te th
e po
sitio
n of
the
vari
ous
piec
es o
fap
para
tus,
and
is in
tro-
duce
d on
acc
ount
of
its s
impl
icity
.
c,'
156
NO
TE
S O
N T
EL
EG
RA
PHY
.
who
le o
f th
e co
il is
in th
e in
ter -
pola
r sp
ace
thro
ugh
whi
ch th
e lin
es o
ffo
rce
of th
e m
agne
t are
con
cent
rate
d.T
he o
bjec
t of
this
arr
ange
men
t is
to h
ave
the
who
le o
f th
e co
il in
the
mos
tin
tens
e pa
rt o
f th
e m
agne
tic)
fiel
d.In
the
ordi
nary
rec
eive
rsha
ving
two
coils
, onl
y th
e pa
rts
of th
eco
ils ly
ing
betw
een
the
two
pole
-pi
eces
are
eff
ectiv
e fo
rpu
rpos
esof
indu
ctio
n, w
here
as th
ose
port
ions
whi
char
e re
mot
e fr
om th
e in
ter
-pol
arsp
ace
are
prac
tical
ly o
ut o
f th
e m
agne
tic f
ield
, and
intr
oduc
ea
resi
stan
cew
ithou
t any
cor
resp
ondi
ngad
vant
age.
In th
e D
'Ars
onva
l rec
eive
r, h
ow-
ever
, the
who
le o
f th
e on
e co
il lie
s be
twee
n th
ece
ntra
l cor
e an
d th
eou
ter
shel
l.T
he c
oil a
nd p
ole
-pie
ces
are
encl
osed
in a
cas
e, w
hich
car
ries
the
ferr
otyp
e di
aphr
agm
.T
he m
agne
t ser
ves
the
purp
ose
of a
han
dle,
and
the
inst
rum
ent i
s pr
oduc
tive
ofve
ry g
ood
resu
lts.
NO
TE
S O
N T
EL
EG
RA
PHY
.15
7
CH
APT
ER
XX
.
AU
XIL
IAR
Y A
PPA
RA
TU
S.
The
Tre
inU
er B
ell i
s, p
erha
ps, t
hesi
mpl
est d
evic
e fo
r ga
inin
g at
tent
ion.
It c
onsi
sts
esse
ntia
lly o
f an
elec
tro-
mag
net a
rran
ged
upon
an
iron
fra
me,
whi
ch is
scr
ewed
to a
sto
ut b
ase
-boa
rd.
The
fra
me
carr
ies
a so
ft ir
onar
mat
ure
upon
a s
teel
spr
ing.
The
arm
atur
e pl
ays
in f
ront
of
the
pole
s of
the
elec
tro-
mag
net a
nd te
rmin
ates
in a
met
al r
od c
arry
ing
a br
ass
ham
mer
.T
he la
tter
beat
sup
on th
e go
ng w
hich
is s
uppo
rted
upo
n
an ir
on p
illar
.T
he a
rmat
ure
carr
ies
a lig
ht c
onta
ct s
prin
g w
hich
norm
ally
pre
sses
agai
nst
anin
sula
ted
adju
stab
leco
ntac
tsc
rew
.T
wo
term
inal
sar
e. f
ixed
toth
eba
se -
boa
rdan
dth
ecu
rren
tpa
sses
thro
ugh
the
elec
tro
- m
agne
tco
ilsan
dco
ntac
tsc
rew
and
spri
ng.
The
con
nect
ions
of
the
inst
rum
ent a
re in
dica
ted
in F
ig. 8
F.T
he a
ctio
n of
the
bell
is v
ery
sim
ple.
The
pas
sage
of
the
curr
ent t
hrou
ghth
e co
ils c
ause
s th
e at
trac
tion
of th
e ar
mat
ure
and
the
cont
act s
prin
g to
be
164
NO
TE
S O
N T
EL
EG
RA
PHY
.
part
ial c
olla
pse
of th
e lin
es o
f fo
rce,
but
, as
the
dire
ctio
n of
thei
r m
ove-
men
t will
be
sim
ilar
to th
at p
rodu
ced
by th
e ce
ssat
ion
of th
e pr
imar
ycu
rren
t, th
e di
rect
ion
of th
e in
duce
d cu
rren
t will
not
be
alte
red.
Whe
n th
e pr
imar
y cu
rren
t is
star
ted
or in
crea
sed
in s
tren
gth
the
indu
ced
curr
ent t
akes
an
oppo
sing
cou
rse
to it
.W
ith th
e ce
ssat
ion
orde
crea
se in
the
stre
ngth
of
the
prim
ary
curr
ent t
he in
duce
d cu
rren
t is
ina
sim
ilar
dire
etio
n to
that
of
the
indu
cing
cur
rent
.T
he e
ffec
ts a
re s
how
ndi
agra
mat
ical
ly in
Fig
s. 9
5 an
d 96
.
If in
duct
ion
take
s pl
ace
betw
een
two
tele
phon
e ci
rcui
ts "
ove
rhea
ring
"or
" c
ross
-ta
lk"
resu
lts. T
he in
duce
d cu
rren
ts r
ise
and
fall
in s
ynch
roni
smw
ith th
e pr
imar
y cu
rren
ts, a
nd th
e re
ceiv
ers
of th
e ci
rcui
t whi
ch is
acte
d up
on in
duct
ivel
y re
spon
d ac
cord
ingl
y.T
he c
hief
cau
se o
f ov
er-
hear
ing,
how
ever
, is
leak
age
from
one
cir
cuit
to a
noth
er, b
ut th
is is
obvi
ated
by
the
prec
autio
n of
" e
arth
wir
ing,
" w
hich
is d
ealt
with
in th
ech
apte
r de
vote
d to
the
cons
truc
tion
of a
eria
l lin
es.
The
eff
ects
of
indu
ctio
n ar
e ov
erco
me
by d
ispe
nsin
g w
ith th
e ea
rth
retu
rn a
nd u
sing
a m
etal
lic lo
op.
The
cir
cuit
is s
o ar
rang
ed th
at th
ein
duce
d cu
rren
ts a
re e
qual
in b
oth
wir
es o
f th
e lo
op, a
nd w
ill n
eutr
alis
e
E 4
--11
11?E
FIG
. 96.
E
each
oth
er a
t the
end
s of
the
circ
uit w
here
the
rece
iver
s ar
e si
tuat
ed.
To
ensu
re th
e ef
fect
of
com
plet
e ne
utra
lisat
ion,
the
two
wir
es f
orm
ing
the
met
allic
loop
mus
t be
alik
e in
all
resp
ects
.T
he c
ircu
it is
then
sai
d to
be
bala
nced
, and
sho
uld
fulf
il th
e fo
llow
ing
cond
ition
s :-
1. T
he w
ires
of
the
loop
mus
t mai
ntai
n th
roug
hout
the
sam
e av
erag
edi
stan
ce f
rom
the
indu
cing
hol
ies,
2. T
hey
shou
ld b
e of
the
sam
e m
ater
ial a
nd h
ave
the
sam
e co
nduc
tivity
.3.
The
ele
ctrc
-sta
tic c
apac
ity o
f th
e tw
o w
ires
sho
uld
be e
qual
.4.
The
co
-eff
icie
nt o
f se
lf-i
nduc
tion
of th
e tw
o w
ires
sho
uld
be th
e sa
me.
5. T
he w
ires
sho
uld
poss
ess
the
sam
e de
gree
of
insu
latio
n, h
igh
or lo
w.
6. T
he r
esul
tant
fau
lts d
ue to
impe
rfec
t ins
ulat
ion
shou
ld b
e at
the
sam
e di
stan
ces
elec
tric
ally
alo
ng e
ach
wir
e fr
om th
e en
ds o
f th
e ci
rcui
t.
!jhe
fir
st c
ondi
tion
isfu
lfill
ed b
y sy
mm
etri
cally
twis
ting
the
wir
esth
roug
hout
thei
r w
hole
leng
th T
he e
ffec
ts o
f in
duct
ion
will
then
be
sim
ilar
in b
oth
wir
es.
With
sta
tic in
duct
ion
the
po e
ntia
ls in
duce
d in
bot
h of
the
lines
for
min
g th
e lo
op w
ill b
e eq
ual.
If, h
owev
er, o
ne o
f th
e w
ires
sho
uld
be.
NO
TE
S O
N T
EL
EG
RA
PHY
%16
5
near
er th
e in
duci
ng b
ody
than
the
othe
r, th
e ef
fect
wou
ld b
e to
pro
duce
uneq
ual i
nduc
ed p
oten
tials
, and
cur
rent
s w
ould
flo
w f
rom
the
line
ofhi
gher
pote
ntia
lto
that
ofth
elo
wer
inor
der
tore
stor
eel
ectr
ical
equ
ilibr
ium
.T
hese
cur
rent
s, o
f ne
cess
ity, w
ould
pas
s th
roug
h
,7th
e en
ds o
f th
e ci
rcui
t and
act
uate
the
rece
iver
s, a
nd a
sile
nt c
ircu
itw
ould
be
impo
ssib
le in
the
vici
nity
of
othe
r w
ires
.C
onsi
deri
ng d
ynam
icin
duct
ion
the
mag
netic
fie
ld is
mos
t int
ense
nea
r th
e co
nduc
tor
carr
ying
the
indu
cing
cur
rent
.If
, the
refo
re, t
he li
nes
of th
e m
etal
lic c
ircu
it ar
e at
166
tuiT
2sop
tT
nttG
RA
tliq.
uneq
ual d
ista
nces
fro
m th
e in
duci
ng w
ire
the
one
whi
ch is
nea
rer
to it
iscu
t by
mor
e lin
es o
f fo
rce
than
the
othe
r.T
he in
duce
d el
ectr
o-m
otiv
efo
rce
is p
ropo
rtio
nal t
o th
e in
tens
ity o
f th
em
agne
tic f
ield
, and
, as
a co
nse-
quen
ce, t
he c
urre
nts
are
uneq
ual i
n st
reng
th a
nd c
ompl
ete
neut
ralis
atio
nis
not
eff
ecte
d.If
, how
ever
, the
con
ditio
ns a
re s
uch
as to
pro
duce
equa
lel
ectr
omot
ive
forc
es th
e in
duce
d cu
rren
ts n
ullif
y ea
chot
her,
and
the
ill-
effe
cts
of th
e in
duct
ion
are
over
com
e.
In c
onst
ruct
ing
tele
phon
e lin
es tw
o pa
irs
ofw
ires
, i.e
., tw
o m
etal
licci
rcui
ts, a
re r
evol
ved
one
roun
d th
e ot
her,
thus
mak
ing
the
indi
vidu
alw
ires
of
each
cir
cuit
at th
e sa
me
aver
age
dist
ance
fro
m th
e ea
rth
and
all
othe
r w
ires
car
ried
by
the
sam
e lin
e of
pol
es.
The
fou
r w
ires
are
at t
heco
rner
s of
a p
erfe
ct s
quar
e, th
ose
at th
e op
posi
te a
ngle
s be
ing
the
wir
es o
fa
loop
.T
he r
elat
ive
posi
tions
of
the
wir
eson
the
arm
s w
ill b
e un
der-
stoo
d fr
om F
ig. 9
7, in
whi
ch th
e w
ires
num
bere
d 1
and
3 fo
rmon
e ci
rcui
tan
d 2
and
4 th
e ot
her.
It w
ill b
e se
en th
at in
fou
rsp
ans
one
com
plet
ere
volu
tion
ism
ade.
Ifm
ore
than
two
circ
uits
are
upon
the
sam
e po
les
mor
e sq
uare
sar
e fo
rmed
and
the
cond
ucto
rs s
imila
rly
revo
lved
.It
will
beno
ticed
,ho
wev
er,
that
the
wir
esw
hich
occu
pysi
mila
rpo
sitio
nsin
the
squa
res
are
para
llel
and
over
hear
ing
may
be
expe
cted
to r
esul
t.T
his
is o
verc
ome
by c
ross
ing
the
wir
es o
f th
e lo
ops
form
ing
one
of th
esq
uare
s at
cer
tain
set
dis
tanc
es, s
oas
to m
ake
the
two
wir
es o
f ea
ch c
ircu
it th
e sa
me
aver
age
dist
ance
fro
mth
e ot
her
set o
f w
ires
.If
a la
rge
nuin
ber
of c
ircu
its r
unto
geth
er m
any
such
cro
sses
will
be
nece
ssar
y in
ord
er to
mak
e ea
ch c
ircu
iteq
uidi
stan
tfr
om a
ll th
e ot
hers
.T
his
met
hod
of c
ross
ing
is c
alle
d th
e "
cros
s -o
ver
"sy
stem
.It
is e
ffec
ted
by u
sing
dou
ble
sets
of
insu
lato
rson
the
arm
sw
here
the
cros
ses
are
mad
e.
Con
ditio
ns 2
and
3 a
re e
asily
ful
fille
d.A
cop
per
cond
ucto
r is
inva
riab
lych
osen
for
long
tele
phon
e ci
rcui
ts a
nd, o
f co
urse
, bot
h w
ires
of
the
loop
hav
eth
e sa
me
spec
ific
res
ista
nce
and
are
sim
ilar
in g
auge
.T
he r
esis
tanc
e an
dst
atic
cap
acity
of
each
line
will
con
sequ
ently
be
the
sam
e. P
hosp
hor
-bro
nze
and
silic
ium
-bro
nze,
whi
ch a
re a
lloys
of
copp
er, a
re f
requ
ently
use
d fo
rsu
bscr
iber
s' li
nes.
The
y co
ntai
n ab
out 3
per
cen
t. of
tin
in th
eir
com
posi
-tio
n, a
nd a
re u
sed
on a
ccou
nt o
f th
eir
grea
t ten
sile
str
engt
h.T
he r
esis
t-an
ce o
f al
loys
, how
ever
, is
com
para
tivel
y hi
gh, a
nd th
ese
cond
ucto
rs a
reco
nseq
uent
ly p
recl
uded
fro
m b
eing
use
d fo
r ci
rcui
ts o
f co
nsid
erab
le le
ngth
.Ir
on w
ires
are
rar
ely
used
for
tele
phon
e ci
rcui
ts.
The
spe
cifi
c re
sist
ance
of
iron
is a
bout
5i t
imes
that
ofco
pper
, and
inor
der
tore
plac
ea
copp
er w
ire
by o
ne o
f ir
on, t
he a
rea
of c
ross
sec
tion
of th
e la
tter
wou
ld b
e5i
tim
es a
s gr
eat a
s th
e fo
rmer
in o
rder
to m
aint
ain
the
sam
e re
sist
ance
.T
he s
trai
n up
on th
e su
ppor
ts, t
here
fore
, wou
ld b
e m
uch
grea
ter
in th
eca
se o
f th
e ir
on c
ondu
ctor
, and
, in
addi
tion
to th
is, t
he c
apac
ity o
f th
eci
rcui
t wou
ld b
e in
crea
sed,
as
the
wir
e, a
ctin
g as
one
pla
te o
f a
cond
ense
r,w
ould
be
enla
rged
.E
lect
ro-m
agne
tic in
ertia
, whi
ch is
pra
ctic
ally
abs
ent
NO
TE
S O
N T
EL
EG
RA
PHY
.16
7
in a
cop
per
cond
ucto
r, is
con
side
rabl
e in
the
case
of
iron
, and
this
isan
othe
r po
tent
rea
son
in f
avou
r of
cop
per.
Stra
nded
iron
wir
es a
reso
met
imes
use
d, b
ut th
ere
are
seve
ral r
easo
ns w
hy a
con
duct
or o
f th
isde
scri
ptio
n sh
ould
be
avoi
ded.
With
the
sam
e re
sist
ance
as
aso
lidw
ire
a st
rand
ed c
ondu
ctor
has
fro
m 5
to 1
0 pe
r ce
nt. g
reat
er s
tatic
capa
city
than
a p
lain
wir
e.It
als
o af
ford
s a
larg
e an
d fa
vour
able
sur
face
for
the
depo
sit o
f sn
ow, a
nd, m
oreo
ver,
impu
ritie
s w
hich
impa
ir th
edu
rabi
lity
of th
e w
ire
beco
me
lodg
ed b
etw
een
the
stra
nds.
If th
e w
ires
of
the
loop
are
of
sim
ilar
dim
ensi
ons
and
mat
eria
l the
bala
nce
of th
e ci
rcui
t as
rega
rds
self
-ind
uctio
nis
assu
red.
Ele
ctro
-m
agne
ts s
houl
d be
avo
ided
in th
e ac
tual
line
cir
cuit,
and
sho
uld
be jo
ined
in "
bri
dge
" ac
ross
the
lines
.T
he r
easo
n fo
r th
is a
rran
gem
ent w
ill b
eex
plai
ned
late
r.
Whe
n th
e fo
rego
ing
cond
ition
s ha
ve b
een
fulf
illed
they
are
sta
ble,
but
the
insu
latio
n of
the
loop
is a
qua
ntity
whi
ch is
sub
ject
to c
ontin
ual
vari
atio
n.If
eac
h of
the
wir
es is
unif
orm
ly in
sula
ted,
and
the
tota
l
FIG
. 28.
insu
latio
n re
sist
ance
is th
e sa
me,
the
amou
nt o
f le
akag
e fr
om e
ach
wir
eis
iden
tical
.T
he in
sula
tion
resi
stan
ce w
ill b
e eq
uiva
lent
to a
fau
lt,te
rmed
the
resu
ltant
fau
lt, a
t the
cen
tre
of e
ach
line.
The
res
ista
nce
ofth
e re
sulta
nt f
ault
will
be
equa
l to
the
join
t res
ista
nce
of a
ll th
e pa
ths
ofle
akag
e.T
he b
alan
ce w
ill b
e th
us m
aint
aine
d, a
nd th
e ne
utra
l poi
nts
ofth
e ci
rcui
t will
rem
ain
at th
e en
ds (
Fig.
98)
.If
the
insu
latio
n of
one
wir
e be
mor
e pe
rfec
t tha
n th
at o
f th
e ot
her
ther
e w
ill b
e a
grea
ter
leak
age
f re
m th
e la
tter,
and
the
bala
nce
of th
e lo
op w
ill b
e up
set.
Con
side
ring
dyna
mic
indu
ctio
n, th
ere
will
be
a pr
epon
dera
nce
of in
duce
d cu
rren
tre
tain
ed b
y th
e m
ore
perf
ectly
insu
late
d w
ire,
and
com
plet
e ne
utra
lisat
ion
will
not
be
effe
cted
.T
he r
ecei
vers
will
con
sequ
ently
be
actu
ated
and
the
circ
uit w
ill b
e no
isy.
if th
e le
akag
e fr
om o
ne o
f th
e w
ires
be
not u
nifo
rmly
dis
trib
uted
, or
if a
spec
ific
fau
lt ex
ist,
the
posi
tion
of th
e re
sulta
nt f
ault
will
be
chan
ged.
By
them
alte
ring
the
poin
t of
disc
harg
e th
e ne
utra
l poi
nts
of th
e ci
rcui
t will
ho m
oved
and
indu
ced
curr
ents
will
pass
thro
ugh
the
rece
iver
s.
99.)
162
NO
TE
S O
N T
EL
EG
RA
PHY
.
CH
APT
ER
XX
I.
TH
E M
ET
AL
LIC
LO
OP.
Ver
y ea
rly
in th
e hi
stor
y of
tele
phon
y it
was
dis
cove
red
that
the
use
of a
sin
gle
-wir
e ci
rcui
t with
an
eart
h re
turn
was
not
pro
duct
ive
of g
ood
resu
lts.
A te
leph
one
rece
iver
is a
ver
y se
nsiti
ve in
stru
men
t, an
d is
con
-se
quen
tly a
ctua
ted
by v
ery
min
ute
curr
ents
or
slig
ht c
hang
es in
the
stre
ngth
of
a cu
rren
t.L
eaka
ge, e
arth
cur
rent
s, a
nd m
any
othe
r ca
uses
E4.
F.IG
. 9 2
.
tend
to p
rodu
ce w
hat i
s kn
own
as a
noi
sy c
ircu
it.T
he c
hief
fac
tor,
how
..ev
er, i
n pr
oduc
ing
a di
stur
banc
e of
this
kin
d is
indu
ctio
n.T
here
are
two
kind
s of
indu
ctio
n, v
iz.,
elec
tro-
stat
ic in
duct
ion
and
dyna
mic
, or
elec
tro-
mag
netic
indu
ctio
n.St
atic
indu
ctio
n ha
s al
read
y be
en d
ealt
with
at s
ome
leng
th in
con
nect
ion
with
the
theo
ry o
f th
e co
nden
ser.
It w
ill b
e re
mem
bere
d th
at a
cha
rged
4.
4-4
body
act
s in
duct
ivel
y up
on a
ll ne
ighb
ouri
ng c
ondu
ctor
s, in
duci
ng a
bou
ndch
arge
of
oppo
site
kin
d up
on th
e ne
ar s
ide
of th
em, a
nd r
epel
ling
a fr
eean
d si
mila
r ch
arge
to th
e fa
r si
de.
Con
side
r th
ese
effe
cts
in c
onne
ctio
nw
ith tw
o ad
jace
nt te
legr
aph
or te
leph
one
wir
esSu
ppos
e on
e to
bech
arge
d po
sitiv
ely
by a
n ea
rth
-con
nect
ed b
atte
ry, a
nd th
e ot
her
to b
ein
sula
ted
at e
ach
end
as in
dica
ted
in F
ig. 9
2.T
he s
econ
d w
ire
will
hav
ean
indu
ced
posi
tive
pote
ntia
l, an
d, if
the
circ
uit b
e ea
rthe
d at
eac
h en
dth
roug
h a
tele
phon
e re
ceiv
er (
Fig.
93)
ther
e w
ill b
e a
disc
harg
e of
pos
itive
NO
TE
S O
N T
EL
EG
RA
PHY
.16
9
elec
tric
ity in
the
form
of
a m
omen
tary
cur
rent
thro
ugh
each
inst
rum
ent.
As
soon
as
the
indu
cing
cha
rge
is r
emov
ed f
rom
the
firs
t wir
e cu
rren
tsfl
ow f
rom
the
eart
h to
the
seco
nd w
ire
and
prod
uce
a ne
utra
lisin
g ef
fect
upon
the
now
rel
ease
d ne
gativ
e ch
arge
.T
his
effe
ct is
sho
wn
in F
ig. 9
4.E
lect
ro-s
tatic
indu
ctio
n m
ay b
e su
mm
ed u
p by
say
ing
that
a c
harg
ed w
ire
prod
uces
a r
edis
trib
utio
n of
ele
ctri
fica
tion
in n
eigh
bour
ing
wir
es, a
nd if
the
latte
r fo
rm p
arts
of
clos
ed c
ircu
its c
urre
nts
of m
omen
tary
dur
atio
n
E
FIG
. 94
will
flo
w th
roug
h th
orn.
A w
ire
carr
ying
a c
urre
nt p
osse
sses
a s
tatic
char
ge b
y vi
rtue
ofits
elec
tro-
stat
icca
paci
ty, a
nd a
suc
cess
ion
ofcu
rren
ts in
a te
legr
aph
circ
uit i
nduc
e m
any
mom
enta
ry c
urre
nts
whi
chac
tuat
e th
e re
ceiv
ers
in n
eigh
bour
ing
tele
phon
e ci
rcui
ts.
Dyn
amic
or
elec
tro-
mag
netic
indu
ctio
n is
pro
duce
d by
ele
ctri
city
inm
otio
n.A
wir
e ca
rryi
ng a
cur
rent
is s
urro
unde
d by
a f
ield
o';.
.for
ce a
ndex
hibi
ts m
agne
tic p
rope
rtie
s as
long
as
the
curr
ent f
low
s.T
ile li
nes
offo
rce
of th
e m
agne
tic f
ield
rad
iate
in c
once
ntri
c ci
rcle
s fr
om th
e w
ire,
whi
ch is
thei
r co
mm
on c
entr
e.W
hen
the
curr
ent i
s st
arte
d th
e lin
es o
ffo
rce
may
be
said
to r
adia
te in
an
outw
ard
dire
ctio
n fr
om th
e w
ire,
and
if
.E,
- )E
FIG
95.
the
lines
of
forc
e cu
t thr
ough
an
adja
cent
con
duct
or, f
orm
ing
part
of
acl
osed
cir
cuit,
an
indu
ced
curr
ent w
ill b
e se
t up
in th
e la
tter.
An
incr
ease
in th
e st
reng
th o
f th
e pr
imar
y cu
rren
t will
cau
se a
fur
ther
rad
iatio
n of
the
lines
of
forc
e an
d a
sim
ilar
resu
lt w
ill e
nsue
.W
ith th
e ce
ssat
ion
of th
e pr
imar
y cu
rren
t the
line
s of
for
ce m
ay b
e as
sum
ed to
col
laps
e,or
rec
ede
into
the
wir
e.A
s th
ey w
ill n
ow c
ut th
roug
h an
adj
acen
tco
nduc
tor
inth
eop
posi
tedi
rect
ion
the
indu
ced
curr
ent
will
bere
vers
ed.
A d
ecre
ase
in th
e st
reng
th o
f th
e pr
imar
y cu
rren
t will
cau
se a
Li 2
170
NO
TE
S O
N T
EL
EG
RA
PHY
.
In th
e si
ngle
line
sys
tem
itis
adv
anta
geou
s to
join
up
inte
rmed
iate
appa
ratu
s in
" le
ak,"
and
whe
re th
e of
fice
is s
ome
dist
ance
fro
m th
e m
ain
rout
e th
e sa
ving
of
mat
eria
l is
a co
nsid
erat
ion.
If th
e ap
para
tus
at a
nin
term
edia
te s
tatio
n w
ere
join
ed in
" s
erie
s "
a fa
ult i
n it
wou
ld in
terr
upt
com
mun
icat
ion
betw
een
the
offi
ces
on e
ach
side
.T
his,
how
ever
, is
not s
ow
ith th
e le
ak s
yste
m, a
s w
ill b
e re
adily
see
n by
ref
eren
ce to
Fig
. 101
. The
obje
ctio
n to
a s
ingl
e lin
e, h
owev
er, i
s th
e ne
cess
ity f
or a
n ea
rth
retu
rn, t
hese
riou
s di
sadv
anta
ges
of w
hich
hav
e al
read
y be
en d
escr
ibed
.
TH
E P
ER
MA
NE
NT
CU
RR
EN
T S
YST
EM
.
Thi
s sy
stem
has
bee
n ge
nera
lly a
dopt
ed b
y th
e B
ritis
h Po
st O
ffic
e.A
t eac
h en
d of
a tr
unk
circ
uit t
wo
batte
ries
of
Lec
lanc
hb c
ells
are
empl
oyed
.O
ne is
cal
led
the
mai
n ba
ttery
,an
d pr
oduc
es th
e m
ain
perm
anen
t cur
rent
fro
m it
s si
x ce
lls, w
hils
t the
oth
er, c
onsi
stin
g of
thre
ece
lls, s
uppl
ies
a lo
cal p
erm
anen
t cur
rent
.A
pol
aris
ed in
dica
tor
rela
y,an
d th
e la
rger
bat
tery
are
in s
erie
s at
the
end
of th
e ci
rcui
t with
the
two
lines
, whi
le th
e sm
alle
r ba
ttery
isjo
ined
acr
oss
one
coil,
viz
., th
e ri
ght-
hand
coi
l, of
the
rela
y (F
ig. 1
02).
Bot
h m
ain
batte
ries
hav
e th
eir
posi
tive
A L
ee__
_ ._
___-
..-.-
3).
P C
---
--PC
-.J.
---1
-- .>L
ilo)
PC
I
Fic,
W2
pole
s co
nnec
ted
with
the
" A
" li
ne, a
nd th
e el
ectr
o-m
otiv
e fo
rces
bei
ngeq
ual a
nd o
ppos
ite te
nd to
set
up
oppo
sing
cur
rent
s w
hich
neu
tral
ise
each
othe
r. E
ach
loca
l bat
tery
, how
ever
, pro
duce
s a
defl
ectio
n of
the
indi
cato
rto
war
ds th
e ri
ght-
hand
sid
e.N
ow, w
hen
an o
pera
ting
peg
is in
sert
ed (
Fig.
103
) at
eith
er e
nd o
f th
eci
rcui
t the
loca
l pol
aris
ed in
dica
tor
rela
y an
d m
ain
batte
ry a
ro a
utom
atic
-al
ly c
ut o
ut.
Thi
s en
able
s th
e m
ain
batte
ry c
urre
nt f
rom
the
dist
ant
stat
ion
to f
low
thro
ugh
both
coi
ls o
f th
e in
dica
tor
rela
y at
that
sta
tion
and
an in
crea
sed
mag
netic
eff
ect i
s pr
oduc
ed.
The
mai
n cu
rren
t thr
ough
the
righ
t-ha
nd c
oil p
repo
nder
ates
and
is in
an
oppo
site
dir
ectio
n to
that
of
the
loca
l per
man
ent c
urre
nt ;
it ac
tuat
es th
e re
lay
acco
rdin
gly.
The
nee
dle
of th
e in
dica
tor
is th
us d
efle
cted
tow
ards
the
left
-han
d si
de a
nd a
cal
lsi
gnal
is p
rodu
ced.
A c
oil o
f 35
0 oh
ms
resi
stan
ce is
join
ed in
cir
cuit
with
NO
TE
S O
N T
EL
EG
RA
PHY
.17
1
the
loca
l bat
tery
at e
ach
end.
Thi
s pr
even
ts a
larg
e am
ount
of
the
mai
ncu
rren
t fro
m p
assi
ng th
roug
h th
e ot
herw
ise
com
para
tivel
y lo
w r
esis
tanc
e of
that
cir
cuit.
With
out s
uch
coil
it is
obv
ious
that
the
grea
ter
port
ion
ofth
e m
ain
curr
ent w
ould
not
pas
s th
roug
h th
e ri
ght-
hand
coi
l, an
d th
eef
fect
upo
n th
e in
dica
tor
rela
y w
ould
be
cons
ider
ably
dim
inis
hed.
The
adv
anta
ges
of th
e pe
rman
ent c
urre
nt s
yste
m a
re th
at a
ttent
ion
isga
ined
aut
omat
ical
ly a
nd a
" r
ing
off
" si
gnal
is p
rodu
ced
by th
e sa
me
mea
ns.
The
inse
rtio
n of
a p
eg in
to th
e sw
itch
spri
ngs
join
sup
the
oper
ator
's te
leph
one
and
the
" ri
ng o
ff "
app
arat
us in
bri
dge
acro
ss th
eco
rd, w
hich
ser
ves
as th
e co
nnec
tion
betw
een
two
circ
uits
.T
he p
erm
anen
t cur
rent
sys
tem
is a
lso
used
for
sub
scri
bers
' lin
es, a
nd in
this
cas
e th
e cu
rren
t is
from
the
subs
crib
er's
end
onl
y.T
he in
dica
tor
shut
ter
at th
e E
xcha
nge
is h
eld
mag
netic
ally
by
the
effe
cts
ofth
iscu
rren
t.T
he la
tter
is c
ut o
ff b
y th
e re
mov
al o
f th
e su
bscr
iber
's r
ecei
ver
AL
ine
13L
INE
..
FiG
.103
.
from
its
posi
tion
on th
e au
tom
atic
sw
itch
-lev
er.
A b
reak
dow
n of
the
line
is r
eadi
ly d
etec
ted,
as
atte
ntio
n is
dra
wn
to th
e ci
rcui
t by
the
failu
reof
the
curr
ent.
The
Exc
hang
e ga
ins
the
atte
ntio
n of
a s
ubsc
ribe
r by
augm
entin
g th
e st
reng
th o
f th
e pe
rman
ent c
urre
nt, w
hich
pas
ses
thro
ugh
a re
lay
at th
e su
bscr
iber
's o
ffic
e.T
his
rela
y re
spon
ds to
the
incr
ease
dcu
rren
t onl
y, a
nd is
not
act
uate
d by
the
ordi
nary
per
man
ent c
urre
nt.
TH
E T
RA
NSF
OR
ME
R.
Tra
nsfo
rmer
s or
tran
slat
ors
are
spec
ially
con
stru
cted
indu
ctio
n co
ils f
orus
e up
on s
uper
impo
sed
circ
uits
and
for
tran
slat
ing
the
curr
ents
fro
m a
sing
le li
ne to
a m
etal
lic lo
op c
ircu
it, a
nd v
ice
vers
a.T
he c
ore
com
pris
esa
bund
le o
f ve
ry s
oft i
ron
wir
es a
bout
dou
ble
the
leng
th o
f th
e co
ils.
The
prim
ary
and
seco
nds-
) co
ils a
re b
oth
of a
com
para
tivel
y hi
gh r
esis
tanc
ean
d th
e pr
opor
tion
ofth
e fo
rmer
to th
ela
tter
issm
all c
ompa
red
with
that
ofth
eor
dina
ryin
duct
ion
coil.
Apr
imar
yco
ilof
140
ohm
s an
da
seco
ndar
yco
ilof
290
ohm
s w
olln
dcl
osel
yan
d
172
NO
TE
S O
N T
EL
EG
RA
PHY
.
regu
larl
yin
alte
rnat
ela
yers
prod
uce
satis
fact
ory
resu
lts.
The
obje
ct f
or w
indi
ng th
e co
ils to
a c
ompa
rativ
ely
high
res
ista
nce
is th
atea
ch m
ust a
ct a
s pr
imar
y or
sec
onda
ry c
oil i
n tu
rn, a
ccor
ding
as
the
spea
king
is in
one
dir
ectio
n or
the
othe
r.T
he a
ltern
ate
met
hod
of w
ind-
ing
is to
pro
duce
an
equa
lity
of m
agne
tic e
ffec
ts in
bot
h co
ils.
The
prot
rudi
ng e
nds
of th
e w
ire
form
ing
the
core
are
spr
ead
out a
nd d
oubl
edba
ck o
ver
the
coils
and
mad
e to
ove
rlap
.A
com
plet
e m
agne
tic c
ircu
it is
thus
for
med
, and
the
indu
ctiv
e ef
fect
is in
crea
sed
by th
e w
ire
actin
g as
a
sinG
a L
omL
oOP.
°AZ
flG
, 104
.
shea
th w
hich
con
cent
rate
s th
e lin
es o
f fo
rce
thro
ugh
the
coils
.A
tran
s-fo
rmer
is u
sed
to e
ffec
t a ju
nctio
n be
twee
n a
sing
le w
ire
and
a m
etal
liclo
op, a
nd th
e hi
gher
res
ista
nce
coil
is jo
ined
to th
e lo
op c
ircu
it, w
hich
isge
nera
lly o
f a
rela
tivel
y hi
gh r
esis
tanc
e.T
he a
rran
gem
ent i
ssh
own
theo
retic
ally
in F
ig. 1
04, a
nd it
will
be
read
ily u
nder
stoo
d th
at th
e ad
van-
tage
s of
the
loop
are
ret
aine
d.T
he n
umbe
r of
tran
sfor
mer
s is
nec
essa
rily
rest
rict
ed in
for
min
g co
nnec
tions
of
this
des
crip
tion,
how
ever
, as
each
one
in a
cir
cuit
enta
ils a
loss
of
ener
gy.
to- P5.
1A -
P. 0
-S.
SU P
ER
I*, r
*S41
D
FIG
. 105
.
TH
E S
UPE
RIM
POSE
D C
IRC
UIT
.
N°2
Whe
n tw
o ci
rcui
ts c
onne
ct tw
o of
fice
s a
thir
d ci
rcui
t may
be
wor
ked
bym
eans
of
supe
rim
posi
ng.
In th
e Po
st O
ffic
e su
peri
mpo
sed
wor
king
isef
fect
ed b
y th
e us
eof
tran
sfor
mer
s.T
he a
rran
gem
ent
issh
own
diag
ram
atic
ally
in F
ig. 1
05.
At b
oth
ends
of
the
circ
uits
the
switc
h -
spri
ngs
of e
ach
circ
uit a
re c
onne
cted
to th
e pr
imar
y co
ils o
f tr
ansf
orm
ers.
The
sec
onda
ry c
oils
are
div
ided
into
two
equa
l sec
tions
, the
sw
itch
-spr
ings
of th
e su
peri
mpo
sed
circ
uit b
eing
con
nect
ed to
the
junc
tions
of
the
sect
ions
as in
dica
ted.
NO
TE
S O
N T
EL
EG
RA
PHY
.17
3
The
two
loop
s ut
ilise
d fo
r su
peri
mpo
sing
sho
uld
have
the
sam
e co
n-du
ctor
res
ista
nce,
insu
latio
n re
sist
ance
and
cap
acity
.In
fac
t, th
ey s
houl
dbe
sim
ilar
in a
ll re
spec
ts.
Furt
her,
the
four
wir
es s
houl
d fo
rm th
edi
agon
als
of a
squ
are
upon
the
pole
s an
d be
sym
met
rica
lly r
evol
ved.
One
loop
ser
ves
the
purp
ose
of th
e "
A "
line
and
the
othe
r th
at o
f th
e "
B "
line
of th
e su
peri
mpo
sed
or +
1 c
ircu
it.T
he tw
o m
ain
circ
uits
are
wor
ked
thro
ugh
tran
sfor
mer
s.T
he c
urre
nts
trav
ersi
ng th
e pr
imar
y co
ilfr
om th
e tr
ansm
itter
indu
ce s
imila
r cu
rren
ts in
the
seco
ndar
y co
il an
dpa
ss to
the
line.
The
indu
ced
curr
ents
cir
cula
te th
roug
h th
e se
cond
ary
coil
at th
e di
stan
t off
ice
and,
by
indu
ctio
n, s
imila
r cu
rren
ts p
ass
thro
ugh
the
prim
ary
coil,
and
then
ce th
roug
h th
e sw
itch
spri
ngs
to th
e re
ceiv
er.
The
effe
ct u
pon
the
supe
rim
pose
d ci
rcui
t, ho
wev
er. w
ill b
e ni
l, as
the
cent
re o
r
LIN
E
FIG
. 106
.
junc
tion
of th
e tw
o se
ctio
ns o
f th
e se
cond
ary
coil
will
be
at z
ero
pote
ntia
l.C
urre
nts
from
the
appa
ratu
s us
ed f
or th
e su
peri
mpo
sed
circ
uits
, how
ever
,w
ill d
ivid
e at
the
junc
tion,
and
, aft
er tr
aver
sing
the
" A
." a
nd "
B "
line
s,w
ill r
euni
te a
t the
cen
tre
of th
e co
rres
pond
ing
tran
sfor
mer
at t
he d
ista
ntst
atio
n an
d pa
ss th
roug
h th
e su
peri
mpo
sed
appa
ratu
s at
that
off
ice.
The
retu
rn c
ircu
it w
ill b
e yi
d th
e se
cond
ary
coils
and
the
" A
" a
nd "
B "
line
sof
the
seco
nd c
ircu
it th
roug
h w
hich
the
curr
ents
will
aga
in s
plit
and
re -
com
bine
as
befo
re.
The
app
arat
us c
onne
cted
with
the
two
mai
nci
rcui
ts, h
owev
er, w
ill n
ot b
e ac
tuat
ed, a
s in
eac
h of
the
four
tran
sfor
mer
sth
ecu
rren
ts in
duce
din
the
prim
ary
coil,
by
the
divi
ded
curr
ents
trav
ersi
ng th
e tw
o se
ctio
ns o
f ea
ch s
econ
dary
coi
l,w
ill b
e ne
utra
lised
,be
ing
equa
l and
in o
ppos
ite d
irec
tions
.Su
peri
mpo
sed
wor
king
ren
ders
the
aban
donm
ent o
f pe
rman
ent c
urre
ntw
orki
ng n
eces
sary
on
the
two
mai
n ci
rcui
ts, a
nd r
ingi
ng u
pon
thes
e ci
r-cu
its is
eff
ecte
d by
mea
ns o
f al
tern
atin
g cu
rren
ts, a
non
-po
lari
sed
indi
cato
rre
lay
bein
g us
ed.
By
a si
mpl
e re
-ar
rang
emen
t at t
he te
st -
box
supe
rim
pose
d w
orki
ng m
aybe
rea
dily
dis
pens
ed w
ith, a
nd o
rdin
ary
wor
king
res
tore
d up
on th
e tw
om
ain
circ
uits
.
174
NO
TE
S O
N T
EL
EG
RA
PHY
.
Supe
rim
posi
ng h
as a
gre
at d
isad
vant
age
from
a tr
affi
c po
int o
f vi
ew, a
sth
e br
eakd
own
of o
ne lo
op r
educ
es th
e av
aila
ble
outle
ts f
rom
thre
e to
one
,an
d co
nges
tion
inev
itabl
y re
sults
.T
his
syst
em, h
owev
er, s
aves
the
cost
of e
rect
ion
and
mai
nten
ance
of
a th
ird
loop
.U
nder
goo
d co
nditi
ons
itw
orks
sat
isfa
ctor
ily, a
nd is
bei
ng la
rgel
y ad
opte
d in
the
Post
Off
ice.
SIM
UL
TA
NE
OU
S T
EL
EG
R &
PRY
AN
D T
EL
EPH
ON
Y.
The
Van
Rys
selb
ergh
e sy
stem
of
com
bine
d te
legr
aphy
and
tele
phon
y is
one
of m
any
syst
ems
for
effe
ctin
g te
legr
aphi
c an
d te
leph
onic
com
mun
ica-
tion
upon
the
sam
e ci
rcui
t.T
he s
peed
of
wor
king
the
tele
grap
h po
rtio
nof
the
appa
ratu
s, o
f ne
cess
ity, m
ust b
e lim
ited.
The
ris
e an
d fa
ll of
the
tele
grap
h cu
rren
ts a
re r
ende
red
com
para
tivel
y sl
ow b
y th
e in
trod
uctio
n of
reta
rdat
ion
coils
whi
ch p
osse
ss g
reat
ele
ctro
-mag
netic
iner
tia, a
nd c
on-
dens
ers.
Tel
epho
ne r
ecei
vers
bei
ng a
ctua
ted
by r
apid
ly v
aryi
ng c
urre
nts,
or c
urre
nts
of a
pul
satin
g na
ture
, are
pra
ctic
ally
unaf
fect
ed b
y th
ere
tard
ed c
urre
nts
used
for
the
tele
grap
h sy
stem
.U
pon
the
othe
r ha
nd, -4 1.
4 r- rq p As) X.
FIG
107
1
the
tele
grap
h ap
para
tus
isno
t act
uate
d by
the
min
ute
and
ever
-ch
angi
ng c
urre
nts
whi
ch a
re in
disp
ensa
ble
for
effe
ctiv
e te
leph
ony.
The
tele
phon
e ci
rcui
t is
wor
ked
thro
ugh
a co
nden
ser
of h
alf
a m
icro
-fa
rad
capa
city
, and
the
rece
iver
is a
ctua
ted
by th
e co
nden
ser
impu
lses
.T
his
cond
ense
r al
so b
reak
s th
e co
ntin
uity
of
the
circ
uit i
n th
e te
leph
one
sect
ion
of th
e ap
para
tus,
and
the
reta
rded
tele
grap
h cu
rren
ts c
onse
quen
tlytr
aver
se th
e lin
e.A
theo
retic
al d
iagr
am is
sho
wn
in F
ig. 1
06.
A te
legr
aph
circ
uit m
ay b
e w
orke
d up
on a
met
allic
loop
by
join
ing
itsap
para
tus
in b
ridg
e.A
bet
ter
syst
em o
fsi
mul
tane
ous
wor
king
isef
fect
edby
sup
erim
-po
sing
ate
legr
aph
circ
uit
upon
am
etal
liclo
op b
y m
eans
of
tran
sfor
mer
s.T
he a
rran
gem
ent i
s sh
own
in F
ig. 1
07.
The
cur
rent
s fr
omth
e te
legr
aph
batte
ry d
ivid
e eq
ually
thro
ugh
the
seco
ndar
y co
il an
d,af
ter
trav
ersi
ng th
e w
ires
of
the
loop
, re
-com
bine
at t
he c
orre
spon
ding
junc
tion
at th
e di
stan
t sta
tion
and
pass
to e
arth
thro
ugh
the
tele
grap
hap
para
tus.
The
cur
rent
s in
duce
d in
the
prim
ary
coils
are
equ
al in
str
engt
h
NO
TE
S O
N T
EL
EG
RA
PHY
.17
6
and
oppo
site
in d
irec
tion
and
the
tele
phon
e ap
para
tus
is c
onse
quen
tly n
otac
tuat
ed.
Tel
epho
nic
com
mun
icat
ion
isef
fect
edby
indu
ctio
nbe
twee
n th
e pr
imar
y an
d se
cond
ary
coils
of
the
tran
sfor
mer
s.T
he
indu
ced
curr
i,n;)
atr
aver
se th
e se
ctio
ns o
f th
ese
cond
ary
coil
at th
e"
spea
king
" o
ffic
e an
d pa
ss th
roug
h th
e w
hole
coi
l fro
m e
nd to
end
,ac
ting
in s
ynch
roni
sm w
ith th
ose
in th
e pr
imar
y ci
rcui
t.A
fter
flo
win
gal
ong
the
loop
they
indu
ce s
imila
r cu
rren
ts in
the
prim
ary
coil
at th
ere
ceiv
ing
end,
and
the
rece
iver
is c
onse
quen
tly a
ctua
ted.
168
NO
TE
S O
N T
EL
EG
RA
PHY
.
It s
houl
d be
em
phas
ised
, per
haps
, tha
t by
cons
truc
ting
a ba
lanc
edci
rcui
t ind
uctio
n is
not
obv
iate
d, b
ut it
s ef
fect
s ar
e m
erel
y ov
erco
me.
Itsh
ould
als
o be
poi
nted
out
that
not
onl
y is
the
revo
lvin
g or
twis
ting
of th
ew
ires
car
ried
out
on
aeri
al li
nes,
but
the
sam
e co
nditi
ons
exis
t in
cabl
esan
d co
vere
d w
ires
.
Thi
s sy
stem
of
revo
lvin
g is
car
ried
out
alo
ng th
e en
tire
leng
th o
f al
l
ikc
FIG
:
tele
phon
e ci
rcui
ts ;
som
etim
es th
e pa
irs
of a
loop
are
twis
ted,
but
mor
e fr
e-qu
ently
the
wir
es f
orm
ing
two
dist
inct
cir
cuits
are
uni
form
ly r
evol
ved
toef
fect
a b
alan
ce.
Ano
ther
adv
anta
ge o
f th
e lo
op is
that
a c
urre
nt p
assi
ng a
long
one
wir
ein
duce
s a
curr
ent i
n th
e ot
her
wir
e.T
he in
duce
d cu
rren
t flo
ws
in th
esa
me
dire
ctio
n as
the
prim
ary
curr
ent a
long
the
seco
nd w
ire
of th
e lo
op,
and
the
mut
ual i
nduc
tion
is b
enef
icia
l to
the
wor
king
of
the
circ
uit.
NO
TE
S O
N T
EL
EG
RA
PHY
.16
9
CH
APT
ER
XX
II.
ME
TH
OD
S O
P W
OR
KIN
G.
Inte
rmed
iate
Stat
ions
.-T
here
are
thre
e m
etho
dsof
join
ing
upin
term
edia
te a
ppar
atus
upon
met
allic
loop
s ;
(a)
" or
dina
ry "
or
" se
ries
,"(b
) "
diff
eren
tial,"
(c)
" b
ridg
e."
The
fir
st in
trod
uces
dif
ficu
lties
thro
ugh
the
bala
nce
of th
eci
rcui
t bei
ngdi
stur
bed,
and
the
ill-e
ffec
ts o
f in
duct
ion
resu
lt.T
he o
bjec
tion
to th
e
FiG
100
.
diff
eren
tial m
etho
d is
in th
ene
cess
ary
doub
le w
indi
ng o
f th
e in
duct
ion
and
rece
iver
coi
ls.
The
re a
re b
oth
mec
hani
cal a
nd e
lect
rica
l dis
adva
ntag
esin
dou
ble
win
ding
the
appa
ratu
s, b
ut f
rom
a te
leph
onic
poi
nt o
f vi
ew th
ism
etho
d is
fai
rly
good
.T
he "
bri
dge
" m
etho
d is
pre
-em
inen
tly s
uper
ior
to th
e ot
her
two.
As
man
y as
ten
stat
ions
may
be
in c
ircu
itup
on th
esa
me
loop
whe
n th
e in
stru
men
ts a
re in
" b
ridg
e,"
as th
e ch
okin
g ef
fect
of
SER
IES.
LE
R I
(
F1Q
101
.
the
inte
rmed
iate
app
arat
us...
4u°
to th
eel
ectr
o-m
agne
tic in
ertia
or
self
-In
duct
ion
of th
eco
ils,
serv
es a
use
ful p
urpo
se.
The
inte
rmed
iate
appa
ratu
s w
ill b
e ac
tuat
ed b
y a
part
of
the
curr
ent,
but t
he r
emai
nder
will
bo
chok
ed o
ut, a
nd c
ause
d to
pass
to d
ista
nt s
tatio
ns.
Furt
her,
afa
ult i
n th
e ap
para
tus,
oth
er th
an th
at o
f sh
ort-
circ
uit,
will
not
bre
akdo
wn
com
mun
icat
ion
with
oth
er o
ffic
es, a
nd .t
he to
tal r
esis
tanc
e fr
oman
y ri
ngin
g po
int w
ill b
o de
crea
sed.
The
" b
ridg
e "
syst
em is
sho
wn
dlag
rain
atic
ally
in F
ig. 1
00.
176
NO
TE
S O
N T
EL
EG
RA
PHY
.
CH
APT
ER
XX
III.
TH
E K
R L
AW
.
Sir
Will
iam
Tho
mso
n, n
ow L
ord
Kel
vin,
est
ablis
hed
this
law
aft
erin
vest
igat
ing
the
effe
ct th
at r
esis
tanc
e an
d ca
paci
ty o
f a
cabl
e ha
ve u
pon
the
rise
and
fal
l of
elec
tric
cur
rent
s.Fo
r th
e pr
actic
al p
urpo
seof
asce
rtai
ning
the
dim
ensi
ons
of c
able
s to
ens
ure
a gi
ven
spee
d th
e qu
estio
nof
the
tota
l im
peda
nce
of th
e ci
rcui
ts h
ad to
be
settl
ed.
The
" ti
me
cons
tant
" o
f a
circ
uit i
s th
e tim
e th
at a
cur
rent
take
s to
ris
e fr
om z
ero
toits
max
imum
str
engt
h an
d fa
ll ag
ain
to z
ero.
Om
ittin
g th
e po
int o
fel
ectr
o-m
agne
ticin
ertia
, whi
ch is
abs
ent i
n co
pper
con
duct
ors,
the
impe
danc
e to
the
rise
and
fal
l of
the
curr
ent i
s di
rect
ly p
ropo
rtio
nal t
o th
eca
paci
ty, K
, mul
tiplie
d by
the
resi
stan
ce R
-hen
ce th
e K
R la
w.
For
high
spe
ed te
legr
aphi
c pu
rpos
es th
e tim
e co
nsta
nt m
ust n
ot e
xcee
duh
of
a se
cond
, whe
reas
in te
leph
ony,
in w
hich
the
ever
-va
ryin
g cu
rren
tsri
ae a
nd f
all w
ith g
reat
rap
idity
, art
icul
ate
spee
ch is
not
ens
ured
if it
exce
eds
.6.0
10-0
- of
a s
econ
d.Fr
om th
is, t
hen,
it w
ill b
e se
en th
at th
e to
tal
impe
danc
e of
the
circ
uit w
hich
con
trol
s th
e ri
se a
nd f
all o
f th
e cu
rren
tssh
ould
be
kept
at a
min
imum
, in
orde
r th
at d
isto
rtio
n of
spe
ech
may
be
prev
ente
d.
The
lim
iting
KR
val
ues
to w
hich
spe
ech
has
been
asc
erta
ined
to b
epo
ssib
le h
ave
been
fou
nd e
xper
imen
tally
to b
e as
fol
low
s :
Cop
per
(ope
n),
15,0
00 ;
copp
er (
cove
red)
, 12,
000;
iron
, 10,
000.
The
se f
igur
es w
ere
arri
ved
at b
y m
ultip
lyin
g th
e ca
paci
ty in
mic
ro -
fara
ds b
y th
e re
sist
ance
in o
hms.
The
low
val
ue f
or ir
on is
due
to th
e el
ectr
o-m
agne
tic in
ertia
of
that
sub
-st
ance
, and
the
form
ula
is m
ore
com
plet
ely
stat
ed a
s :-
/K
R -
I-11
,
- ,n
who
re /
repr
esen
ts th
e el
ectr
o-m
agne
tic in
ertia
of
the
cond
ucto
r.
The
lim
iting
dis
tanc
e m
ay b
e ap
prox
imat
ely
calc
ulat
ed f
rom
form
ula
:-1
=A kr
in w
hich
1 =
the
leng
th o
f th
e ci
rcui
t in
mile
s.k
= th
e ca
paci
ty p
er m
ile.
r =
the
resi
stan
ce p
er m
ile.
A =
the
valu
e de
term
inin
g th
e lim
iting
dis
tanc
e.
the
NO
TE
S O
N T
EL
EG
RA
PHY
.17
7
The
tota
l cap
acity
of
the
circ
uit
= k
l. r
esis
tanc
e=
rl.
ar.d
the
KR
If=
kl x
rl =
kr1
2A
= k
r 12
1-=
A kr
and
1 =
A
A c
ompa
riso
n of
the
wor
king
spe
ed o
f a
met
allic
loop
and
a s
ingl
ew
ire
circ
uit i
s fr
eque
ntly
mad
e. A
met
allic
loop
is a
nala
gous
to tw
oco
nden
sers
join
ed in
" c
asca
de,"
and
its
capa
city
is c
onse
quen
tlyon
ly h
alf
that
of
a si
ngle
wir
e ci
rcui
t bet
wee
n th
e sa
me
poin
ts.
The
res
ista
nce
ofth
e m
etal
lic lo
op, h
owev
er, i
s do
uble
that
of
the
sing
le w
ire,
and
the
KR
of
the
circ
uits
is th
eref
ore
the
sam
e.
180
NO
TE
S O
N T
EL
EG
RA
PHS%
circ
uit i
s co
mpl
eted
thro
ugh
a on
e-am
pAre
fus
e fi
tted
in th
e ch
ambe
r.T
wo
hole
s w
hich
run
into
the
insu
lato
r al
low
con
nect
ing
wir
es to
be
carr
ied
from
the
fuse
to th
e tw
o se
ctio
ns o
f th
e lin
e.W
here
dam
age
from
con
tact
with
pow
er c
ircu
its is
ant
icip
ated
this
insu
lato
r is
of
grea
tse
rvic
e, a
s ap
para
tus
and
the
insu
latin
g m
ater
ial o
f un
derg
roun
d se
ctio
nsar
e pr
eser
ved
from
har
m b
y th
e fu
se d
isco
nnec
ting
the
circ
uits
.D
iffi
-cu
lty, h
owev
er, i
s so
met
imes
exp
erie
nced
fro
m th
e br
eakd
own
of th
eci
rcui
t, du
e to
hea
vy li
ghtn
ing
disc
harg
es p
assi
ng th
roug
h th
e fu
se.
Ext
ra s
tron
g in
sula
tors
are
fix
ed a
nd s
teel
spi
ndle
s us
ed u
pon
term
inal
pole
s w
hore
the
stre
ss is
abn
orm
al.
A w
ire
is f
requ
ently
run
alo
ng th
e to
p of
a p
ole,
and
a "
sad
dle
" st
ay,
in th
e fo
rm o
f a
galv
anis
ed ir
on b
and,
is a
ttach
ed to
an
ordi
nary
sad
dle
FIG
, 108
.
brac
ket.
Thi
s ar
rang
emen
t, to
geth
er w
ith tw
o bl
ocks
of
woo
d, o
ne u
pon
each
sid
e of
the
pole
, add
s st
reng
th to
the
insu
lato
r su
ppor
t.
In e
rect
ing
pole
s al
ong
road
and
rai
lway
rou
tes
the
aim
is to
so
arra
nge
them
that
the
prev
ailin
g ga
les
may
blo
w a
ny f
allin
g w
ires
or
the
pole
s th
em-
selv
es a
way
fro
m th
e tr
affi
c.A
s an
ext
ra p
reca
utio
n a
shor
t wir
e is
som
e-tim
es f
itted
upo
n th
e ar
m o
n th
e tr
affi
c si
de o
f a
pole
, and
ben
ds o
ver
the
insu
lato
r, f
orm
ing
a ho
ok.
A w
ire
beco
min
g de
tach
ed f
rom
the
insu
lato
ran
d fa
lling
upo
n th
is s
ide
wou
ld b
e in
terc
epte
d be
fore
rea
chin
g th
epa
ssin
g tr
affi
c.Ir
on s
hiel
ds a
re s
omet
imes
pla
ced
over
insu
lato
rs a
s a
prot
ectio
n ag
ains
t wilf
ul d
amag
e,T
hose
, how
ever
, sho
uld
neve
r be
NO
TE
S O
N T
EL
EG
RA
PHY
.18
1
empl
oyed
alo
ng a
sea
-co
ast r
oute
, if
exce
ptio
nal c
ircu
mst
ance
sde
man
dsu
ch a
rou
te b
eing
sel
ecte
d.T
he s
alt f
rom
the
atm
osph
ere
and
spra
yw
ould
acc
umul
ate
upon
the
insu
lato
rs, a
nd r
educ
eth
eir
effi
cien
cy;
but w
hen
unpr
otec
ted
they
are
kep
t cle
an b
y ra
in -
stor
ms.
SUPP
OR
TS.
Woo
den
pole
s ar
e ge
nera
lly u
sed
as th
e su
ppor
ts, a
nd, i
f th
orou
ghly
pres
erve
dbe
fore
erec
tion,
they
are
very
dura
ble.
Iron
pole
sar
eem
ploy
ed w
here
an
artis
tic e
ffec
t is
an o
bjec
t, bu
t a d
isad
vant
age
of ir
onis
that
a d
ispl
aced
wir
e in
con
tact
with
it w
ould
be
put t
o "
full
eart
h."
Iron
pol
es a
re m
ade
in s
ectio
ns a
nd a
re p
orta
ble
in c
onse
quen
ce, b
ut th
eir
initi
al c
ost i
s re
lativ
ely
grea
t.T
he w
oode
n po
les
are
in tw
o sh
apes
, " r
ound
" a
nd "
squ
are,
" an
dth
eir
size
s va
ry w
ith th
e w
eigh
t of
the
wir
es th
ey h
ave
to c
arry
, and
the
stre
ss to
whi
ch th
ey m
ay b
e su
bjec
ted
at c
erta
in p
oint
s en
rou
te.
All
" te
rmin
al "
pol
es a
re e
xtra
larg
e, a
nd th
ey a
re u
sual
ly o
f th
e "
squa
re "
patte
rn.
Ter
min
al p
oles
are
ere
cted
bot
h at
the
ends
of
a se
ctio
n an
dal
so w
here
the
wir
es f
orm
ang
les
appr
oxim
atin
g to
90d
eg.
The
" r
ound
"po
les
are
the
rod
fir
tree
s of
Nor
way
and
Sw
eden
spe
cial
ly s
elec
ted
and
" pr
eser
ved.
"W
ith f
ew e
xcep
tions
the
chos
en tr
ees
are
felle
d in
win
ter.
The
ir b
ark
is s
trip
ped
off,
and
they
are
then
sta
cked
in s
heds
whe
re a
fre
e ci
rcul
atio
nof
air
gen
eral
ly d
ries
up
the
sap.
The
y ar
e so
met
imes
cha
rred
at t
heir
low
er e
nds
to d
estr
oy v
eget
able
and
ani
mal
life
and
to c
lose
the
pore
sag
ains
t the
ingr
ess
of m
oist
ure.
A m
ixtu
re o
fta
r an
d lim
e, c
alle
d"
Stoc
khol
m "
tar,
is a
pplie
d to
the
butt
end,
and
this
pre
vent
s ra
pid
deca
y.It
is a
t the
gro
und
line
that
sig
ns o
f de
teri
orat
ion
usua
lly f
irst
appe
ar, t
here
fore
this
trea
tmen
t sho
uld
beex
tend
ed a
few
fee
t abo
ve th
egr
ound
line
.T
he u
pper
end
s of
the
pole
s ar
e th
en p
aint
ed; t
his
is th
eex
tern
al, t
reat
men
t for
pre
serv
atio
n.T
erm
inal
pol
es a
t the
end
s of
a li
near
e al
l tre
ated
in th
is w
ay b
ecau
se th
e po
pula
r m
etho
d of
" cr
eoso
ting
" is
unsu
itabl
e.L
eadi
ng -
in w
ires
at s
uch
pole
s ar
e in
dia-
rubb
er o
r gu
tta-
perc
ha c
over
ed, a
nd c
reos
ote
tend
s to
des
troy
thos
e m
ater
ials
.T
he in
tern
al p
roce
ss o
f pr
eser
vatio
n is
the
inje
ctio
n of
met
allic
sal
ts in
toth
e po
res
of th
e po
les,
and
thes
e sa
lts a
id in
pre
vent
ing
prem
atur
e de
cay.
Bur
netis
ing
and
Kya
nisi
ng e
ach
cons
ists
of
a sy
stem
atic
soa
king
of
the
pole
s, w
hen
wel
l sea
sone
d, in
a ta
nk c
onta
inin
g ch
lori
de o
f zi
ncin
the
form
er, a
nd p
erch
lori
de o
f m
ercu
ry in
the
latte
r ca
se.
Bou
cher
isin
g is
don
e w
hen
the
tree
s ar
e ne
wly
-fe
lled.
The
spr
ing
orau
tum
n is
a g
ood
time
of th
e ye
ar f
or th
is tr
eatm
ent,
whi
le th
e va
scul
arsy
stem
s of
the
tree
s ar
e op
en.
The
pol
es r
eadi
ly a
bsor
b a
solu
tion
ofco
pper
sul
phat
e an
d be
com
e im
preg
nate
dw
ith it
. The
re is
a s
erio
us o
bjec
-tio
n to
bou
cher
isin
g, h
owev
er, a
s th
e su
lpha
te o
f co
pper
has
a d
elet
erio
us
182
NO
TE
S O
N T
EL
EG
RA
PHY
.
effe
ct u
pon
the
bolts
and
sta
ples
use
d fo
rse
curi
ng th
e ar
ms,
etc
., to
the
pole
s, b
y ac
ting
chem
ical
ly u
pon
them
.
Cre
osot
ing
is p
erfo
rmed
whe
n th
e tr
ees
are
perf
ectly
sea
sone
d.T
his
met
hod
ofpr
eser
vatio
nis
in g
ener
al u
se, a
s its
eff
ects
are
end
urin
g.C
reos
ote
is a
n oi
ly s
ubst
ance
; it p
reve
nts
the
ingr
ess
of m
oist
ure
and
dest
roys
veg
etal
and
ani
mal
life
.C
reos
otin
g is
don
e in
a ta
nk e
xhau
sted
of
air,
and
the
liqui
d is
for
ced
into
the
woo
den
pole
s in
quan
titie
s of
101
bs. t
o12
1bs.
per
cub
ic f
oot.
The
chi
ef d
raw
-ba
ck to
cre
osot
e is
its
ill-e
ffec
ts u
pon
gutta
-per
cha
and
indi
a-ru
bber
.
.Pol
e-se
tting
.-T
he p
ositi
ons
the
pole
s ar
e to
occu
py a
re f
irst
mar
ked
out,
and
the
hole
s ar
e th
en d
ug w
ithou
t rem
ovin
g m
ore
eart
h th
an is
real
ly n
eedf
ul.
Roa
ds, e
tc.,
shou
ld n
ot b
e cr
osse
d un
nece
ssar
ily, a
nd th
ein
side
of
curv
es m
ust b
e in
vari
ably
take
n.E
ach
hole
is d
ug to
a d
epth
of
from
4ft
. to
6ft.,
the
deep
est p
art b
eing
rea
ched
by a
ste
p -l
ike
arra
nge-
men
t.A
rec
tang
ular
sur
face
is m
arke
dou
t, an
d th
e ho
le is
gra
dual
lyde
crea
sed
in s
ize
until
the
prop
er d
epth
has
bee
n m
ade.
The
se e
xcav
a-tio
ns a
re u
sual
ly m
ade
with
ord
inar
yto
ols,
but
in e
asily
wor
ked
soils
" bo
rers
" a
re e
mpl
oyed
whi
ch d
rill
circ
ular
hol
es ju
st la
rge
enou
gh to
rece
ive
the
pole
s, a
nd a
min
imum
am
ount
of
eart
h is
dist
urbe
d.T
here
ctan
gula
r ex
cava
tion
is u
sual
ly n
eces
sary
, how
ever
, and
its
leng
th is
alw
ays
para
llel w
ith th
e w
ires
.T
his
prev
ents
loos
enin
g of
the
eart
h at
the
two
fide
s of
the
pole
whe
re th
e te
nden
cy to
dra
wit
from
a p
erpe
ndi-
cula
r po
sitio
n ex
ists
.A
t the
sid
es o
f th
e ho
le, w
hich
are
par
alle
l with
the
wir
es, t
he e
arth
nea
r th
e po
le r
emai
ns f
irm
and
und
istu
rbed
.T
he b
urie
dpo
rtio
n of
the
pole
sho
uld
be a
bout
one
-fi
fth
of th
e to
tal
leng
th, a
nd 2
5po
les
to th
e m
ile a
re o
rdin
arily
em
ploy
ed.
The
pun
ner
shou
ld b
e us
edfr
eely
in f
illin
g in
the
hole
s to
mak
e th
e ea
rth
firm
and
prev
ent t
he p
oles
from
can
ting
over
aft
er s
ettin
g.L
ight
pol
es c
arry
one
to f
ive
wir
es,
med
ium
six
to te
n, s
tout
pol
es a
bove
ten;
the
latte
r are
als
o us
ed a
t sha
rpan
gles
.
Stru
ts a
nd S
tays
are
use
d re
spec
tivel
y to
cou
nter
act t
hepr
essu
re a
ndte
nsio
n of
for
ces
actin
g up
on th
e po
les.
In m
any
inst
ance
s, h
owev
er, t
hest
ruts
are
arr
ange
d to
cou
nter
act t
he e
ffec
ts o
f bo
th f
orce
s.O
n he
avy
wor
k, if
neith
erst
rut n
or s
tay
can
be u
sed,
two
pole
s ar
e sc
arf
-jo
inte
d at
thei
r to
ps a
nd b
olte
d fi
rmly
toge
ther
, the
ir b
ases
bein
g fi
xed
abou
t 2ft
. apa
rt.
At a
dis
tanc
e of
abo
ut 1
8in.
fro
m th
e bo
ttom
a pi
ece
Of
" pr
eser
ved
" tim
ber
is f
itted
acr
oss
the
pole
s an
d se
cure
d to
eac
h by
mea
ns o
f a
bolt.
Thi
s un
derg
roun
d ar
rang
emen
tpr
even
ts o
ne p
ole
from
liftin
g th
e ot
her
out o
f th
e ea
rth.
A f
ew f
eet a
bove
the
grou
nd a
n ir
ontie
-ro
dco
nnec
tsth
etw
opo
les.
Such
asu
ppor
tas
this
isca
lled
an "
A "
pol
e.W
here
the
wor
k is
exc
eedi
ngly
hea
vy, i
.e.,
whe
rea
very
larg
e nu
mbe
r of
wir
es is
nec
essi
tate
d up
on o
ne s
uppo
rt, o
r at
poi
nts
whe
re m
any
wir
es c
onve
rge,
Ein
d fo
rte
leph
one
wir
es th
e "
Z3,
" p
ole
NO
DE
S of
TE
LE
GR
AM
/V.
199
erec
ted.
In th
isca
se tw
o pa
ralle
l pol
es a
re s
et a
bout
3ft.
apar
tan
d bo
lted
toge
ther
at c
erta
in d
ista
nces
with
tie
-rod
s.T
he o
ppos
itean
gles
of
the
inte
rspa
ces
are
also
con
nect
ed w
ith ir
on r
ods
and
a la
ttice
FIG
. 109
.FI
G, l
io.
wor
k is
thus
for
med
.G
reat
str
engt
h an
d ri
gidi
ty o
f th
e co
mbi
natio
n ar
eby
thes
e m
eans
ens
ured
.Fo
r te
leph
one
circ
uits
itis
impe
rativ
eth
at th
e w
ires
sho
uld
run
in u
nifo
rm s
quar
es, a
nd "
H"
pole
s ar
e be
stsu
ited
for
this
arr
ange
men
t.Sk
etch
es o
f "
A "
and
" H
" p
oles
are
sho
wn
ui F
igs.
109
and
110
res
pect
ivel
y.
184
NO
TE
S O
N T
EL
EG
RA
PHY
.
A s
tay
is m
ade
of th
ree
or m
ore
iron
wir
es tw
iste
d to
geth
er in
long
turn
s.O
ne e
nd o
f th
e st
ay is
pas
sed
twic
e ro
und
the
pole
and
fix
ed w
ithst
aple
s.lh
e ex
act p
ositi
on o
n th
e po
le f
or a
sta
y to
be
secu
red
is k
now
nas
the
" re
sulta
nt p
oint
." I
t is
mid
way
bet
wee
n th
e to
p an
d bo
ttom
wir
eson
the
pole
, and
is w
here
the
effe
ct o
f th
e jo
int f
orce
s is
gre
ates
t. T
he e
ndof
the
stay
is s
plic
ed b
ack
into
the
stay
itse
lf, b
oth
at th
e up
per
and
low
eren
d. T
he s
plic
e is
mad
e by
fir
st s
elec
ting
one
of th
e w
ires
and
turn
ing
it ou
tat
rig
ht a
ngle
s. T
he r
emai
ning
wir
es a
re th
en la
id lo
ngitu
dina
lly a
long
the.
stay
and
the
sele
cted
wir
e w
ound
nea
tly a
roun
d th
em. A
t the
term
inat
ion
ofth
is w
indi
ng o
ne o
f th
e re
mai
ning
wir
es is
sel
ecte
d an
d si
mila
rly
deal
tw
ith, u
ntil
the
trea
tmen
t has
bee
n ex
tend
ed to
the
who
le n
umbe
r of
stra
nds.
At t
he lo
wer
end
of
the
stay
a s
tay
-rod
, fitt
ed w
ith a
scr
ew f
ortig
hten
ing
purp
oses
, is
atta
ched
to a
bau
lk o
f "
pres
erve
d "
timbe
r at
one
end
and
to th
e st
ay a
t the
oth
er.
Bef
ore
splic
ing
the
stay
, whe
re it
conn
ects
with
the
rod,
it is
loop
ed a
roun
d an
iron
thim
ble,
and
the
latte
rpa
sses
thro
ugh
the
eye
of th
e ro
d.T
he h
ole
for
the
pres
erve
d tim
ber
atta
ched
to th
e st
ay is
und
ercu
t in
the
dire
ctio
n of
the
pole
.T
his
unde
r-cu
tting
ens
ures
the
timbe
r be
ing
bank
ed a
gain
st s
olid
ear
th.
A s
trut
is s
ecur
ed a
t its
bas
e by
a p
iece
of
timbe
r, a
nd s
carf
ed a
t its
top
to f
it th
e po
le, w
here
it is
atta
ched
with
a b
olt.
The
join
t is
pain
ted
or ta
rred
to p
reve
nt d
ecay
.A
bout
mid
way
a ti
e ro
d is
use
d to
bin
d th
epc
lo a
nd s
trut
toge
ther
.Po
les
erec
ted
in e
leva
ted
posi
tions
and
on
railw
ayro
utes
, eve
n w
here
a c
urve
is b
ut s
light
, are
dou
ble
-sta
yed.
Stru
ts a
ndst
ays
shou
ld m
ake
as g
reat
an
angl
e as
pos
sibl
e w
ith th
e po
le u
p to
90d
eg.,
for
the
actu
al s
tres
s is
inve
rsel
y pr
opor
tiona
l to
the
dist
ance
bet
wee
n th
elo
wer
end
of
eith
er s
trut
or
stay
and
the
base
of
the
pole
.A
n ex
tra
stro
ng s
tay
is r
equi
red
for
term
inal
pol
es, a
nd it
s st
reng
th s
houl
d be
equ
alto
all t
he b
reak
ing
stre
sses
of
the
wir
es a
dded
toge
ther
.A
for
ked
orV
-sha
ped
stay
is s
omet
imes
nec
essa
ry. I
t is
fork
ed a
t the
sta
y -r
od, a
nd it
stw
o up
per
ends
are
fix
ed to
the
pole
at e
qual
dis
tanc
es f
rom
the
resu
ltant
poin
t, on
e be
ing
abov
e an
d th
e ot
her
belo
w th
at p
oint
.
Ord
inar
y st
ays
are
atta
ched
to th
e po
les
at r
ight
-an
gles
to th
e lin
eof
the
rout
e, b
ut o
ther
s ar
e us
ed in
a li
ne w
ith th
e po
les.
The
se la
tter
are
fixe
d at
a d
ista
nce
of a
bout
a q
uart
er o
f a
mile
apa
rt, a
nd p
reve
ntm
any
span
s of
wir
e be
ing
pulle
d do
wn
by th
e ac
cide
ntal
col
laps
e of
any
one
span
.T
he to
p of
eac
h po
le is
pai
nted
or
tarr
ed, a
nd a
gal
vani
sed
iron
roo
f,ar
rang
ed tr
ansv
erse
ly to
the
line
of th
e w
ires
, ass
ists
in p
rote
ctin
g th
e po
lefr
om d
ecay
.T
o ea
ch p
ole
an "
ear
th w
ire
" is
sec
ured
with
sta
ples
.T
his
wir
e co
n-du
cts
dire
ct to
ear
th a
ny p
ossi
ble
leak
age
of c
urre
nt d
ue to
def
ectiv
ein
sula
tion.
The
ear
th w
ire
is f
ixed
ben
eath
the
was
her,
whi
ch is
inte
r-po
sed
betw
een
the
head
s of
the
arm
-bo
lts a
nd th
e po
le, a
nd th
en c
ontin
ued
NO
TE
S O
N T
EL
EG
RA
PHY
.I
Nti
to th
e to
p of
the
pole
, whe
re it
act
s as
a li
ghtn
ing
cond
ucto
r,T
hn !
ewer
end
is c
oile
d up
and
em
bedd
ed in
the
soil
at th
e fo
ot o
f th
e bo
lo (
inth
e si
de r
emot
e fr
om th
e tr
affi
c. W
ithou
t suc
h a
wir
e an
y le
akag
e of
our
roill
,w
ould
pas
s fr
om o
ne w
ire
into
oth
ers
upon
the
sam
e su
ppor
t, an
d pe
ssi
inte
rfer
e w
ith p
assi
ng s
igna
ls.
Whe
n a
line
wir
e is
run
alo
ng th
e to
ps o
f po
les
" sa
ddle
" b
rack
ets
supp
ort
the
insu
lato
rs,
but w
here
mas
onry
wor
kis
utili
sed
assu
ppor
ts th
e "
brid
ge "
bra
cket
, whi
ch is
an
iron
abu
tmen
t, is
em-
ploy
ed.
" Sh
ackl
es "
are
som
etim
es u
sed
on te
rmin
al p
oles
, but
they
are
elec
tric
ally
uns
ati'
fact
ory,
as
a do
uble
con
nect
ion
with
the
arm
is n
eces
sary
.Sp
ecia
lly s
tron
g in
sula
tors
, how
ever
, are
usu
ally
ado
pted
for
this
pur
pose
.T
he a
rms
to w
hich
the
insu
lato
r sp
indl
es a
re b
olte
d ar
e of
wel
l -se
ason
ed o
ak le
t int
o sl
ight
inci
sion
s up
on th
e "
up "
sid
e of
the
pole
s, a
ndbo
lted
thro
ugh
the
latte
r. T
he a
rms
are
freq
uent
ly o
f un
equa
l len
gths
upo
nth
e sa
me
pole
to e
nsur
e a
brok
en w
ire
falli
ng c
lear
of
othe
rs b
enea
th it
.
Wir
ing.
-The
wir
e is
run
out
fro
m th
e dr
ums
upon
whi
ch it
is c
oile
dan
d th
en li
fted
into
pos
ition
upo
n th
e ar
ms
of th
e po
les.
It is
then
stra
ined
up
to a
llow
of
the
requ
ired
dip
or
sag,
due
reg
ard
bein
g pa
id to
the
time
of y
ear
at w
hich
the
wor
k is
don
e.A
sm
alle
r ac
tual
dip
isgi
ven
in th
e w
inte
r th
an in
the
sum
mer
, to
allo
w f
or a
per
cept
ible
expa
nsio
n w
ith a
n in
crea
se o
f te
mpe
ratu
re.
Thi
s w
ork,
how
ever
, is
gene
rally
don
e in
the
sum
mer
mon
ths.
The
dra
w -
tong
s ar
e us
ed f
orst
rain
ing
up th
e w
ires
, and
a te
nsio
n ra
tche
t and
indi
cato
r en
sure
the
prop
er s
tres
s be
ing
appl
ied.
The
wir
e sh
ould
not
be
so s
lack
at i
tsgr
eate
st d
ip a
s to
pro
duce
con
tact
with
oth
er w
ires
, nor
too
tight
toca
use
its b
reak
age.
The
sta
ndar
d di
p to
sui
t tem
pera
ture
var
iatio
nsis
fou
nd f
rom
the
follo
win
g fo
rmul
a
a =
2w 8s
whe
re1
= th
e le
ngth
of
the
span
in f
eet,
d =
the
dip
in f
eet,
w =
the
wei
ght i
n lb
s. p
er f
oot,
s =
the
stre
ss in
lbs.
It w
ill th
us b
e se
en th
at f
or c
ompa
riso
ns w
hen
othe
r co
nditi
ons
are
equa
l the
dip
is d
irec
tly p
ropo
rtio
nal t
o th
e sq
uare
of
the
span
.A
s th
eac
tual
leng
th (
L)
per
span
of
wir
e is
gre
ater
than
the
dist
ance
fro
m p
ole
to p
ole,
on
acco
unt o
f th
e di
p, a
noth
er f
orm
ula
for
this
is n
eede
d, v
iz. ;
L =
I +
8d,
:31
A s
afet
y fa
ctor
of
four
is a
lway
s al
low
ed in
reg
ard
to th
e di
p, s
o th
at a
186
NO
TE
S O
N T
EL
EG
RA
PHY
.
wir
e is
onl
y st
rain
ed u
p to
a q
uart
er o
f its
brea
king
str
ess.
The
bre
akin
gst
ress
of
a w
ire
is d
irec
tly p
ropo
rtio
nal t
o th
ew
eigh
t per
uni
t len
gth,
or
the
area
of
the
cros
s se
ctio
n.
For
wir
es o
f th
e sa
me
mat
eria
l,ir
resp
ectiv
e of
thei
r w
eigh
ts, t
he s
ame
dip
with
the
sam
e pr
opor
tiona
l str
ain
isre
quir
ed.
Cop
per
has
a hi
gher
co -
effi
cien
t of
expa
nsio
n th
an ir
on, c
onse
quen
tly th
is m
etal
and
iron
shou
ld b
e us
ed to
geth
er o
nly
upon
spa
ns n
ot e
xcee
ding
80
yard
s in
leng
th,
or c
onta
cts
will
pro
babl
y en
sue.
For
line
wir
es th
ew
eigh
t per
mile
rep
rese
nts
the
stan
dard
gaug
e, 2
51bs
. per
sta
tute
mile
bei
ng th
eun
it fi
xed,
and
all
othe
r ca
lcul
atio
nsar
e ba
sed
upon
thes
e fi
gure
s.T
hete
rm "
ohm
-m
ile "
sig
nifi
es th
e w
eigh
t in
lbs.
per
mile
mul
tiplie
d by
the
resi
stan
ce p
er m
ile.
It is
a c
onst
ant,
and
is u
sed
toco
mpa
re th
e co
n-du
ctiv
ity o
f va
riou
s ga
uges
of
wir
e.
Bin
ding
.-T
he w
ire
is b
roug
ht in
to th
egr
oove
of
the
insu
lato
r, a
nd, i
fir
on w
ire
is u
sed
for
the
cond
ucto
r it
is b
ound
on w
ith N
o. 1
6 ga
uge
galv
anis
ed ir
on w
ire,
whi
ch is
rel
ativ
ely
thin
.
In a
ttach
ing
the
cond
ucto
r to
the
insu
lato
rth
e bi
ndin
g w
ire
is w
ound
twic
e ov
er th
e lin
e w
ire
upon
one
sid
e of
the
insu
lato
r, th
e en
d ne
ares
t the
insu
lato
r is
pas
sed
roun
d it
in th
egr
oove
, and
und
er th
e lin
e w
ire
in o
netu
rn u
pon
the
othe
r si
de o
f th
e in
sula
tor.
The
bin
der
is th
en ta
ken
back
roun
d th
e in
sula
tor
and
give
n a
doze
n ne
at tu
rns
alon
g th
e le
ngth
of
the
line
wir
e.T
he o
ther
end
of
the
bind
er is
bro
ught
und
erth
e lin
e w
ire,
rou
ndth
e in
sula
tor
and
over
the
lino
wir
eup
on th
e ot
her
side
, and
giv
en a
doz
enla
ps a
long
the
leng
th o
f th
e lin
e as
des
crib
ed b
efor
e.
In b
indi
ng c
oppe
r w
ire,
how
ever
,a
copp
er ta
po is
wra
pped
rou
nd th
elin
e w
ire
and
exte
nded
to a
sho
rt d
ista
nce
upon
eac
h si
de o
f th
e in
sula
tor.
Abi
ndin
g w
ire
som
ewha
t sim
ilar
to th
e co
nduc
tor
is f
latte
ned
at it
s en
ds a
ndpa
ssed
rou
nd th
e in
sula
tor
groo
ve.
One
end
is th
en b
roug
ht o
ver
and
the
othe
r un
der
the
cond
ucto
r, a
nd e
ach
isca
refu
lly w
ound
alo
ng th
e le
ngth
of th
e co
pper
tape
.
Whe
n on
e co
mpl
ete
leng
th h
as b
een
run
off
the
drum
its
end
isjo
ined
to th
e be
ginn
ing
of a
fre
sh le
ngth
.T
he "
Bri
tann
ia "
join
t is
the
popu
lar
met
hod
of e
ffec
ting
the
nece
ssar
y co
nnec
tion
with
bot
hco
pper
and
iron
aer
ial w
ires
.T
he e
nds
of th
e co
nduc
tor
are
care
fully
cle
aned
and
laid
sid
e by
sid
e fo
r at
leas
t tw
o in
ches
.T
he o
rdin
ary
bind
er, u
sed
at th
ein
sula
tor,
is th
en w
ound
tigh
tly a
roun
d th
e tw
oen
ds, c
omm
enci
ng a
t the
cent
re o
f th
e jo
int,
brin
ging
them
into
clo
seco
ntac
t.T
he b
indi
ng is
cont
inue
d fo
r a
shor
t dis
tanc
eup
on e
ach
side
of
the
join
t.U
pon
this
aco
atin
g of
Bak
er's
flu
id is
sm
eare
d, a
nd th
e w
hole
isfi
nally
sol
dere
d, to
form
a m
ass
of m
etal
and
mai
ntai
n th
e el
ectr
ical
cont
inui
ty o
f th
e lin
e.T
he e
nds
are
then
cut
clo
se to
the
bind
erto
pre
vent
ent
angl
emen
t with
othe
r w
ires
whe
n th
ey a
re s
way
ing.
-
NO
TE
S O
N T
t Lta
ltAtil
V.
187
Tha
line
s ar
esy
stem
atic
ally
num
bere
d in
the
follo
win
g m
anne
r :-
No.
0 is
alw
ays
at th
eto
p of
the
pole
.Fr
om a
pos
ition
on
the
" up
"si
de o
f th
e po
le, w
here
the
arm
s ar
e fi
xed,
No.
1, u
pon
a fo
ur w
ire
arm
ison
the
extr
eme
left
of
the
top
arm
and
No.
2on
the
extr
eme
righ
t, th
ein
ner
left
-han
d w
ire
bein
g N
o. 3
and
the
inne
r ri
ght-
hand
wir
e N
o. 4
, and
so o
n.A
ll od
d nu
mbe
rs a
ro th
usup
on th
e le
ft s
ide
of th
e po
lo a
nd a
llev
ens
upon
the
righ
t sid
e.T
erm
inat
ed w
ires
are
bro
ught
to s
peci
ally
stro
ng in
sula
tors
and
" le
adin
g in
" w
ires
fro
mth
e te
rmin
al p
oles
are
mad
e of
cop
per
cove
red
with
gutta
-per
cha,
and
sur
roun
ded
with
tarr
edhe
mp,
whi
ch la
tter
acts
as
an e
ffic
ient
prot
ectin
g m
ater
ial.
FIG
: Ili
The
wir
es a
re le
d in
to a
woo
den
casi
ng w
hich
ext
ends
alon
g th
e le
ngth
of th
e po
le ;
a le
adin
g -i
n cu
p, th
roug
h w
hich
the
cond
ucto
rco
nnec
ted
toth
e lin
e w
ire
is r
un is
then
fitt
ed to
the
pole
as
show
n in
Fig
. 111
.T
his
cup
prev
ents
moi
stur
e en
teri
ng a
t the
junc
tion
of th
e ou
tsid
e an
din
side
sec
tions
of
the
wir
es.
Whe
n an
iron
wir
e is
bro
ught
toa
copp
erw
ire
both
are
eith
er te
rmin
ated
or
run
into
sep
arat
e gr
oove
sof
a"
Lan
gdon
" in
sula
tor,
the
" ta
ils "
bein
g br
ough
t ove
r th
e in
sula
tor
and
join
ed to
geth
er.
Insi
de th
e of
fice
the
bund
les
of w
ires
are
now
laid
inir
on c
hann
ellin
g,th
e in
divi
dual
wir
es b
eing
insu
late
d w
itha
mix
ture
of
cotto
n an
d m
ilk.
Seve
ral w
ires
are
then
gro
uped
and
a le
adsh
eath
ing
surr
ound
s (a
toll
grou
p.T
hese
pre
caut
ions
are
mad
e to
prev
ent e
xten
sive
&am
igo
from
fire
, whi
ch w
ould
pro
babl
y en
sue
if g
utta
-per
cha
cove
red
wir
esw
uru
used
.
188
NO
TE
S O
N T
EL
EG
RA
PHY
.
Whe
n w
ires
are
sus
pend
ed o
ver
hous
etop
s ir
on p
oles
and
the
best
ma'
e-
rial
s ge
nera
lly a
re e
mpl
oyed
.T
o re
duce
obj
ectio
nabl
e vi
brat
ions
a c
hain
is f
requ
ently
atta
ched
to th
e lin
e w
ire
and
hold
s it
to a
" s
hack
led
" in
su-
lato
r; b
ut a
str
and
of c
oppe
r is
mor
e ef
fect
ive
than
the
chai
n.A
n ir
onba
nd s
houl
d al
way
s en
circ
le a
chi
mne
y st
ack
in p
refe
renc
e to
fix
ing
abr
acke
t to
it, a
nd c
oppe
r w
ire,
on
acco
unt o
f its
dur
abili
ty, i
s al
way
s pr
e-fe
rred
as
the
cond
ucto
r.T
he s
uppo
rts
are
stay
ed in
eve
ry p
ossi
ble
dire
c-tio
n, a
nd th
e w
ires
sho
uld
cros
s bu
sy th
orou
ghfa
res
at r
ight
ang
les.
The
sepr
ecau
tions
aro
impe
rativ
e to
min
imis
e ri
sks
of d
amag
e an
d ac
cide
nts
due
to f
allin
g w
ires
or
supp
orts
.
UN
DE
RG
RO
UN
D C
ON
STR
UC
TIO
N.
In la
rge
tow
ns a
nd c
ities
the
aeri
al o
r op
en s
yste
m o
f co
nstr
uctio
n is
not p
ract
icab
le, s
o it
beco
mes
nec
essa
ry to
ado
pt a
n un
derg
roun
d sy
stem
.T
he in
itial
cos
t of
subt
erra
nean
wor
k is
ver
y gr
eat,
and
the
stri
ctes
tat
tent
ion
is g
iven
to e
very
det
ail o
f th
e w
ork.
The
slig
htes
t def
ect e
xist
-in
g at
the
outs
et is
liabl
e to
cau
se e
ndle
ss tr
oubl
e an
d ex
pens
e, c
onse
-qu
ently
the
best
mat
eria
l and
wor
kman
ship
are
ess
entia
l to
ensu
re a
com
plet
e su
cces
s.W
hen
the
syst
em is
in o
r ad
jace
nt to
a to
wn
a tr
ench
is d
ug, p
refe
rabl
yal
ong
a fo
otpa
th ;
but u
pon
coun
try
road
s w
aste
land
at t
he s
ide
of th
ero
ad is
the
posi
tion
usua
lly s
elec
ted
for
the
oper
atio
n, th
e ob
ject
bei
ng to
avoi
d pr
obab
le d
amag
e to
the
pipe
s, e
tc.,
due
to th
e he
avy
traf
fic
of th
ero
ads
and
stre
ets.
In d
iggi
ng th
e tr
ench
sha
rp c
urve
s an
d th
e cr
ossi
ng o
f th
orou
ghfa
res
are
avoi
ded,
and
whe
re a
dif
fere
nce
of le
vel i
s a
nece
ssity
the
incl
ine
ism
ade
as g
radu
al a
s po
ssib
le.
The
bed
of
the
tren
ch is
als
o m
ade
firm
whe
re lo
ose
eart
h pr
evai
ls, a
nd la
rge
ston
es a
re r
emov
ed w
here
thei
rpr
esen
ce is
like
ly to
cau
se s
ubse
quen
t dam
age
to th
e pi
pes.
The
latte
rar
e us
ually
cas
t fro
m g
ood
qual
ity s
oft p
ig -
iron
, and
thei
rin
tern
aldi
amet
er is
3in
. or
4in.
The
upp
er e
xter
ior
surf
ace
of th
e pi
pes
shou
ldbe
bur
ied
to a
dep
th o
f ab
out 2
ft. b
elow
the
leve
l of
the
foot
way
, and
flus
h bo
xes,
for
dra
win
g -i
n pu
rpos
es, a
re f
itted
at i
nter
vals
of
100y
ds.
Eve
ry f
ourt
h bo
x is
cal
led
a "
join
ting
" bo
x be
caus
e th
e w
ires
, bei
ng m
ade
in le
ngth
s of
400
yds.
, req
uire
to b
e jo
inte
d at
suc
h po
ints
.
The
pip
es a
re c
aref
ully
exa
min
ed f
or f
law
s, s
peci
al a
ttent
ion
bein
g pa
idto
the
inte
rior
of
the
pipe
s w
ith a
vie
w o
f re
mov
ing
excr
esce
nces
, the
pres
ence
of
whi
ch w
ould
des
troy
the
insu
latin
g m
ater
ial o
f th
e w
ires
duri
ng th
e pr
oces
s of
" d
raw
ing
in."
The
pip
e3 a
re h
eate
d an
d di
pped
into
a m
ixtu
re o
f co
al -
tar,
tallo
w, q
uick
lime,
res
in, a
nd n
apht
ha a
t the
requ
ired
tem
pera
ture
, and
a g
laze
is b
y th
is m
eans
impa
rted
to th
em.
The
y ar
e m
ade
in le
ngth
s of
Gft
. or
9ft.,
and
thre
e le
ngth
s ar
e jo
inte
dto
geth
er b
efor
e la
ying
in.
The
join
ts a
re m
ade
air
and
gas
-tig
ht, y
arn,
NO
TE
S O
N T
EL
EG
RA
PHY
.18
9
clay
, and
mol
ten
lead
bei
ng u
sed
for
the
purp
ose.
To
faci
litat
e th
edr
awin
g -i
n pr
oces
s a
wir
e is
thre
aded
thro
ugh
the
pipe
s w
hen
they
are
bein
g la
id.
To
prev
ent d
amag
e to
the
insu
latin
g m
ater
ial m
ats
are
plac
ed in
the
boxe
s, a
nd r
olle
rs a
t the
end
s of
the
pipe
s. T
he s
pigo
t end
of
the
pipe
, and
not
the
sock
et e
nd, i
s al
way
s br
ough
t int
o a
flus
h bo
x.Pi
llar
test
box
es a
re f
ixed
at c
erta
in in
terv
als,
and
bri
ck m
anho
les
built
whe
re s
ever
al c
ondu
its c
once
ntra
te.
The
re a
re tw
o ki
nds
of m
ater
ial i
n ge
nera
l use
for
insu
latin
g un
der-
grou
nd w
ires
, i.e
., gu
tta-p
erch
a or
indi
a-ru
bber
, and
spe
cial
ly p
repa
red
anhy
drou
s pa
per
man
ufac
ture
d in
a p
erfe
ctly
dry
atm
osph
ere.
For
gut
ta-
perc
ha c
able
s a
copp
er c
ondu
ctor
of
abou
t GO
mils
dia
met
er a
nd w
eigh
ing
abou
t 401
bs. p
er m
ile is
use
d, a
nd th
e st
anda
rd d
iam
eter
of
the
core
is 1
74m
ils.
The
cop
per
wir
e, h
avin
g a
cond
uctiv
ity o
f 10
0 pe
r ce
nt.,
has
are
sist
ance
of
abou
t 22
stan
dard
ohm
s pe
r m
ile a
t 75d
eg. F
ah.,
whi
le th
ein
duct
ive
capa
city
mus
t not
exc
eed
.29
mic
ro -
fara
d pe
r m
ile.
As
a pr
o-te
ctio
n to
the
insu
latin
g m
ater
ial a
pre
pare
d ta
pe is
wou
nd a
roun
d ea
chw
ire,
or
arou
nd g
roup
s of
fou
r in
the
case
of
a qu
adru
ple
cabl
e.
For
tele
phon
e w
ork
quad
rupl
ed c
ores
are
used
, and
the
pair
s ar
esy
mm
etri
cally
twis
ted
to p
re%
ent
indu
ctiv
e di
stur
banc
e.T
he w
ires
are
num
bere
d fr
om o
ne u
pwar
ds w
here
the
num
ber
of w
ires
in a
cab
le is
limite
d ;
but w
here
a g
reat
man
y w
ires
rad
iate
suc
h a
syst
em b
ecom
es le
sspr
actic
able
.T
hey
are
then
num
bere
d in
sec
tions
.
Prob
ably
the
mos
t im
port
ant w
ork
of th
e su
bter
rane
an s
yste
m is
the
join
ting
ofth
e va
riou
s le
ngth
s.C
lean
lines
s an
d go
od h
ealth
of
the
wor
kmen
are
abs
olut
ely
esse
ntia
l. T
he w
ires
are
cut
to a
uni
form
leng
th,
and
the
tape
stri
pped
back
for
adi
stan
ceof
abou
t15
in.
and
fast
ened
rou
nd th
e ca
ble.
The
gut
ta-p
erch
a is
then
rem
oved
for
abo
ut
two
inch
es f
rom
the
ends
of
the
two
wir
es to
be
join
ed, g
roat
car
e be
ing
take
n no
t to
" ni
ck "
the
cond
ucto
rs. T
he la
tter
are
then
scr
aped
per
fect
lycl
ean.
Hal
f -a
n -i
nch
from
the
gutta
-per
cha
the
two
wir
es a
re c
ross
ed a
ndth
e en
ds tw
iste
d by
mea
ns o
f pl
iers
.T
he s
uper
fluo
us e
nds
are
rem
oved
and
the
join
t sol
dere
d.R
esin
is u
sed
with
all
sold
erin
g of
this
kin
d.T
he g
utta
-per
cha
is m
ade
war
m f
or a
bout
two
inch
es o
f its
leng
th, a
ndon
esi
deof
itis
draw
nha
lf -
way
ove
rth
etw
iste
dw
ires
.T
heot
her
side
ofth
e gu
tta-p
erch
a is
then
wor
ked
dow
n to
mee
tth
efi
rst
port
ion,
tool
ed w
itha
heat
edir
on a
nd m
ade
toov
erla
pit.
The
who
le o
fth
e gu
tta-p
erch
a co
veri
ngth
e jo
int
is w
arm
ed a
ndw
orke
d w
ith th
e fi
nger
and
thum
b in
to a
hom
ogen
eous
mas
s, a
nd a
llow
edto
set
.C
hatte
rton
's c
ompo
und
is th
en a
pplie
d at
the
cent
reof
the
join
t.A
gut
ta-p
erch
a ta
pe, G
in. l
ong
and
lin. w
ide,
is th
orou
ghly
war
med
thro
ugh,
then
wou
nd a
roun
d th
e jo
int a
nd w
orke
d do
wn
with
the
fing
er a
ndth
umb
until
it s
prea
ds o
ver
abou
t 4iin
. Whe
re th
e en
ds o
f th
is ta
pe m
eet t
heun
dist
urbe
d gu
tta-p
erch
a th
e ta
pe is
tool
ed d
own
; the
join
t is
then
soa
ped
196
tiOht
8 O
N T
EL
Ean
/erI
leY
,
over
, and
the
prep
ared
bin
ding
tape
, as
an o
uter
pro
tect
ion,
is w
rapp
edar
ound
the
gutta
-per
cha.
Dur
ing
thes
e op
erat
ions
exc
essi
ve m
oist
ure,
ove
r-he
atin
g of
the
gutta
-per
cha,
and
dec
entr
alis
atio
n of
the
cond
ucto
rs m
ust
be p
artic
ular
ly a
void
ed,
Dry
Cor
e, o
r Pa
per
Cab
les.
-The
se c
able
s re
sult
in e
cono
my
of s
pace
,re
lativ
ely
smal
lco
st,
very
hig
h in
sula
tion
resi
stan
ce,
and
a qu
arte
rth
eel
ectr
o-st
atic
capa
city
ofei
ther
gutta
-per
cha
orin
dia-
rubb
er-c
over
edca
bles
.T
heel
ectr
o-st
atic
capa
city
per
mile
of
a
pape
r -c
over
ed w
ire
of 2
01bs
. or
401b
s. w
eigh
t per
mile
may
be
as lo
w a
s08
mic
ro -
fara
d, w
hile
that
of
a 10
01bs
. wir
e is
onl
y .1
.T
ao te
sts
for
this
are
mad
e w
ith a
ll th
e ot
her
wir
es in
the
cabl
e an
d th
e sh
eath
ing
toea
rth.
Thi
s lo
w c
apac
ity is
one
of
the
grea
test
adv
anta
ges
in c
onne
ctio
nw
ith te
leph
ony.
As
rega
rds
econ
omy
of s
pace
, abo
ut f
our
times
the
num
-be
r of
wir
es c
an b
o la
id in
a g
iven
spa
ce w
hen
pape
r is
sub
stitu
ted
for
gutta
-per
cha.
The
cos
t for
pip
es is
ther
efor
e co
nsid
erab
ly le
ss.
The
pap
eris
wou
nd o
n sp
iral
ly o
r lo
ngitu
dina
lly, a
nd, i
f ca
refu
lly m
anuf
actu
red
and
appl
ied
as r
egar
ds d
ryne
ss, a
nd a
fter
war
ds k
ept f
ree
from
moi
stur
e, it
is
prac
tical
ly im
peri
shab
le.
The
ele
ctri
fica
tion
of a
pap
er c
able
, too
, is
com
-pa
rativ
ely
slig
ht, a
nd th
ere
is li
ttle
risk
of
the
insu
latio
n br
eaki
ng d
own,
exce
pt th
roug
h de
fect
ive
shea
thin
g or
join
ting,
in w
hich
cas
es a
ll th
ew
ires
in o
ne c
able
are
liab
le to
be
affe
cted
.O
ne w
ire
of a
pai
r is
insu
late
dw
ith w
hite
pap
er, w
hile
the
othe
r is
mad
e di
stin
ctiv
e by
the
use
ofco
lour
ed p
aper
.T
he p
air,
aft
er th
e w
ire
has
been
twis
ted,
isfu
rthe
rin
sula
ted
with
ano
ther
pap
er c
over
ing,
and
the
cabl
e is
then
mad
e up
inla
yers
,ea
ch la
yer
bein
gtw
iste
dop
posi
tely
toth
ead
jace
ntla
yers
toob
viat
e th
eef
fect
sof
indu
ctio
n.A
smal
lai
rsp
ace
isle
ft b
etw
een
the
insu
late
d co
nduc
tors
and
the
lead
she
athi
ng, s
o th
at d
ryai
r m
ay b
e fo
rced
into
the
cabl
e.T
he in
sula
tion
resi
stan
ce p
er m
ile,
with
all
othe
r co
nduc
tors
and
the
shea
thin
g to
ear
th s
houl
d no
t be
less
than
10,
000
meg
ohm
s, a
nd it
som
etim
es r
each
es 2
00,0
00 m
egoh
ms
at50
deg
. Fah
., af
ter
one
min
ute'
s el
ectr
ific
atio
n.A
s lig
htni
ng d
isch
arge
sac
t ser
ious
ly u
pon
pape
r ca
bles
ext
ra p
reca
utio
ns h
ave
to b
e m
ade
to p
reve
ntda
mag
e by
them
.Pr
otec
tors
are
ther
efor
e pl
aced
at t
he s
witc
hboa
rds
and
the
ends
of
the
cabl
es.
Pape
r ca
bles
aro
join
ted
at e
very
75
or 2
20 y
ards
, acc
ordi
ng to
the
wei
ght o
f th
e in
divi
dual
wir
es, a
nd d
urin
g th
e op
erat
ion
of jo
intin
g w
etan
d da
mp
air
shou
ld b
e ca
refu
lly e
xclu
ded
from
them
.T
he tw
o en
ds o
f th
eco
nduc
tors
are
bar
ed a
nd, i
f th
eir
diam
eter
s ar
e re
lativ
ely
smal
l, th
e en
ds a
recr
osse
d an
d th
en n
eatly
twis
ted
toge
ther
.T
he e
nd o
f th
e jo
int i
s so
lder
edan
d th
e tw
iste
d po
rtio
n of
the
wir
es is
turn
ed b
ack
para
llel a
nd c
lose
to th
eco
nduc
tor.
A p
aper
sle
eve,
pre
viou
sly
plac
ed u
pon
one
of th
e w
ires
, is
slip
ped
over
the
join
t and
pro
perl
y se
cure
d, a
nd th
e pr
epar
ed p
aper
isw
ound
spi
rally
ove
r ea
ch p
air.
In jo
intin
g th
e la
rge^
dia
met
er w
ires
the
NO
TE
S O
N T
EL
EG
RA
PHY
. 19
1
two
ends
are
cle
aned
and
tinn
ed.
The
y ar
e dr
awn
clos
eto
geth
er,
and
a co
pper
join
ting
slee
veis
bro
ught
ove
r th
e jo
int a
nd s
olde
red,
resi
n be
ing
alw
ays
used
,an
d a
pape
rsl
eeve
is th
en s
lippe
d ov
erth
e co
nnec
tion.
Aft
eral
lth
ew
ires
ofw
hich
the
cabl
eis
com
-po
sed
have
bee
n si
mila
rly
trea
ted
they
are
ser
ved
en,
bloc
with
afu
rthe
r co
veri
ng o
f sp
iral
ly w
ound
insu
latin
g pa
per.
A le
ad s
leev
e is
then
slip
ped
over
the
who
le a
nd s
ecur
ed b
y m
eans
of
care
fully
mad
e pl
umbe
rs'
wip
ed jo
ints
. The
iron
con
tain
ing
pipe
is th
en jo
inte
d by
mea
ns o
f an
iron
slid
e pi
pe, w
hich
is c
aulk
ed a
nd le
aded
, and
the
oper
atio
n is
com
plet
e.A
s dr
ynes
s is
abs
olut
ely
impe
rativ
e in
the
proc
ess
of jo
intin
g ch
arco
albr
azie
rs m
ust b
e fr
eely
use
d, to
geth
er w
ith a
mir
ror
for
dete
ctin
g th
epr
esen
ce o
f m
oist
ure.
To
test
for
the
insu
latio
n re
sist
ance
of
a dr
y co
re c
able
, a b
atte
ryco
m-
pose
d of
300
dry
cel
ls, h
avin
g an
ele
ctro
-mot
ive
forc
e of
450
vol
ts is
empl
oyed
. The
Whe
atst
one
Bri
dge
and
galv
anom
eter
are
qui
te in
adeq
uate
for
this
test
, and
a s
peci
ally
dev
ised
test
ing
set i
s ut
ilise
d.T
he g
al-
vano
met
er, w
hich
is h
oriz
onta
l and
of
an e
xcee
ding
ly s
ensi
tive
char
acte
r, is
wou
nd to
a r
esis
tanc
e of
25,
000
ohm
s.It
is f
itted
with
a s
hunt
, whi
ch is
norm
ally
in c
ircu
it, h
avin
g a
mul
tiply
ing
pow
er o
f 1,
000.
The
inst
rum
ent
is 3
0 tim
es a
s se
nsiti
ve a
s th
e or
dina
ry T
ange
nt g
alva
nom
eter
, and
has
afi
gure
of
mer
it of
.000
41.
The
bat
tery
mus
t be
wel
l -in
sula
ted,
and
all
mas
ses
of m
agne
tic s
ubst
ance
s w
hich
are
liab
le to
be
mov
ed d
urin
g te
stin
gop
erat
ions
mus
t be
take
n fr
om th
e vi
cini
ty o
f th
e ga
lvan
omet
er.
The
cons
tant
of
the
inst
rum
ent
is ta
ken
thro
ugh
a re
sist
ance
of 1
,100
meg
ohm
s, w
hen
a de
flec
tion
of o
ne d
egre
e m
ay b
e ob
tain
ed.
Com
posi
te D
ry -
Cor
e C
able
s co
mpr
ise
a nu
mbe
r of
pape
r -i
nsul
ated
cond
ucto
rs o
f va
ryin
g si
zes.
The
larg
e -s
ized
cond
ucto
rs a
re a
rran
ged
in th
e ce
ntre
of
the
cabl
e,w
hile
the
smal
ler
ones
are
laid
aro
und
them
. The
for
mer
are
use
d fo
r tr
unk
lines
and
the
latte
r fo
r ju
nctio
n ci
rcui
ts a
nd th
e w
ires
of
priv
ate
rent
ers
and
subs
crib
ers
to e
xcha
nges
.T
he s
tand
ard
size
s ar
e ge
nera
lly a
dopt
ed, a
ndal
l the
spac
ein
ath
ree-
inch
cas
t-ir
onpi
pe is
utili
sed.
With
the
exce
ptio
n of
the
met
hod
of s
tran
ding
thes
e co
nduc
tors
the
gene
ral
cons
truc
tion
of th
e ca
ble
coin
cide
s w
ith th
at o
f th
e m
ultip
le d
ry c
ores
alre
ady
desc
ribe
d,
178
NO
TE
t ON
TE
Lse
diut
s13Y
.
CH
APT
ER
XX
IV.
CO
NST
RU
CT
ION
.
The
re a
re tw
o co
mpa
rativ
ely
larg
e se
ctio
ns o
fth
is v
ery
exte
nsiv
ebr
anch
of
tele
grap
hy, v
iz.,
aeri
al, o
r op
en li
nes,
and
sub
terr
anea
n, o
rco
vere
d lin
es.
Eac
h ha
s its
adv
anta
ges
and
disa
dvan
tage
s, b
ut o
nly
the
chie
f po
ints
of
both
sec
tions
can
be
deal
t with
in th
ese
note
s.O
pen
lines
gene
rally
pre
dom
inat
e, o
n ac
coun
t of
thei
r co
mpa
rativ
ely
low
initi
al c
ost
and
the
grea
ter
faci
litie
s w
hich
exi
st f
or th
eir
subs
eque
nt m
aint
enan
ce.
A m
ain
road
or
railw
ay r
oute
is s
elec
ted
for
open
wor
k, th
e fo
rmer
bei
ngpr
efer
red.
The
chi
ef m
ater
ials
for
the
cons
truc
tion
of a
n ae
rial
line
are
suita
ble
cond
ucto
rs, s
uch
as ir
on o
r co
pper
wir
es, s
elec
ted
wel
l -gr
own
pole
sof
gre
at s
tren
gth
for
thei
r su
spen
sion
, and
insu
lato
rs o
f hi
ghre
sist
ance
to in
sula
te th
e w
ires
fro
m th
e su
ppor
ts.
The
tens
ile s
tren
gth
and
dura
bilit
y of
the
wir
es a
re f
acto
rs o
f gr
eat i
mpo
rtan
ce, w
hile
thei
rco
nduc
tivity
, and
, in
cert
ain
case
s, e
lect
ro-m
agne
tic in
ertia
mus
t be
ampl
yco
nsid
ered
.
Iron
is r
elat
ivel
y ch
eap,
and
aft
er a
n ir
on w
ire
has
been
wel
l gal
vani
sed
it is
dur
able
, and
act
s as
an
effi
cien
t con
duct
or f
or g
ener
al p
urpo
ses.
As
iron
is a
mag
netic
sub
stan
ce, h
owev
er, i
t bec
omes
mag
netis
ed w
hile
car
ry-
ing
a cu
rren
t of
elec
tric
ity, a
nd u
nder
thos
e co
nditi
ons
an ir
on w
ire
has
been
like
ned
to a
line
al m
agne
t.T
he a
ct o
f m
agne
tisin
g an
d de
mag
-ne
tisin
g it
prod
uces
del
eter
ious
eff
ects
in te
leph
ony,
and
whe
n fa
st s
peed
wor
king
is r
esor
ted
to.
Con
sequ
ently
, iro
n, o
n ac
coun
t of
its e
lect
ro-
mag
netic
iner
tia, i
s be
ing
rapi
dly
subs
titut
ed b
y co
pper
, the
mar
ket
valu
e of
whi
ch h
as b
een
cons
ider
ably
red
uced
dur
ing
rece
nt y
ears
.
In la
rge
tow
ns, o
r w
hen
in c
lose
pro
xim
ity to
che
mic
al w
orks
, iro
nra
pidl
y de
teri
orat
es th
roug
h th
e ef
fect
s of
atm
osph
eric
che
mis
try
upon
it,w
hile
cop
per
is u
naff
ecte
d, a
nd h
as th
e gr
eat a
dvan
tage
of
bein
g a
bette
r co
nduc
tor.
The
re is
a S
wed
ish
met
hod
ofsm
eltin
g ir
on w
ith c
harc
oal,
and
" ch
arco
al "
iron
pos
sess
es a
hig
her
cond
uctiv
ity th
an th
e or
dina
ry m
etal
.T
he f
orei
gn m
ater
ial h
as b
een
very
fre
ely
used
inco
nseq
uenc
e ;
but
Eng
lish
iron
is n
ow b
eing
util
ised
to a
larg
e ex
tent
.
The
pig
-ir
onis
fir
st p
uddl
ed, a
nd th
en b
eate
n ou
t and
rol
led
into
suita
ble
bars
and
pas
sed
thro
ugh
the
rolli
ng m
ill.
The
latte
r co
nsis
ts o
f a
seri
es o
f ro
llers
gro
uped
in p
airs
whi
ch a
re p
lace
d al
tern
atel
y ho
rizo
ntal
ly a
ndve
rtic
ally
.E
ach
rolle
r is
gro
oved
, and
the
size
of
each
suc
ceed
ing
pair
isre
duce
d an
d th
e sp
eed
of r
otat
ion
incr
ease
d.W
ires
of
a sm
alle
r si
ze th
anth
at o
f th
e sm
alle
st g
roov
e ar
e ob
tain
ed b
y dr
awin
g th
em, w
hen
cold
,
NO
TE
S O
N T
EL
EG
RA
PHY
.17
9
thro
ugh
prop
er d
ies
;bu
t as
this
tend
s to
har
den
the
met
al a
ndin
crea
seits
res
ista
nce,
it is
sub
sequ
ently
ann
eale
d.
To
prev
ent r
ust a
nd c
onse
quen
t mec
hani
cal
dete
rior
atio
n th
e w
ire
isga
lvan
ised
.It
is th
en w
ound
upo
n su
itabl
e dr
ums
topr
even
t " k
inks
."E
ach
leng
th s
houl
d be
fre
e fr
om w
elds
,ci
nder
s, a
nd o
ther
impu
ritie
s, a
llof
whi
ch te
nd to
wea
ken
the
wir
e.A
uni
form
bre
akin
g st
rain
ises
sent
ial,
and
to im
prov
e ea
ch le
ngth
in th
isre
spec
t, th
e w
ire
is n
ot m
ade
from
one
solid
mas
s, -
but f
rom
sev
eral
laye
rs, w
hich
, aft
erm
anuf
actu
re, p
osse
ssth
e ho
mog
enei
ty o
f a
mas
s w
ithan
incr
ease
ddu
ctili
ty.
The
re a
rese
vera
l tes
ts f
or th
e m
echa
nica
l str
engt
h of
a w
ire.
The
latte
r is
pas
sed
alte
rnat
ely
over
and
und
er a
ser
ies
of p
ulle
ys;
it sh
ould
be
bent
bac
k-w
ards
and
for
war
ds a
giv
en n
umbe
r of
times
at r
ight
ang
les
with
out
brea
king
, and
wou
nd u
pon
itsel
f an
d al
so tw
iste
d w
ithou
tsp
littin
g.It
shou
ld c
arry
a c
erta
in w
eigh
t and
res
ist
a sp
ecif
ied
stre
ss w
ithou
t bre
akin
g.
INSU
LA
TO
RS.
The
insu
lato
rs f
itted
to th
e ar
ms
of th
e po
les
are
usua
lly m
ade
ofpo
rcel
ain,
wel
l vitr
ifie
d.G
laze
d ea
rthe
nwar
e is
a c
heap
mat
eria
l, bu
t the
use
of a
n ex
teri
or g
laze
onl
y, w
hich
fre
quen
tly c
rack
s an
d af
ford
sa
chan
nel f
or th
e ac
cum
ulat
ion
of m
oist
ure,
isa
prec
ario
us m
etho
d of
mai
ntai
ning
goo
d in
sula
tion.
Gla
ss h
as b
een
trie
d, b
ut th
at s
ubst
ance
bein
g hy
gros
copi
c an
d br
ittle
has
bee
n ab
ando
ned.
Ebo
nite
has
bee
nex
peri
men
ted
with
, but
its
surf
ace
beco
mes
spo
ngy
and
inde
nted
aft
era
time,
and
the
insu
latio
n co
nseq
uent
ly s
uffe
rs.
The
re a
re s
ever
al f
orm
s of
insu
lato
rs, t
he d
oubl
e -s
hed
or d
oubl
e -c
up p
atte
rn(F
ig. 1
08)
bein
g pr
e-em
inen
tly s
uper
ior
to o
ther
type
s fo
r ge
nera
lpu
rpos
es.
Thi
s pa
ttern
inte
rpos
es a
gre
at a
mou
nt o
f in
sula
ting
surf
ace
betw
een
the
wir
e at
tach
ed to
the
oute
r se
ctio
n an
d th
e m
etal
bol
tsc
rew
ed in
to th
ein
ner
sect
ion,
and
has
a m
inim
um b
ulk.
The
exp
osed
sur
face
of
the
oute
r sh
ed is
kep
t cle
anby
fre
quen
t rai
nst
orm
s, w
hils
t the
inne
r cu
p re
mai
ns d
ry, b
eing
pro
tect
edby
the
oute
ron
e.T
he n
ewes
t kin
d of
dou
ble
-she
d in
sula
tor-
the
" C
orde
aux
"-is
mou
lded
in o
ne p
iece
, and
scr
ews
on to
the
iron
spin
dle
or b
olt.
(Fig
.30
8.)
An
elas
tic r
ing
is c
lam
ped
betw
een
the
insu
lato
r an
d th
esh
ould
erof
the
spin
dle
;it
prev
ents
fra
ctur
e of
the
insu
lato
r du
e to
the
uneq
ual
expa
nsio
n of
the
porc
elai
n an
d sp
indl
e w
hen
the
tem
pera
ture
var
ies.
The
Cor
deau
x in
sula
tor
is a
n im
prov
emen
t upo
n th
e ol
der
type
, in
whi
chce
men
t was
use
d be
twee
n th
e se
ctio
ns o
f th
e in
sula
tor
and
to f
ixth
esp
indl
e to
the
inne
r cu
p.T
o re
mov
e an
old
type
insu
lato
r th
esp
indl
eits
elf
had
to b
e re
mov
ed, a
nd th
is w
as a
ser
ious
dra
wba
ck.
A r
ecen
tly in
trod
uced
insu
lato
r ca
rrie
s a
fuse
and
is te
rmed
the
"fu
se "
insu
lato
r.It
is in
two
sect
ions
, a c
over
bei
ng m
ade
tosc
rew
dow
n ov
er a
Oha
mbe
r at
the
top.
The
line
s ar
e te
rmin
ated
at t
he in
sula
tor,
and
the
194
NO
TE
S O
N T
EL
EG
RA
PHY
.
All
test
ing
offi
ces
are
prov
ided
with
a v
ertic
al "
gal
vano
met
er "
and
test
ing
switc
h, b
y m
eans
of
whi
ch th
epo
sitio
ns o
f fa
ults
may
be
read
ilylo
cate
d be
twee
n tw
ote
stin
g po
ints
.T
he "
gal
vano
met
er"
is p
lace
d in
apr
omin
ent p
ositi
on a
t the
test
-bo
x.T
he s
witc
h is
com
pose
d, o
f fo
ur b
rass
quad
rant
s, s
urro
unde
d by
an
eart
h-c
onne
cted
bra
ss r
ing.
Tw
o of
the
quad
rant
s ar
e co
nnec
ted
to th
epo
les
of a
test
ing
batte
ry, a
thir
d m
arke
dG
to o
ne te
rmin
al o
f th
e"g
alva
nom
eter
," a
nd th
e fo
urth
mar
ked
X to
an
adja
cent
term
inal
at th
e te
st -
box.
The
sec
ond
galv
anom
eter
Fib_
113
,te
rmin
alis
also
conn
ecte
dto
ate
st -
box
term
inal
.T
he a
rran
ge-
men
tis
show
ndi
agra
mat
ical
lyin
Fig.
113.
The
loca
lity
ofdi
scon
nect
ion,
ear
th, a
nd c
onta
ct f
aults
may
be
roug
hly
dete
rmin
edby
the
use
of th
o te
st -
box
" ga
lvan
omet
er "
and
switc
h.In
the
case
of
dis-
conn
ectio
ns th
e te
stin
g po
ints
en
rout
ear
e in
turn
req
uest
ed to
"ea
rth"
the
wir
e.Su
ppos
e th
at a
test
ing
offi
ce m
idw
ay b
etw
een
the
term
inal
offi
ces
has
been
req
uest
ed to
mak
ean
" e
arth
" c
onne
ctio
n.T
he o
ffic
e at
whi
ch th
e te
st is
bei
ng c
ondu
cted
join
s th
e ne
gativ
e po
le o
f th
e ea
rthe
dte
stin
g ba
ttery
to th
e lin
e th
roug
h th
ega
lvan
omet
er, b
y m
eans
of
the
switc
h.If
no
defl
ectio
n is
obs
erve
d th
e lin
eha
s be
en e
arth
ed b
eyon
dth
e fa
ult.
The
oth
er te
stin
g po
ints
on
the
faul
tsi
de a
re th
en s
imila
rly
NO
TE
S O
N T
EL
EG
RA
PHY
.19
5
deal
t with
in tu
rn u
ntil
a de
flec
tion
is o
btai
ned,
and
it is
then
kno
wn
that
the
faul
t exi
sts
betw
een
the
offi
ce a
t whi
ch th
e la
st e
arth
ing
oper
atio
n w
asef
fect
ed a
nd th
e of
fice
whe
re th
e ea
rth
conn
ectio
n es
tabl
ishe
d th
e co
ntin
uity
of th
e ci
rcui
t.
Whe
n an
ear
th f
ault
exis
ts a
som
ewha
t sim
ilar
proc
edur
e is
ado
pted
.In
this
cas
e th
e te
stin
g po
ints
in tu
rn d
isco
nnec
t the
line
, and
at t
he o
ffic
ew
here
the
test
is b
eing
mad
e th
e sa
me
arra
ngem
ents
as
befo
re a
re n
eces
sary
.N
ow, h
owev
er, t
he c
ondi
tions
are
rev
erse
d.A
s lo
ng a
s th
e lin
e is
dis
-co
nnec
ted
beyo
nd th
e fa
ult a
def
lect
ion
is o
bser
ved,
the
curr
ent p
assi
ngto
ear
th a
t the
fau
lt; b
ut a
s so
on a
s th
e di
scon
nect
ion
is m
ade
betw
een
the
test
ing
offi
ce a
nd th
e po
int o
fin
terr
uptio
n, a
def
lect
ion
is n
otob
serv
ed, a
s th
e co
ntin
uity
of
the
circ
uit h
as b
een
brok
en.
The
loca
lity
of th
e ea
rth
faul
t is
thus
det
erm
ined
.
In th
e ca
se o
f a
cont
act b
etw
een
two
lines
the
test
ing
offi
ce jo
ins
one
pole
of
the
eart
h -c
onne
cted
test
ing
batte
ry to
one
of
the
lines
, and
the
othe
r lin
e is
" e
arth
ed "
thro
ugh
the
galv
anom
eter
.A
cur
rent
then
pass
es f
rom
the
firs
t wir
e th
roug
h th
e po
int o
f co
ntac
t to
the
seco
nd w
ire,
and
then
ce to
ear
th th
roug
h th
e te
stin
g ga
lvan
omet
er.
At t
he te
stin
gof
fice
s on
the
line
disc
onne
ctio
ns o
f bo
th w
ires
are
eff
ecte
d, a
nd it
isap
pare
nt th
at w
hen
the
disc
onne
ctio
ns a
re m
ade
betw
een
the
offi
ce c
on-
duct
ing
the
test
and
the
faul
t the
gal
vano
met
er n
eedl
e ce
ases
to b
e de
flec
ted,
but w
hen
the
disc
onne
ctio
ns a
re m
ade
beyo
nd th
e fa
ult t
hey
do n
ot a
ffec
tth
e cu
rren
t pas
sing
fro
m o
ne li
ne to
the
othe
r th
roug
h th
e co
ntac
t, an
dth
e de
flec
tion
is u
ndis
turb
ed.
Inte
rmitt
ent f
aults
are
loca
lised
by
succ
essi
vely
cro
ssin
g se
ctio
ns o
f th
efa
ulty
wir
e w
ith th
ose
of a
wir
e w
hich
is k
now
n to
be
in g
ood
wor
king
orde
r.W
hen
the
faul
t has
bee
n tr
ansf
erre
d fr
om o
ne c
ircu
it to
the
othe
rit
is o
bvio
us th
at th
e in
terr
uptio
n ex
ists
bet
wee
n th
e po
ints
whe
re th
e"
cros
ses
" w
ere
last
eff
ecte
d,
Mea
sure
men
tof
Res
ista
nce.
-The
sim
ples
t met
hod
of m
easu
ring
resi
stan
ce is
to jo
in u
p th
e co
nduc
tor
to b
e te
sted
in c
ircu
it w
ith a
bat
tery
and
galv
anom
eter
.T
he d
efle
ctio
n pr
oduc
ed o
n th
e ga
lvan
omet
er s
houl
dbe
not
ed a
nd th
en a
sui
tabl
e se
t of
resi
stan
ce c
oils
sub
stitu
ted
for
the
con-
duct
or.
The
coi
ls s
houl
d be
man
ipul
ated
unt
il th
e sa
me
defl
ectio
nis
obta
ined
as
whe
n th
e co
nduc
tor
form
ed p
art o
f th
e ci
rcui
t.T
he r
esis
tano
oof
the
coils
will
then
be
the
sam
e as
that
of
the
cond
ucto
r un
der
test
, as
will
be
read
ily u
nder
stoo
d by
an
appl
icat
ion
of O
hm's
law
.A
noth
er m
etho
d of
mea
suri
ng r
esis
tanc
e is
by
the
use
of a
dif
fere
ntia
lga
lvan
omet
er.
The
obj
ect u
nder
test
is jo
ined
to o
ne o
f its
coi
ls a
nd to
the
othe
r co
il is
join
ed a
set
of
adju
stab
le r
esis
tanc
es.
The
gal
vano
met
eris
join
ed in
"se
ries
," a
nd a
t the
junc
tion
of it
s co
ils a
bat
tery
is c
onne
cted
.T
he a
rran
gem
ent i
s sh
own
in F
ig. 1
14, b
ut it
sho
uld
be u
nder
stoo
d th
a t
if a
n ea
rthe
d lin
e is
und
er te
st it
will
be
nece
ssar
y to
ear
th th
e ba
ttery
and
the
resi
stan
ce c
oils
.T
he la
tter
shou
ld b
e m
anip
ulat
ed u
ntil
no d
efle
ctio
nti
2
196
NO
TE
S O
N T
EL
EG
RA
PHY
.
of th
e ga
lvan
omet
er n
eedl
e is
obs
erve
d.T
he c
urre
nt f
rom
the
batte
rysp
lits
thro
ugh
the
two
galv
anom
eter
coi
ls, a
nd, i
f th
e re
sist
ance
s of
the
two
path
s ar
e eq
ual,
the
curr
ent w
ill d
ivid
e in
to tw
o eq
ual p
ortio
ns, w
hich
will
trav
erse
the
coils
of
the
galv
anom
eter
in o
ppos
ite d
irec
tions
.T
heef
fect
of o
ne w
ill c
onse
quen
tly n
eutr
alis
e th
at o
fth
eot
her,
and
the
galv
anom
eter
nee
dle
will
be
unaf
fect
ed.
Thi
s co
nditi
on is
bro
ught
abo
utby
the
adju
stm
ent o
f th
e re
sist
ance
coi
ls.
The
res
ista
nce
requ
ired
in th
ela
tter
to e
ffec
t a b
alan
ce is
the
resi
stan
ce o
f th
e ob
ject
und
er te
st.
Bat
tery
Res
ista
nce.
-The
res
ista
nce
of a
bat
tery
, r, m
ay b
e as
cert
aine
dby
wha
t is
know
n as
the
half
-de
flec
tion
met
hod.
The
bat
tery
is f
irst
join
edup
in c
ircu
it w
ith a
gal
vano
met
er, G
, and
set
of
resi
stan
ce c
oils
, and
the
latte
r is
adj
uste
d un
til a
sui
tabl
e de
flec
tion,
say
, 60
tang
ent d
ivis
ions
, is
obta
ined
.C
all t
he r
esis
tanc
e R
. The
def
lect
ion
is th
en h
alve
d by
an
addi
tion
to th
e re
sist
ance
of
the
coils
, and
, of
cour
se, t
he c
urre
nt in
the
FIG
fl'
circ
uit i
s on
ly h
alf
of it
s fo
rmer
val
ue.
Let
the
requ
ired
res
ista
nce
in th
isin
stan
ce b
e de
note
d by
R2.
But
as
the
curr
ent h
as b
een
halv
ed it
fol
low
sth
at th
e to
tal r
esis
tanc
e is
twic
e w
hat i
t was
in th
e fi
rst c
ase.
Au
equa
tion
may
now
be
stat
ed th
us :-
2 (r
+ G
+ R
1) =
r +
G +
R2
r=
R2
- (2
Ri +
G)
Exa
mpl
e 47
.-W
ith a
gal
vano
met
er h
avin
g a
resi
stan
ce o
f 32
0 oh
ms
(G)
and
a ba
ttery
, the
res
ista
nce
(r)
of w
hich
was
to b
e as
cert
aine
d, a
def
lec-
tion
of 6
0 ta
ngen
t div
isio
ns w
as o
btai
ned
whe
n a
resi
stan
ce o
f 44
0 oh
ms
(1%
) w
as in
sert
ed in
the
resi
stan
ce c
oils
.O
n in
crea
sing
the
resi
stan
ce o
fth
e la
tter
to 1
,240
(R
5) th
e de
flec
tion
was
onl
y 30
tan.
div
isio
ns.
Wha
tw
as th
e re
sist
ance
of
the
batte
ry ?
Ans
wer
.-2
(r +
G +
R1)
= r
+ G
+ R
22
(r +
320
+44
0) =
r +
320
+ 1
,240
2 r
+ 6
40 +
880
= r
320
+ 1
,210
2 r
-f-
1,52
0 =
r +
1,5
60. .
r =
1,5
60 -
1,52
0=
40
Ans
wer
:40
ohm
s.
NO
TE
S O
N T
EL
EG
RA
PHY
.10
7
The
bat
tery
res
ista
nce
may
be
read
ily a
scer
tain
ed b
y ad
ding
twic
e th
esm
alle
r re
sist
ance
to th
at o
f th
e ga
lvan
omet
er a
nd s
ubtr
actin
g th
e re
sult
from
the
larg
er r
esis
tanc
e.
Dim
inis
hed
Def
lect
ion
Met
hod.
-In
the
prec
edin
g te
st th
e or
igin
al d
efle
c-tio
n w
as h
alve
d in
the
seco
nd c
ase
by th
e ad
ditio
n of
res
ista
nce.
It is
not
impe
rativ
e, h
owev
er, t
hat t
his
shou
ld b
e so
,fo
r in
the
" di
min
ishe
dde
flec
tion
" m
etho
d it
is n
ot n
eces
sary
that
the
two
defl
ectio
ns s
houl
d be
in tb
e pr
opor
tion
of tw
o to
one
.
Exa
mpl
e 48
.-It
is d
esir
ed to
det
erm
ine
the
resi
stan
ce o
f a
batte
ry b
ym
eans
of
a ta
ngen
t gal
vano
met
er h
avin
g a
resi
stan
ce o
f 20
ohm
s.B
yjo
inin
g up
the
batte
ry to
the
galv
anom
eter
, tog
ethe
r w
ith a
res
ista
nce
of45
ohm
s, a
def
lect
ion
of 4
0 di
visi
ons
is o
btai
ned,
but
by
incr
easi
ng th
ere
sist
ance
of
the
coils
to 1
20 o
hms
a de
flec
tion
of 2
5 di
visi
ons.
onl
y is
regi
ster
ed.
Wha
t is
the
batte
ry r
esis
tanc
e?
As
the
elec
tro-
mot
ive
forc
e is
the
sam
e in
eac
h ca
se, t
he c
urre
nts,
and
,co
nseq
uent
ly, t
he d
efle
ctio
ns, a
re in
vers
ely
prop
ortio
nal t
o th
eto
tal
resi
stan
ces.
Let
r =
the
batte
ry r
esis
tanc
e,G
= th
e ga
lvan
omet
er r
esis
tanc
e,R
1= th
e fi
rst r
esis
tanc
e in
the
coils
,R
2 =
the
incr
ease
d re
sist
ance
in th
e co
ils,
di =
the
firs
t def
lect
ion,
d2 =
the
dim
inis
hed
defl
ectio
n.
The
n di
:d2
::
r +
G +
R2
r +
G +
Ri
40:
25:
+ 2
0 +
120
: r +
20
+ 4
540
(r
+ 6
5) =
25
(r +
140
)40
r +
260
0 =
25
r +
350
040
r -
25
r =
350
0 -
2600
15 r
= 9
00r
= 6
0A
nsw
er :
60 o
hms.
The
ele
ctro
-mot
ive
forc
e of
a b
atte
ry m
ay b
e de
term
ined
by
the
equa
l?e
flec
tion
met
hod,
in w
hich
the
batte
ry is
join
ed to
a g
alva
nom
eter
and
set o
f re
sist
ance
coi
ls.
The
latte
r is
adj
uste
d un
til a
sui
tabl
e de
flec
tion
is o
btai
ned,
and
the
tota
l res
ista
nce
of th
e ci
rcui
t is
then
not
ed.
In th
ene
xt o
pera
tion
the
batte
ry is
rem
oved
, and
in it
s pl
ace
a. s
tand
ard
cell,
the
elec
tro-
mot
ive
forc
e of
whi
ch is
kno
wn,
is in
sert
ed in
the
circ
uit.
The
resi
stan
ce c
oils
are
aga
in a
djus
ted
until
the
sam
e de
flec
tion
as in
the
firs
tin
stan
ce is
rec
orde
d.A
s th
e cu
rren
ts a
re e
qual
in s
tren
gth
in th
e tw
oca
ses,
it f
ollo
ws
that
the
elec
tro-
mot
ive
forc
es r
equi
red
to p
rodu
ce th
emar
e in
the
sam
e pr
opor
tion
as th
e re
sist
ance
s w
hich
are
ess
entia
l to
198
NO
TE
S O
N T
EL
EG
RA
PHY
.
the
prod
uctio
n of
the
equa
l cur
rent
s.If
E1
and
E2
and
R, a
nd R
2re
pres
ent t
he e
lect
ro-m
otiv
e fo
rces
and
res
ista
nces
res
pect
ivel
y in
the
two
case
s-C
=1
and
C =
but a
s th
e va
lue
of C
is th
e sa
me
in e
ach
case
E1.
E,
: R,
: R2
Exa
mpl
e 49
.-W
ith a
bat
tery
of
50 o
hms
resi
stan
ce jo
ined
to a
gal
vano
-m
eter
of
100
ohm
s re
sist
ance
, and
a s
et o
f re
sist
ance
coi
ls, i
n w
hich
are
sist
ance
of
3,45
0 oh
ms
is in
sert
ed, a
cer
tain
def
lect
ion
is o
btai
ned.
By
the
subs
titut
ion
for
the
batte
ry o
f a
stan
dard
cel
lha
ving
an
elec
tro-
mot
ive
forc
e of
1i v
olt a
nd a
res
ista
nce
of 5
ohm
s it
isne
cess
ary
to u
nplu
g on
ly75
ohm
s to
pro
duce
a s
imila
r de
flec
tion.
Wha
t is
the
elec
tro-
mot
ive
forc
eof
the
batte
ry
Ans
wer
: T
he to
tal r
esis
tanc
e w
hen
the
batte
ry is
in c
ircu
it is
3,6
00 o
hms
(50
100
+ 3
,450
).W
hen
the
stan
dard
cel
l has
bee
n su
bstit
uted
the
resi
stan
ce o
f th
e ci
rcui
t has
bee
n re
duce
d to
180
ohm
s(5
+ 1
00 +
75)
.T
he e
lect
ro-m
otiv
e fo
rce
of th
e ba
ttery
is in
the
sam
e pr
opor
tion
to th
at o
fth
e ce
ll, a
s th
e re
sist
ance
in th
e fi
rst c
ase
is to
that
in th
e se
cond
.E
, ::: R
,: R
2E
, :1.
5:
:3,
600
: 180
180
E, =
3,6
00 x
1.5
=30
Ans
wer
: 30
vol
ts.
The
ans
wer
may
be
veri
fied
by
appl
ying
Ohm
's la
w to
sho
w th
at s
imila
rcu
rren
ts a
re o
btai
ned.
1In
the
firs
t cas
e=
= 8
,603
00 =
120
ampe
re,
2an
d in
the
seco
nd c
ase
C =
=18
0=
120
ampe
re.
TH
E W
HE
AT
STO
NE
BR
IDG
E.
The
Whe
atst
one
Bri
dge
is a
n in
stru
men
t em
ploy
ed f
or m
easu
ring
resi
stan
ces.
It is
usu
ally
dep
icte
d di
agra
mat
ical
ly a
s a
para
llelo
gram
of
resi
stan
ces,
thre
e of
whi
ch r
eally
com
pris
e th
e ac
tual
inst
rum
ent,
the
four
th b
eing
the
unkn
own
resi
stan
ce.
Fig.
115
sho
ws
the
theo
retic
alar
rang
emen
t.T
he o
ppos
ite a
ngle
s of
the
para
llelo
gram
are
" b
ridg
ed,"
in th
e on
e ca
se b
y a
very
sen
sitiv
e ho
rizo
ntal
gal
vano
met
er, a
nd in
the
othe
r by
a b
atte
ry.
Tw
o of
the
resi
stan
ces,
eac
h of
whi
ch is
usua
lly m
ade
up o
f th
ree
coils
of
10, 1
00, a
nd 1
,000
ohm
s re
sist
ance
,ar
ete
rmed
the
ratio
s, a
nd a
re s
how
n in
the
diag
ram
as
a an
d b.
The
thir
dre
sist
ance
of th
ebr
idge
, cal
led
the
rheo
stat
, is
mar
ked
d,an
dis
NO
TE
S O
N T
EL
EG
RA
PHY
.19
9
gene
rally
mad
e up
of
resi
stan
ce c
oils
of
1, 2
, 3, 4
, 10,
20,
30,
40,
100
, 200
,30
0, 4
00, 1
,000
, 2,0
00, 2
,000
, and
4,0
00 o
hms
resi
stan
ce r
espe
ctiv
ely.
Whe
n a
bala
nce
has
been
eff
ecte
d by
the
adju
stm
ent o
f th
e rh
eost
at,
that
is to
say
, whe
n th
e po
ints
A a
nd 0
are
at e
qual
pot
entia
ls a
nd th
ega
lvan
omet
er n
eedl
e is
und
efle
cted
, the
res
ista
nces
of
the
arm
s of
the
brid
ge b
ear
a fi
xed
ratio
to e
ach
othe
r :-
a :b
::d:x
If a
and
b a
re e
qual
in v
alue
, the
n d =
xT
hey
may
be
mad
e un
equa
l, ho
wev
er, b
ut th
e pr
opor
tion
stat
ed a
bove
hold
s go
od.
It is
ess
entia
l tha
t the
rat
ios
a an
d b
shou
ld h
ave
som
e
6.00
0000
/000
/0,0
0.'1
0010 /o
/00
4.k%
,%. /
000
/0
y se
)0
,,000
1600
000
00,4
000
ir:o
0,20
/09
.001
4430
ooer
so.1
'4'2
°oF A
FIG
11S
.
resi
stan
ce, o
r th
e ga
lvan
omet
er w
ould
be
shor
t-ci
rcui
ted
thro
ugh
them
.B
y m
akin
g th
e re
sist
ance
in b
10
or 1
00 ti
mes
as
grea
t as
that
in a
are
sist
ance
equ
al to
10
or 1
00 ti
mes
that
of
the
rheo
stat
(11
,110
ohm
s) m
aybe
mea
sure
d.T
he a
rran
gem
ent o
f th
e co
ils in
the
prac
tical
for
m o
f W
heat
ston
eB
ridg
e is
sho
wn
in F
ig. 1
16.
Tw
o si
mpl
e ke
ys a
re e
mpl
oyed
for
join
ing
up th
e ga
lvan
omet
er a
nd b
atte
ry.
Whe
n th
e re
sist
ance
s of
the
ratio
sha
ve b
een
dete
rmin
ed a
nd b
roug
ht in
to c
ircu
it an
app
roxi
mat
e re
sist
ance
shou
ld b
e un
plug
ged
in th
e rh
eost
at.
The
bat
tery
key
sho
uld
then
be
depr
esse
d an
d th
e ga
lvan
omet
er k
ey ta
pped
mom
enta
rily
so
that
the
200
NO
TE
S O
N T
EL
EG
RA
PHY
.
dire
ctio
n of
the
defl
ectio
nm
ay b
e ob
serv
ed.
The
latte
r ke
y sh
ould
not
be
held
dow
n fi
rmly
at f
irst
, for
, if
a ba
lanc
e ha
s no
t bee
n ef
fect
ed, t
hepa
ssag
e of
a s
tron
g cu
rren
t thr
ough
the
galv
anom
eter
coi
l will
res
ult i
na
viol
ent s
win
ging
of
the
need
le, a
nd m
uch
valu
able
tim
e w
ill o
ften
be
lost
.T
he k
ey m
ay b
e ho
ld d
own
subs
eque
ntly
, how
ever
, whe
n re
-ad
just
men
ts
FIG
, 116
of th
e rh
eost
at h
ave
mod
ifie
d th
e st
reng
th o
f th
ecu
rren
t pas
sing
thro
ugh
the
galv
anom
eter
.T
wo
of th
e pl
ugs
are
mar
ked
INF.
(Inf
inity
), b
y th
ere
mov
al o
f w
hich
the
rheo
stat
may
be
disc
onne
cted
.G
reat
car
e sh
ould
be ta
ken
to k
eep
all t
he p
lugs
cle
an, f
or if
good
con
tact
is n
ot m
ade
C
FIG
117
inco
rrec
t res
ults
will
be
obta
ined
.A
" q
uadr
ant "
sw
itch
for
reve
rsin
gth
e di
rect
ion
of th
e ba
ttery
cur
rent
is a
lso
empl
oyed
.T
he b
atte
ry u
sed
for
test
ing
with
the
Whe
atst
one
Bri
dge
is c
ompo
sed
of D
anie
ll ce
lls, t
he n
umbe
r of
whi
ch v
arie
s fr
om 1
0 to
40, a
ccor
ding
toth
e na
ture
of
the
test
.T
wen
ty D
anie
ll ce
lls m
ay b
l tak
en a
s su
ffic
ient
to p
rovi
de th
e av
erag
e el
ectr
o-m
otiv
e fo
rce.
NO
TE
S O
N T
EL
EG
RA
PHY
.
Res
ista
nce
of a
Loo
p.-I
n th
ere
sist
ance
, tw
o w
ires
are
gen
eral
lyre
sist
ance
, x, a
nd th
e tw
o w
ires
Fig.
117
.
Exa
mpl
e 50
.-If
b dth
en a
:b
ax
and
subs
titut
ing,
201
cond
uctiv
ity te
st, o
r m
easu
rem
ent o
flo
oped
.T
he lo
op is
then
the
unkn
own
are
join
ed a
s sh
own
theo
retic
ally
in
a =
1,0
00=
100
= 6
,954
d :
x=
bd bd
x=
, a 100
x 6,
954
x =
1,00
0=
695
.4 o
hms.
if a
and
I)
are
equa
l the
res
ista
nce
requ
ired
in th
e rh
eost
at to
eff
ect a
bala
nce
will
be
the
resi
stan
ce o
f th
e lo
op.
If th
e w
ires
are
of
the
sam
ega
uge
and
follo
w th
e sa
me
rout
e th
e re
sist
ance
of
each
may
be
stat
edap
prox
imat
ely
as h
alf
the
mea
sure
d re
sist
ance
.
In th
e ca
se o
f a
sing
le w
ire
test
the
line
is e
arth
ed a
t the
dis
tant
sta
tion
and
join
ed to
C a
t the
test
ing
offi
ce. T
he p
oint
mar
ked
E in
the
Bri
dge
is
also
ear
thed
.T
o en
sure
acc
urac
y th
e te
st s
houl
d be
rep
eate
d w
ith th
eba
ttery
cur
rent
rev
erse
d, a
nd th
e m
ean
of th
e tw
o re
sults
rec
orde
d as
the
true
res
ista
nce
of th
e lin
e.
Insu
latio
n R
esis
tanc
e.-T
he c
onne
ctio
ns n
eces
sary
for
the
mea
sure
men
tof
the
insu
latio
n re
sist
ance
are
sho
wn
in F
ig. 1
18, a
nd a
re s
imila
r to
thos
ere
quir
ed f
or th
e si
ngle
wir
e te
st.
In th
is c
ase
the
line
is d
isco
nnec
ted
atth
e di
stan
t sta
tion,
the
circ
uit b
eing
com
plet
ed th
roug
h th
e po
ints
of
leak
age.
The
insu
latio
n re
sist
ance
, tha
t is
to s
ay, t
he r
esis
tanc
e of
202
NO
TE
S O
N T
EL
EG
RA
PHY
.
the
path
s of
leak
age,
will
now
pro
babl
y be
gre
atly
in e
xces
s of
the
limits
of th
e rh
eost
at, a
nd it
will
con
sequ
ently
be
nece
ssar
y to
mak
e th
e re
sist
ance
of th
e ar
m b
10
or 1
00 ti
mes
gre
ater
than
that
of
a, in
ord
er to
bri
ng th
ein
stru
men
t with
in r
ange
.
Exa
mpl
e 51
.-If
a =
100
b =
1,0
00d
= 7
,600
= in
sula
tion
resi
stan
ce o
f th
e lin
e,th
ena:
b ::
d:x
bd a=
1,00
0x
7,60
0=
76,
000
ohm
s.10
0
The
insu
latio
n re
sist
ance
per
mile
is a
scer
tain
ed b
y m
ultip
lyin
g 76
,000
by
the
num
ber
of m
iles.
Thr
ee -
wir
e L
oop
Tes
ta-W
hen
thre
e w
ires
con
nect
two
stat
ions
the
indi
vidu
al r
esis
tanc
e of
them
may
be
accu
rate
ly d
eter
min
ed b
y ta
king
thre
e lo
op te
sts.
Exa
mpl
e 52
. -L
et x
= th
e re
sist
ance
of
the
firs
t wir
e,Y
=21
Z =
11
Mea
sure
the
resi
stan
ces
ofth
elo
ops
xsu
cces
sive
ly.
12se
cond
wir
e,/1
thir
d w
ire.
y, a
z, a
nd
Supp
ose
xy
= 2
40 o
hms
xz
= 2
60y+
z=
280
By
the
addi
tion
of th
ese
thre
e eq
uatio
ns,
2 (x
yz)
= 7
80 o
hms
z =
390
but y
z =
280
.. x
= 3
90 -
280
= 1
10 o
hms,
= 2
60=
390
- 2
60=
130
ohm
s,an
d x
y =
240
z =
390
- 2
40=
150
ohm
s.T
he th
ree
wir
es x
, y, a
nd z
hav
e 11
0, 1
30, a
nd 1
50 o
hms
resi
stan
cere
spec
tivel
y.
To
Find
the
Dis
tanc
e to
an
Ear
th F
ault.
-Thi
s is
usu
ally
don
e by
mea
nsof
a lo
op te
st, t
he f
aulty
wir
e be
ing
loop
ed to
a k
now
n go
od w
ire.
If th
e
and
xz
Y
If
NO
TE
S O
N T
EL
EG
RA
PHY
.20
3
norm
al r
esis
tanc
e of
the
loop
can
not b
e as
cert
aine
d fr
om e
xist
ing
reco
rds,
an o
rdin
ary
loop
test
, in
whi
ch th
ere
is n
o ea
rth
conn
ectio
n (F
ig 1
17),
shou
ld f
irst
be
mad
e. T
he b
ridg
e is
then
join
ed u
p as
sho
wn
theo
retic
ally
in F
ig. 1
19.
Let
L=
the
resi
stan
ce o
f th
e lo
op.
And
x=
//to
the
faul
t alo
ng o
ne w
ire.
The
n L
-x =
faul
t alo
ng th
e ot
her
wir
e.
The
rhe
osta
t (d)
now
has
the
resi
stan
ce x
add
ed to
it, a
nd th
ear
m o
f th
e pa
ralle
logr
am is
L-x
.
The
fol
low
ing
ratio
may
, the
refo
re, b
e st
ated
:-a
bd+
x:
L-c
e(L
-x)
= b
(d
+ a
)aL
-ax
= b
dbx
bxax
= a
L -
bd
x (a
+ b
) =
aL
- b
daL
bdx
a +
b
four
th
The
res
ista
nces
of
a, b
, d, a
nd L
are
all
know
n, a
nd b
y su
bstit
utio
n th
eva
lue
of x
may
be
dete
rmin
ed.
If a
and
b a
re e
qual
, the
n dx
= L
-xL
-dan
d x
=-2
If th
e re
sist
ance
of
the
sect
ion
of th
e w
ire
(a)
be u
nifo
rm th
roug
hout
,th
e di
stan
ce to
the
faul
t may
be
read
ily a
scer
tain
ed b
y di
vidi
ng th
e va
lue
of a
by
the
know
n m
ileag
e re
sist
ance
of
the
wir
e.Fo
r in
stan
ce, s
uppo
seth
at x
is s
how
n to
be
90 o
hms,
and
the
resi
stan
ce o
f th
e co
nduc
tor
is15
ohm
s pe
r m
ile.
The
dis
tanc
e to
the
faul
t is
six
mile
s.
204
NO
TE
S O
N T
EL
EG
RA
PHY
.
In th
e fo
rego
ing
it ha
s be
en a
ssum
ed th
at th
e re
sist
ance
(x)
to th
e fa
ult
is u
nifo
rm.
It s
omet
imes
hap
pens
, how
ever
, tha
tun
derg
roun
d w
ork,
whi
ch u
sual
ly h
as a
res
ista
nce
of a
bout
24
ohm
spe
r m
ile, i
s in
clud
ld in
this
sec
tion
of th
e lin
e, a
nd it
is, t
here
fore
, nec
essa
ry to
mod
ify
the
calc
ulat
ion
som
ewha
t.If
the
unde
rgro
und
port
ion
is th
ree
mile
s in
leng
th, i
ts r
esis
tanc
e (7
2 oh
ms)
mus
t be
firs
t ded
ucte
d fr
omx,
leav
ing
only
18 o
hms
to b
e ca
lcul
ated
at 1
5 oh
ms
per
mile
.T
he a
eria
l sec
tion
is,
ther
efor
e, 1
i mile
, and
the
tota
l dis
tanc
e to
the
faul
t 4m
iles.
To
Find
the
Dis
tanc
e to
a C
onta
ct.-
The
arra
ngem
ent o
f th
ebr
ill:,
for
this
test
is in
dica
ted
in F
ig. 1
20.
The
arm
b is
now
plu
gged
up
anth
ega
lvan
omet
er jo
ined
bet
wee
n B
and
E.
One
of
the
lines
is e
arth
ed a
t the
dist
ant s
tatio
n, a
nd th
e ot
her,
whi
ch s
erve
sas
a b
atte
ry le
ad a
nd is
use
don
ly to
the
faul
t, is
left
dis
conn
ecte
d.T
he r
esis
tanc
e of
the
eart
hed
line
LIN
E I
Co
nta
ct
LIN
E 7
.dc
s
FIG
120
shou
ld b
e fi
rst a
scer
tain
ed, a
nd it
sho
uld
be n
oted
that
the
circ
uit o
f th
ebr
idge
is c
ompl
eted
thro
ugh
the
eart
h co
nnec
tions
at t
he f
urth
er e
nd o
fth
e lin
e an
d at
E, a
s sh
own
by th
e do
tted
line
in F
ig. 1
20.
Let
L =
the
tota
l res
ista
nce
of th
e ea
rthe
d w
ire,
and
x=
the
resi
stan
ce o
f th
e ea
rthe
d w
ire
up to
the
faul
t;th
en L
-x =
beyo
ndIt
will
, the
refo
re, b
e ap
pare
nt th
at w
ith th
e co
nditi
ons
show
nx
and
L-x
are
two
of th
e re
sist
ance
s fo
rmin
g th
e pa
ralle
logr
am, d
and
a be
ing
the
othe
r tw
o.
The
pro
port
ion
may
, the
refo
re, b
e st
ated
thus
:-d
::
L-x
:x
dx=
aL
-ax
dx +
ax
= a
Lx
(d +
a)
=aL
aLx
=d
+ a
NO
TE
S O
N T
EL
EG
RA
PHY
.20
5
he r
esis
tanc
es o
f a,
d, a
nd L
are
kno
wn,
and
the
ohm
ic d
ista
nce
may
be r
&lil
y ca
lcul
ated
, the
act
ual m
ileag
e be
ing
asce
rtai
ned
in th
e m
anne
rpr
ey o
usly
sho
wn.
To
Find
the
Res
ista
nce
of a
n E
arth
Con
nect
ion.
-The
res
ista
nce
of a
nea
rth
late
sho
uld
not b
e gr
eate
r th
an 1
0 oh
ms,
and
. may
be
asce
rtai
ned
bym
aki g
the
two
follo
win
g te
sts.
In
the
firs
t tes
t a li
ne w
ire,
L1,
is e
arth
ed a
ty
andi
join
ed to
the
brid
ge a
s sh
own
in F
ig. 1
21. T
he "
ear
th"
bein
g te
sted
issh
oiw
ins_
at x
,an
d, h
avin
g ef
fect
ed a
bal
ance
, the
pro
port
ion
of th
e re
sis-
tanc
es
Th
line,
run
a
a:
b:
:d
:y
xbd
=a
(L1
y)ax
(1)
conn
ectio
ns f
or th
e se
cond
test
are
sho
wn
in F
ig. 1
22, a
sec
ond
eart
hed
2, b
eing
use
d fo
r th
e ba
ttery
cir
cuit.
Thi
s lin
e, if
pos
sibl
e, s
houl
dri
ght a
ngle
s to
L1.
In th
is te
st th
e ba
ttery
is r
ever
sed
and
incr
ease
d
FiC
121
.
by a
n ad
ditio
n of
cel
ls, s
o th
at th
e st
reng
thof
the
curr
ent p
assi
ng th
roug
hth
e ea
rth
conn
ectio
n x
may
be
appr
oxim
atel
y eq
ual t
o, a
ndin
the
sam
edi
rect
ion
as in
the
firs
t tes
t.In
this
cas
e le
t the
res
ista
nce
requ
ired
in th
erh
eost
at b
e de
note
d by
r.
The
na
:b
: :r+
x:y
b (r
x) =
a (
L1
y)
Now
sub
trac
t equ
atio
n (2
) fr
om e
quat
ion
(1)
and
bd -
[b
(r +
a)]
= a
(L
1y)
ax -
a (
L1
y)
bd -
br
- bx
= a
x.bd
- b
r =
ax
+ b
x..
x =
a +
bT
he v
alue
of
x m
ay b
e de
term
ined
by
subs
titut
ion.
(2)
206
NO
TE
S O
N T
EL
EG
RA
PHY
.
To
Det
erm
ine
the
Res
ista
nce
of a
Dis
tant
Ear
th-P
late
.-T
he r
esis
ta c
eof
the
eart
h co
nnec
tion
at a
dis
tant
off
ice
may
be
asce
rtai
ned
by m
a in
gsi
ngle
-w
ire
cond
uctiv
ity te
sts
of tw
o of
the
lines
ear
thed
at t
hat o
The
two
lines
sho
uld
then
be
loop
ed in
stea
d of
ear
thed
, and
a lo
op c
on-
duct
ivity
test
mad
e.T
he d
iffe
renc
e be
twee
n th
e su
m o
f th
e tw
o r
sults
obta
ined
with
the
sing
le w
ires
and
the
resi
stan
ce o
f th
e lo
oped
w r
es is
twic
e th
e re
sist
ance
off
ered
by
the
eart
h pl
ate. 1
(
FIG
122
,E
xam
ple
58.-
If th
e in
divi
dual
res
ista
nces
of
two
wir
es e
arth
ed a
t adi
stan
t off
ice
be 3
10 a
nd 3
60 o
hms
resp
ectiv
ely,
and
if a
loop
for
med
by
thes
e tw
o w
ires
be
680
ohm
s, w
hat i
s th
e re
sist
ance
of
the
dist
ant
eart
h co
nnec
tion
?T
he r
esis
tanc
e of
the
two
lines
add
ed to
twic
e th
e re
sist
ance
of
the
" ea
rth
" is
700
ohm
s (3
40 +
360
).T
he r
esis
tanc
e of
the
two
lines
loop
ed, i
.e.,
with
out t
he e
arth
con
nect
ion,
is 6
30 o
hms.
The
refo
re, t
hedi
ffer
ence
bet
wee
n 70
0 oh
ms
and
680
ohm
s di
vide
d by
two
is th
e re
sist
-an
ce o
f th
e ea
rth
plat
e, w
hich
in th
is in
stan
ce is
10 o
hms
and
the
max
imum
res
ista
nce
allo
wed
.T
ests
whi
le a
Cab
le is
bei
ng L
aid.
-It i
s ve
ry im
port
ant t
hat a
fau
ltsh
ould
not
occ
ur w
hile
a c
able
is b
eing
sub
mer
ged
in th
e se
a, a
nd te
sts
are
NO
TE
SO
N T
ELE
GR
AP
HY
.20
7
ap ie
d co
ntin
uous
ly d
urin
gth
e pr
oces
s to
ena
ble
a br
eak
in th
e co
ntin
uity
of t
e co
nduc
tors
or
a fa
ilure
of
insu
latio
nto
be
read
ily d
etec
ted.
If h
e ca
ble
is c
ompo
sed
of a
num
ber
ofco
nduc
tors
they
are
all
join
ed
toge
er to
for
m a
con
tinuo
us c
ondu
ctor
,an
d a
batte
ry o
f on
e or
two
cells
send
a c
urre
nt f
rom
the
ship
thro
ugh
the
seri
es.
Tw
o ga
lvan
omet
ers
are
i elu
ded
in th
e ci
rcui
t, on
e be
ing
at th
e sh
ore
and
the
othe
r at
the
ship
nd
of th
e ca
ble.
Thi
s se
rves
as
a "
cont
inui
ty"
test
, and
a f
ailu
re o
f
the
rren
t ind
icat
es th
at a
fra
ctur
e ha
soc
curr
ed.
If th
ere
is a
n od
d
num
er
of w
ires
in th
e ca
ble,
two
of th
em a
re jo
ined
in "
par
alle
l." S
houl
dei
thof
thes
e be
bro
ken
duri
ng th
e op
erat
ion
of la
ying
, the
res
ista
nce
of
the
ircu
itis
incr
ease
d by
the
failu
reof
the
join
t res
ista
nce,
and
an
imi
diat
e de
crea
se in
the
defl
ectio
n en
sues
.It
is im
pera
tive
that
the
ba,tt
ry
and
galv
anom
eter
s sh
ould
be
wel
l -in
sula
ted
in o
rder
that
the
insu
Lio
n te
st m
ay n
ot b
e af
fect
ed.
Ior
der
that
a c
ontin
uous
insu
latio
n te
st m
aybe
eff
ecte
d, a
n ea
rth
-
con
ecte
d ba
ttery
of
abou
t20
0 ce
lls is
join
ed th
roug
h a
galv
anom
eter
,
FIC
.123
.
spec
ially
dev
ised
for
use
at s
ea,
to th
e ca
ble.
A c
urre
nt is
thus
sen
t fro
m
the
ship
thro
ugh
the
cond
ucto
rs a
ndth
e in
sula
ting
cove
ring
of
the
cabl
e
to th
e se
a.Sh
ould
the
insu
latio
n br
eak
dow
n at
any
poi
nt,
and
thus
affo
rd a
rea
dy e
scap
e fo
r th
e cu
rren
t,th
e de
flec
tion
of th
e ga
lvan
omet
erim
med
iate
ly b
ecom
es a
bnor
mal
,an
d st
eps
are
take
n to
loca
te th
e fa
ult.
The
arr
ange
men
t of
the
batte
ries
and
galv
anom
eter
s fo
r th
ese
test
s is
show
n in
Fig
. 123
.T
o en
able
the
ship
to k
eep
upco
mm
unic
atio
n w
ith th
e sh
ore
the
curr
ent a
pplie
d to
the
cabl
e fo
rth
e "
cont
inui
ty "
test
ispe
riod
ical
ly
reve
rsed
.If
this
rev
ersa
l doe
s no
t tak
e pl
ace
atth
e pr
oper
tim
e, o
r if
the
defl
ectio
n be
com
es u
nste
ady,
com
mun
icat
ion
with
the
ship
is e
stab
lishe
d
by m
eans
of
" sp
eaki
ng "
appa
ratu
s.T
he g
alva
nom
eter
s us
ed f
or th
e"
cont
inui
ty "
test
are
use
d fo
r th
is p
urpo
se,
and
" sp
eaki
ng "
key
s ar
e
brou
ght i
nto
the
circ
uit.
TH
E M
OR
NIN
G T
EST
.
In o
rder
that
the
gene
ral
cond
ition
of
the
mai
n te
legr
aph
and
tele
phon
e lin
es m
aybo
asc
erta
ined
bef
ore
the
actu
alw
ork
of th
e da
y
208
NO
TE
S O
N T
EL
EG
RA
PHY
./1
com
men
ces,
they
are
sub
ject
ed to
an
inge
niou
sly
devi
sed
test
e c
hm
orni
ng b
etw
een
7 an
d 8
o'cl
ock.
Whe
neve
r pr
actic
able
the
tele
g ph
lines
are
loop
ed in
pai
rs, a
nd in
the
case
of
tele
phon
e ci
rcui
ts th
e w
irs
ofth
e lo
op a
re c
onne
cted
at a
con
veni
ent p
oint
for
the
test
s to
be
mad
ero
ma
dist
ant t
estin
g of
fice
.A
t the
off
ice
at w
hich
the
test
is m
ea
curr
ent i
sse
ntth
roug
h a
resi
stan
ce c
oil
of 1
0,00
0 oh
ms
and
one
coil
ofa
diff
eren
tially
wou
ndta
ngen
tga
lvan
omet
er.
Aft
er tr
a-ve
rsin
gth
e lo
op,
the
curr
ent p
asse
s th
roug
h th
e ot
her
galv
ano
eter
coil
and
a se
cond
res
ista
nce
bloc
k of
10,
000
ohm
s, in
suc
h a
dire
tion
that
, if
the
stre
ngth
of
the
curr
ent r
ecei
ved
is e
qual
to th
at s
ent o
ut,
the
galv
anom
eter
nee
dle
will
not
be
defl
ecte
d.If
, how
ever
, an
loss
has
occu
rred
dur
ing
the
pass
age
of th
e cu
rren
t thr
ough
the
loop
the
diff
eren
ce b
etw
een
the
stre
ngth
s of
the
two
curr
ents
will
be
reco
rded
Itsh
ould
be
emph
asis
ed, p
erha
ps, t
hat t
he d
efle
ctio
n re
cord
s ne
ithe
the
stre
ngth
of
the
curr
ent s
ent o
ut n
or th
at o
f th
e cu
rren
t rec
eive
d bu
tsi
mpl
y th
e di
ffer
ence
bet
wee
n th
em.
In f
act t
he d
efle
ctio
n is
a m
ea u
re-
men
t of
the
actu
al lo
ss o
f cu
rren
t whi
ch h
as b
een
sust
aine
d at
the
p in
tsof
leak
age
in th
e lo
op.
In th
e ca
se o
f a
perf
ectly
insu
late
d lo
op th
er w
illbe
no
defl
ectio
n, a
nd th
e ne
arer
this
con
ditio
n is
app
roac
hed
the
sm I
ler
will
be
the
read
ing.
Whe
n th
e lo
op is
uni
form
ly in
sula
ted
the
effe
ct o
f th
ele
akag
e w
il be
equi
vale
nt to
that
of
one
leak
at t
he c
entr
e of
the
line
;th
e re
sist
ance
jof
such
leak
will
be
the
join
t res
ista
nce
of th
e di
stri
bute
d pa
ths
ofle
aka4
e.T
his
cent
ral l
eaka
ge is
term
ed th
e "
resu
ltant
fau
lt."
The
obj
ect o
f th
e tw
o hi
gh r
esis
tanc
e bl
ocks
at t
he e
nds
of th
elo
onis
to p
lace
the
latte
r, w
hich
has
a r
elat
ivel
y lo
wre
sist
ance
, at t
heel
ectr
ical
mid
dle
of th
e ci
rcui
t.A
s th
e lo
op is
the
only
par
t of
the
circ
uit
at w
hich
leak
age
can
occu
r th
e co
nditi
ons
are
such
that
a r
esul
tant
faul
t act
ually
exi
sts,
unl
ess,
of
cour
se, t
he lo
op is
per
fect
ly in
sula
ted.
Whe
n th
ese
cond
ition
s ex
ist t
he m
ean
of th
e su
m o
f th
e "
sent
"an
d"
rece
ived
" c
urre
nts
is e
qual
to th
e cu
rren
t whi
ch w
ould
have
bee
n bo
thse
nt a
nd r
ecei
ved
if n
o le
akag
e ha
d oc
curr
ed, a
nd th
e sa
me
volta
ge h
adbe
enem
ploy
ed.
Infa
ctth
e su
m o
fth
ecu
rren
tsse
ntou
t and
rece
ived
is a
lway
s th
e sa
me,
whe
ther
any
loss
occ
urs
or w
heth
er th
eci
rcui
t is
perf
ectly
insu
late
d, p
rovi
ded
that
no
alte
ratio
n ha
soe
en m
ade
inth
e vo
ltage
.T
his
can
be m
ade
clea
r ar
ithm
etic
ally
.Su
ppos
e th
at a
nel
ectr
o-m
otiv
e fo
rce
of 4
0 vo
lts is
app
lied
to a
per
fect
ly in
sula
ted
circ
uit
of40
0 oh
ms
resi
stan
ce.
The
" p
erfe
ct "
cur
rent
is 1
00 m
illia
mpe
res,
and
this
cur
rent
will
be
both
sen
t and
rec
eive
d.N
ow c
onsi
der
the
sam
eci
rcui
t with
a c
entr
al le
akag
e w
hich
off
ers
100
ohm
s re
sist
ance
.T
hejo
int r
esis
tanc
e fo
rmed
by
the
dist
ant h
alf
ofth
elin
e(2
00 o
hms)
and
the
path
of
leak
age
(100
ohm
s) is
66i
ohm
s, a
nd,
negl
ectin
g th
eba
ttery
, the
tota
l res
ista
nce
is 2
66g
ohm
s.B
y O
hm's
law
it is
fou
nd th
at
NO
TE
S O
N T
EL
EG
RA
PHY
,20
9
a cu
rren
t of
150
mill
iam
pere
s le
aves
the
batte
ry, b
ut a
s tw
o-th
irds
of
ites
cape
s at
the
cent
ral l
eaka
ge o
ne-t
hird
onl
y, o
r 50
mill
iam
pere
s, r
epre
-se
nts
the
rece
ived
cur
rent
.It
will
, the
refo
re, b
e se
en th
at th
e m
ean
of th
e su
m o
f th
e se
nt a
nd r
ecei
ved
curr
ents
is 1
00m
illia
mpe
res,
or
the
sam
e as
the
perf
ect c
urre
nt. S
imila
rly,
if th
e re
sist
ance
of
the
resu
ltant
fau
ltha
d be
en 2
00 o
hms
itm
ay b
e sh
own
that
the
sent
cur
rent
wou
ld h
ave
been
133
1 m
illia
mpe
res
and
the
rece
ived
cur
rent
661
mill
iam
pere
s.In
this
cas
e it
will
be
obse
rved
that
the
mea
n of
the
sum
of
the
two
curr
ents
is a
gain
100
mill
iam
pere
s.T
his
may
be
sum
med
up
by s
tatin
g th
at f
oran
y nu
mbe
r of
mill
iam
pere
s se
nt o
ut in
exc
ess
of th
e pe
rfec
t cur
rent
asi
mila
r nu
mbe
r of
mill
iam
pere
s m
ust b
e de
duct
ed f
rom
the
perf
ect
curr
ent t
o ob
tain
the
rece
ived
cur
rent
.
Supp
ose
that
an
elec
tro-
mot
ive
forc
e, s
uffi
cien
t to
prod
uce
a pe
rfec
tcu
rren
t of
100
mill
iam
pere
s, h
as b
een
appl
ied
to a
cir
cuit
of 2
0,00
0 oh
ms
resi
stan
ce, a
nd th
at th
ere
is a
cen
tral
leak
age
or r
esul
tant
fau
lt in
the
circ
uit w
hich
cau
ses
ade
flec
tion
tobe
regi
ster
ed o
n th
eta
ngen
tga
lvan
omet
er e
quiv
alen
t to
20 m
illia
mpe
res.
From
pre
viou
s ca
lcul
atio
nsit
is e
vide
nt th
at th
e cu
rren
t sen
t out
is 1
00+
= 1
10 m
illia
mpe
res,
and
the
curr
ent r
ecei
ved
is 1
00-2
1p =
90
mill
iam
pere
s.N
ow, f
rom
thes
eda
tath
e re
sist
ance
of th
e pa
thof
leak
age,
whi
chis
the
insu
latio
nre
sist
ance
of
the
who
le li
ne,
may
be
calc
ulat
ed.
The
sen
t cur
rent
aft
ertr
aver
sing
hal
f of
the
circ
uit (
10,0
00 o
hms)
div
ides
at t
he p
oint
of
leak
-ag
e, a
nd 9
0 m
illia
mpe
res
pass
thro
ugh
the
rem
aini
ng 1
0,00
0 oh
ms
ofth
e ci
rcui
t, w
hile
the
20 m
illia
mpe
res
esca
pe th
roug
h th
e fa
ult.
Wha
tth
en, i
s th
e re
sist
ance
of
that
fau
lt ?
The
res
ista
nces
of
the
two
path
sar
e in
inve
rse
prop
ortio
n to
the
curr
ents
pas
sing
thro
ugh
them
.T
here
fore
if=
the
resi
stan
ce o
f ha
lf th
e ci
rcui
tx
=th
e fa
ult
Ci =
the
rece
ived
cur
rent
and
O2=
the
leak
age
curr
ent
R :
x:
:C
,:
10,0
00 :
x:
20:
9020
x =
900
,000
=45
,000
.
The
res
ista
nce
of th
e re
sulta
nt f
ault,
or
the
insu
latio
n re
sist
ance
of
the
circ
uit i
s th
us s
how
n to
be
45,0
00 o
hms.
At a
ll te
stin
g of
fice
s w
here
mor
ning
test
sar
e co
nduc
ted
a pr
oper
lyeq
uipp
edte
stin
gse
tis
prov
ided
for
the
purp
ose
and
fixe
dne
arth
ete
st -
box.
By
mea
nsof
afo
ur -
posi
tion
switc
hth
eco
nnec
-tio
nsar
eal
tere
dto
mee
tal
lre
quir
emen
ts.
Bef
ore
thes
eop
era-
tions
com
men
ceth
eta
ngen
tga
lvan
omet
ersh
ould
bead
just
edby
mea
ns o
f th
e st
anda
rd c
ell,
so th
at b
y us
ing
both
coi
ls a
def
lect
ion
of
210
NO
TE
S O
N T
EL
EG
RA
PHY
.
80 ta
ngen
t div
isio
ns is
equ
ival
ent t
o on
e m
illia
mpe
re.
The
test
ing
batte
ryis
com
pose
d of
fro
m 3
7 to
42
dry
cells
.T
he c
ells
are
soar
rang
edth
at th
e m
inim
um n
umbe
r m
ay b
e ad
ded
toas
requ
ired
.T
he"
cons
tant
" o
f th
e ba
ttery
is ta
ken
by jo
inin
g th
e la
tter
in c
ircu
it w
ithth
e tw
o 10
,000
ohm
blo
cks
and
one
galv
anom
eter
coi
l.A
def
lect
ion
of 1
10di
visi
ons
shou
ld th
en b
e ob
serv
ed, a
nd if
it is
less
than
108
1, c
ells
sho
uld
bead
ded
until
the
requ
ired
def
lect
ion
is o
btai
ned.
As
only
one
coi
lof
the
galv
anom
eter
is e
mpl
oyed
40
divi
sion
s re
pres
ent o
ne m
illia
mpe
re, a
nd th
est
reng
th o
f th
e cu
rren
t is,
ther
efor
e, 2
1 m
illia
mpe
res.
The
ele
ctro
-mot
ive
forc
e of
the
batte
ry m
ay b
e ca
lcul
ated
by
Ohm
's la
w.
E =
0 x
R=
2.7
5 x
20,1
90=
55,
522
5 m
illi -
volts
.
The
res
ista
nce
of 2
0,19
0 oh
ms
is m
ade
up a
s fo
llow
s : T
wo
10,0
00 o
hmbl
ocks
, one
gal
vano
met
er c
oil (
160
ohm
s), a
nd th
e ba
ttery
(30
ohm
s).
10 0
0010
.000
Oir
r)s
40 c
ells
,FI
G.
The
per
fect
cur
rent
in ta
ngen
t div
isio
ns m
ay n
ow b
e ca
lcul
ated
for
any
loop
, the
con
duct
or r
esis
tanc
e of
whi
ch is
kno
wn.
In th
e ca
se o
f a
loop
hav
ing
1,00
0 oh
ms
resi
stan
ce55
,522
-5 x
40
- 10
4 ta
ngen
t div
isio
ns.
The
per
fect
cur
rent
-20
,000
+ 1
,000
+ 3
20 +
30
It s
houl
d he
re b
e no
ted
that
cal
cula
tions
are
mad
e as
thou
gh o
ne c
oil
only
wer
e in
use
.T
he c
urre
nt f
low
ing
thro
ugh
the
leak
is in
dica
ted
inth
e ga
lvan
omet
er b
y th
e ex
cess
of
curr
ent f
low
ing
in o
ne c
oil o
ver
that
inth
e ot
her.
The
res
ulta
nt d
efle
ctio
n is
con
sequ
ently
onl
y th
e ef
fect
of
the
curr
ent i
n on
e co
il.T
he w
hole
res
ista
nce
of th
e ga
lvan
cmet
er, h
owev
er,
has
to b
e de
alt w
ith.
NO
TE
S O
N T
EL
EG
RA
PHY
.21
1
The
con
nect
ions
for
mak
ing
a te
st a
re a
s sh
own
theo
retic
ally
in F
ig. 1
24,
the
switc
h be
ing
in p
ositi
on3.
The
def
lect
ion
then
obs
erve
d is
am
easu
re o
f th
e lo
ss o
f cu
rren
t and
fro
m it
the
resi
stan
ce o
f th
e re
sulta
ntfa
ult,
or th
e in
sula
tion
resi
stan
ce o
f th
e ci
rcui
t, m
ay b
e ca
lcul
ated
.
Whe
n an
abn
orm
al d
efle
ctio
n, in
dica
ting
a sp
ecif
ic f
ault,
is o
bser
ved
whe
n te
stin
g a
loop
, the
sw
itch
is tu
rned
to p
ositi
on 1
.T
he c
urre
nt n
owsp
lits
thro
ugh
the
galv
anom
eter
coi
ls a
nd th
e w
ires
of
the
loop
, the
cir
cuit
bein
g co
mpl
eted
thro
ugh
the
faul
t.If
the
wir
es a
re a
ppro
xim
atel
y eq
ual
in c
ondu
ctor
res
ista
nce,
and
the
dire
ctio
n of
the
defl
ectio
n re
mai
ns u
n-ch
ange
d, th
e w
ire
conn
ecte
d to
the
righ
t-ha
nd te
st -
box
term
inal
is th
e on
eup
on w
hich
the
faul
t exi
sts.
If th
e di
rect
ion
of th
e de
flec
tion
is r
ever
sed,
orit
repr
esen
tsa
" m
inus
" d
efle
ctio
n, th
e ot
her
wir
eis
the
mor
efa
ulty
.If
, how
ever
, no
defl
ectio
n is
obs
erve
d, th
e fa
ult i
s pr
obab
ly n
ear
the
dist
ant,
or lo
opin
g of
fice
, and
may
be
upon
eith
er o
ne w
ire
or th
e ot
her.
In th
ese
circ
umst
ance
s th
e sp
ecif
ic f
ault
is a
ppro
xim
atel
y at
the
cent
re o
fth
e lo
op, a
nd th
e cu
rren
t will
con
sequ
ently
div
ide
equa
lly th
roug
h th
e tw
opa
ths.
Whe
n it
is n
ot p
ossi
ble
to o
btai
n a
loop
for
test
ing
purp
oses
, a s
ingl
elin
e is
ear
thed
thro
ugh
10,1
60 o
hms
at th
e di
stan
t off
ice.
The
rec
ord
book
sho
ws
the
" pe
rfec
t cur
rent
" d
efle
ctio
n an
d th
e de
flec
tion
whi
chw
ould
be
obta
ined
if th
e w
ire
wer
e to
ful
l ear
th in
the
form
of
a fr
actio
n,th
usT
he n
umer
ator
indi
cate
s th
e pe
rfec
t cur
rent
rea
ding
and
the
deno
min
ator
the
full
eart
h re
adin
g.If
a d
efle
ctio
n le
ss, t
han
the
perf
ect
curr
ent d
efle
ctio
n is
rec
orde
d th
e lin
eis
pro
babl
y di
scon
nect
ed.
To
reco
rd th
e ac
tual
loss
in ta
ngen
t div
isio
ns, t
he p
erfe
ct c
urre
nt d
efle
ctio
nis
sub
trac
ted
from
the
actu
al r
eadi
ng a
nd th
e re
-ult
mul
tiplie
d by
two.
If a
rea
ding
of
115
is o
btai
ned
on a
line
, the
per
fect
cur
rent
rea
ding
of
whi
ch is
95,
the
actu
al lo
ss in
tang
ent d
ivis
ions
will
be
2 (1
15-9
5) =
40.
In p
ract
ice
the
test
ing
offi
cer
is s
uppl
ied
with
tabl
es, b
y m
eans
of
whi
chth
e lo
ss r
ecor
ded
in ta
ngen
t div
isio
ns is
rea
dily
con
vert
ed in
to m
egoh
ms
per
mile
.T
he a
ctua
l ins
ulat
ion
resi
stan
ce o
f an
y lin
e sh
ould
not
be
less
than
200
,000
ohm
s pe
r m
ile in
wet
wea
ther
.
'I
192
NO
TE
S O
N T
EL
EG
RA
PHY
.
CH
APT
ER
XX
V.
TE
STS
AN
D M
EA
SUR
EM
EN
TS.
Tel
egra
ph a
nd te
leph
one
circ
uits
are
liab
le to
inte
rrup
tion
from
var
ious
caus
es.
Faul
ts a
rise
in th
e lin
e or
appa
ratu
s w
hich
ren
der
com
mun
ica-
tion
impr
actic
able
.In
ord
er th
at th
e ca
use
of th
est
oppa
ge m
ay b
e lo
cate
dqu
ickl
y al
l cir
cuits
of
any
cons
ider
able
leng
th a
re le
d in
to th
e pr
inci
pal
offi
ces
en r
oute
, and
fac
ilitie
sar
e af
ford
ed w
hich
ena
ble
the
loca
lity
of a
nin
terr
uptio
n to
be
quic
kly
dete
rmin
ed.
At a
ll la
rge
offi
ces
the
wir
es a
re le
d to
a te
st b
ox, f
rom
whi
ch th
e lin
esm
ay b
e co
ntro
lled
and
test
ed, o
r re
-arr
ange
men
ts o
f th
e ap
para
tus
and
,71
116l
178t
o
EE
C
Zis
to
11'4 3
112.
,
lines
mad
e, w
ithou
t los
s of
time.
At o
ffic
es f
rom
whi
cha
larg
e nu
mbe
r of
wir
es r
adia
te th
e w
ires
are
grou
ped
toge
ther
acco
rdin
g to
the
rout
es th
eyfo
llow
.T
here
are
usu
ally
fou
r te
rmin
als
allo
tted
to e
ach
circ
uit,
and
inth
e ca
se o
f te
rmin
ated
line
son
e te
rmin
al is
use
d as
the
eart
hco
nnec
tion.
The
arr
ange
men
t of
a te
st -
box
is s
how
n in
Fig
.11
2, a
nd a
few
of
the
cond
ition
s to
be
met
with
are
indi
cate
d.T
he e
arth
term
inal
isbl
ack,
and
two
circ
uits
are
usua
lly c
onne
cted
with
it.
Lin
es 1
and
13,
whi
chfo
llow
diff
eren
tro
utes
,ar
esh
own
inth
eir
norm
alco
nditi
on,
asal
soar
eth
ose
num
bere
d11
,12
,14
,an
d20
.T
helin
ete
rmin
al is
conn
ecte
d by
mea
ns o
fa
bras
s st
rap
to th
e ad
jace
ntin
stru
men
t ter
min
al, f
rom
whi
cha
lead
run
s to
the
appa
ratu
s.T
he
NO
TE
S O
N T
EL
EG
RA
PHY
.19
3
circ
uit
isco
mpl
eted
by
are
turn
lead
conn
ecte
dto
the
seco
ndin
stru
men
t ter
min
al, w
hich
is s
trap
ped
to th
e ea
rth
conn
ectio
n.L
ino
2is
a "
thro
ugh
" w
ire,
whi
ch r
equi
res
no in
stru
men
ts.
The
dot
ted
line
indi
cate
s th
e co
nnec
tions
mad
e at
the
back
of
the
test
-bo
x.L
ine
3sh
ows
the
conn
ectio
ns f
or "
inte
rmed
iate
" w
orki
ng.
In th
is c
ase
the
retu
rn in
stru
men
t lea
d is
con
nect
ed to
the
" do
wn
" lin
eas
sho
wn.
Lin
e 4
isdi
scon
nect
ed, t
he s
trap
bet
wee
n th
e lin
e an
d in
stru
men
tsha
ving
bee
n re
mov
ed.
Lin
e 5
is"
eart
hed
" di
rect
,th
e in
stru
men
tsbe
ing
cut o
ut o
f th
e ci
rcui
t.L
ine
6 is
cros
sed
with
the
" up
" s
ide
ofnu
mbe
r 8,
and
thos
e nu
mbe
red
7 an
d 10
are
loop
ed to
for
ma
met
allic
circ
uit.
Lin
es 1
5, 1
6, a
nd th
e "
dow
n "
side
of
line
9 sh
ow th
e po
sitio
nof
aff
airs
whe
n a"
dou
ble
" cr
oss
has
been
mad
e;
num
bers
15
and
16ha
ve b
een
cros
sed,
and
aft
erw
ards
a f
urth
er c
ross
was
des
ired
bet
wee
nlin
e 16
and
the
dow
n si
de o
f nu
mbe
r 9.
Lin
es 1
7 an
d 18
are
sho
wn
to b
e"
fork
ed,"
and
are
bei
ng w
orke
d fr
om th
eap
para
tus
usua
lly a
llotte
d to
the
latte
r.L
ine
19 s
how
s ho
w to
" r
ever
se,"
the
eart
h an
d lin
e co
nnec
tions
havi
ng b
een
cros
sed.
The
thre
e ch
ief
caus
es o
f in
terr
uptio
n on
tele
grap
h ci
rcui
ts a
re d
isco
n-ne
ctio
n, e
arth
, and
con
tact
, and
they
may
be
eith
er to
tal,
inte
rmitt
ent,
or p
artia
l.A
tota
l dis
conn
ectio
n m
eans
that
the
cont
inui
ty o
fth
eci
rcui
t has
bee
n en
tirel
y br
oken
.In
term
itten
t dis
conn
ectio
nsre
sult
from
man
y ca
uses
, suc
h as
loos
e co
nnec
tions
of
the
appa
ratu
s te
rmin
als,
or im
perf
ect j
oint
s in
the
line
wir
e, w
hich
mak
e co
ntac
t at i
nter
vals
onl
y.Pa
rtia
l dis
conn
ectio
ns a
re u
sual
ly th
e ou
tcom
e of
the
intr
oduc
tion
ofan
abno
rmal
ly h
igh
resi
stan
ce in
to th
e ci
rcui
t, su
ch a
s w
ould
res
ult f
rom
impr
oper
ly m
ade
join
ts in
the
line
wir
e, lo
ose
term
inal
s or
dir
ty c
onta
ctpo
ints
.E
arth
fau
lts a
re d
ue to
the
cond
ucto
r be
ing
conn
ecte
d to
ear
thso
me
poin
t oth
er th
an th
e ea
rth
plat
es a
t the
end
s of
the
circ
uit.
Ifth
e fa
ult o
ffer
s no
res
ista
nce
it is
sai
d to
be
a "
full
eart
h,"
and
the
fom
ent e
scap
es, i
nste
ad o
f pa
ssin
g to
the
dist
ant o
ffic
e.In
term
itten
tea
rth
faul
ts a
rise
fro
m th
e co
nduc
tor
touc
hing
at i
nter
vals
oth
er b
odie
aw
hich
are
ear
th -
conn
ecte
d an
d ar
ego
od c
ondu
ctor
s.Pa
rtia
lea
rth
resu
lts f
rom
the
cond
ucto
r m
akin
g im
perf
ect c
onta
ct w
ith a
n ea
rth-
coo-
nect
ed c
ondu
ctin
g bo
dy, o
r a
good
con
tact
with
a p
artia
l con
duct
or w
hich
is e
arth
-co
nnec
ted.
Con
tact
res
ults
fro
m tw
o or
mor
e w
ires
bec
omin
g jo
ined
toge
ther
.A
full
cont
act i
mpl
ies
that
the
wir
es a
re in
met
allic
con
tact
, eith
er il
imoo
tor
by m
eans
of
anot
her
wir
e. A
n in
term
itten
t'con
tact
nee
ds in
.pl
oala
tion,
but a
par
tial c
onta
ct is
pro
duce
d by
any
mea
ns w
hich
allo
wa
a po
aloo
the
curr
ent f
rom
one
cir
cuit
topa
ss in
to a
noth
er.
It s
houl
d ho
hor
npo
inte
d ou
t tha
t an
eart
h pl
ate,
whi
ch o
ffer
s a
cons
ider
able
roh
ldat
000,
caus
es a
sem
blan
ce o
f pa
rtia
l con
tact
by
allo
win
g pa
rt o
f I,
ho o
urre
toes
cape
fro
m o
ne c
ircu
it to
the
othe
rs c
onne
cted
with
the
salm
i Pla
ta,
inst
ead
of th
e w
hole
of
it pa
ssin
g di
rect
to e
arth
.
I I
214
NO
TE
S O
N T
EL
EG
RA
PHY
.
be f
orke
d, e
ach
is le
d to
one
of
the
switc
h sp
ring
s of
a g
roup
, and
the
appa
ratu
s co
nnec
tion
is m
ade
by m
eans
of
anot
her
switc
h sp
ring
of
the
EA
RrH
r in
OR
%Z
:cr
;;;:t
moo
mIN
NIM
.1.4
.ros
s:O
R 0
V P
IN a
1,
Tes
t Str
ips.
. . ..
-..4
terf
tedi
atel
fetv
rps,
.
414s
t
1.
*hot
4
...41
1111
111.
1md
.1,1
1101
111r
oC
lfey
a
ieof
tiv S
trip
s.
LT
ear
'al)
3c,
',1::4
417:
411e
iaci
,./ S
at)
(i.f
t PC
ti,r
Tor
0, 7
e re
st)
..4=
=11
J11
ejFI
G. 1
2.6;
App
arat
us I
dled
for
'hits
roie
dial
ls".
307-
470
(lv
.se
for
1i9e
3)
sam
e se
t.T
he li
nes
are
thus
for
ked
and
conn
ecte
d to
the
set o
fap
para
tus
to b
e ut
ilise
d.V
ertic
al te
st -
box
galv
anom
eter
s ar
e pr
ovid
ed, e
ach
ofw
hich
is s
uppl
ied
with
a te
stin
g sw
itch
man
ipul
ated
by
" U
" li
nks.
NO
TE
S O
N T
EL
EG
RA
PHY
.21
5
The
pla
nnin
g ou
t of
the
arra
ngem
ent o
f w
ires
on
a la
rge
test
-bo
x is
asu
bjec
t whi
ch r
equi
res
very
car
eful
con
side
ratio
n.Su
ffic
ient
spa
ce h
as to
be a
llow
ed f
or th
e gr
owth
of
each
" r
oad,
" fo
r, in
asm
uch
as a
ll co
nnec
tions
are
mad
e w
ith s
olde
r, th
e al
tera
tion
of c
onne
ctio
ns a
nd th
e re
arra
ngem
ent
of th
e bo
x ar
e tr
oubl
esom
e an
d te
diou
s op
erat
ions
whi
ch m
ust b
e av
oide
d.
The
sys
tem
of
lead
ing
in w
ires
fro
m th
e st
reet
to th
e in
stru
men
t roo
mha
s re
cent
ly u
nder
gone
a c
ompl
ete
revi
sion
.O
win
g to
the
grea
t str
ides
mad
e in
rec
ent y
ea s
with
ele
ctri
c tr
actio
n, a
nd th
e in
crea
sed
risk
of
fire
or o
ther
inju
ry r
esul
ting
from
con
tact
s be
twee
n te
legr
aph
lines
and
the
cond
ucto
rs u
sed
for
elec
tric
tram
way
s an
d ot
her
elec
tric
inst
alla
tions
, the
met
hod
adop
ted
is a
s fo
llow
s :-
All
wir
es b
efor
e en
teri
ng a
n of
fice
are
led
to a
fus
e -b
ox.
In th
e ca
se o
fun
derg
roun
d lin
es th
e fu
ses
shou
ld b
e pl
aced
at t
he te
rmin
al p
oles
, but
whe
re li
nes
term
inat
e on
ove
rhea
d st
anda
rds
the
fuse
cas
e is
pla
ced
on th
est
anda
rd.
From
the
fuse
cas
es th
e w
ires
are
led
by m
eans
of
lead
cov
ered
cab
les
thro
ugh
iron
tubi
ng, o
r in
the
case
of
a nu
mbe
r of
wir
es ir
on tr
ough
ing,
to li
ghtn
ing
prot
ecto
rs a
nd h
eat c
oils
.
In la
rge
offi
ces
an e
asily
acc
essi
ble
fire
proo
f ch
ambe
r is
bui
lt un
der-
grou
nd o
utsi
de th
e bu
ildin
g, b
ut a
s ne
ar to
itas
pos
sibl
e.T
he v
ario
usun
derg
roun
d ro
utes
term
inat
e in
this
cha
mbe
r, s
o th
at in
the
even
t of
fire
the
mai
n ci
rcui
ts c
an b
e re
adily
join
edup
.Pr
ovis
ion
is a
lso
mad
ehe
re to
eff
ect a
pro
mpt
con
nect
ion
betw
een
mai
n ci
rcui
ts a
nd w
ires
lead
-in
g to
adj
acen
t off
ices
, whe
re th
e tr
affi
c of
the
larg
e to
wns
can
be
imm
e-di
atel
y ta
ken
in h
and.
In th
e ca
se o
f "
thro
ugh
" w
ires
com
mun
icat
ion
can
be q
uick
ly r
esto
red
by c
onne
ctin
g th
e tw
o se
ctio
ns o
f th
e lin
es.
Inth
is c
ham
ber
cabl
e co
nnec
tion
boxe
s ar
e al
so p
rovi
ded
for
term
inat
ing
the
gutta
-per
cha
or p
aper
cov
ered
wir
es.
The
cab
le e
xten
sion
s fr
om th
ese
boxe
s ar
e le
ad c
over
ed a
nd r
un th
roug
h ea
rthe
nwar
e du
cts
to a
n in
ner
cham
ber,
con
stru
cted
in th
e ba
sem
ent o
f th
e bu
ildin
g, a
nd in
whi
ch th
ehe
at c
oil f
ittin
gs a
re p
lace
d.
From
the
heat
coi
ls th
e w
ires
are
led
to th
e te
st -
box
in le
ad c
over
edca
bles
, eac
h co
ntai
ning
127
wir
es r
unni
ng th
roug
h ir
on tr
ough
ing.
The
lead
she
athi
ng o
f th
e ca
bles
is s
olde
red
to le
ad s
trip
s cl
ampe
d to
the
back
of th
e tr
ough
ing
at e
very
few
yar
ds to
ens
ure
the
cabl
es b
eing
imm
ovab
le.
From
the
test
-bo
x th
e w
ires
are
led
in f
ive
or s
even
wir
e le
ad c
over
edca
bles
to th
e in
stru
men
t tab
les,
whe
re th
ey a
re d
istr
ibut
ed f
rom
str
ips
ofco
nnec
ting
tags
.
212
NO
TE
S O
N T
EL
EG
RA
PHY
.
CH
APT
ER
XX
VI.
MO
DE
RN
TE
ST B
OA
RD
S.
The
test
-bo
x us
ed f
or tr
unk
tele
phon
e an
d ju
nctio
n lin
es d
iffe
rs f
rom
the
one
alre
ady
desc
ribe
d.In
stea
d of
term
inal
s an
d br
ass
conn
ectin
gst
raps
, tes
t -ho
les
and
U-s
hape
d lin
ks a
re e
mpl
oyed
.A
s ea
ch c
ircu
itis
am
etal
lic lo
op f
our
test
-ho
les
are
nece
ssar
y,tw
o be
ing
for
the
lines
and
two
for
the
inst
rum
ents
.T
he te
st -
hole
s fo
rm a
squ
are,
the
two
low
er o
nes
bein
g co
nnec
ted
to th
e lin
es a
nd th
e up
per
ones
to th
eap
para
tus
at th
e sw
itch
sect
ion,
as
show
n in
Fig
. 125
.B
y m
eans
of
cros
s -
conn
ectin
g st
rips
ben
eath
the
test
-ho
les
perm
anen
t re
-arr
ange
men
ts o
fth
e lin
es a
nd a
ppar
atus
are
fac
ilita
ted.
Loc
alis
ing
test
s ar
e m
ade
bym
eans
of
a ve
rtic
al g
alva
nom
eter
and
a s
impl
e te
stin
g sw
itch
man
ipul
ated
by "
U "
link
s.T
empo
rary
alte
ratio
ns a
re m
ade
by u
sing
cov
ered
wir
es,
fitte
d at
eac
h en
d w
ith a
spl
it m
etal
plu
g, w
hich
fits
into
the
test
-ho
les.
The
arr
ange
men
t of
the
batte
ry ta
blet
use
d in
con
nect
ion
with
this
boa
rdis
als
o sh
own
in F
ig. 1
25.
The
late
stfo
rmof
test
-bo
xfo
rte
legr
aph
circ
uits
wor
ked
from
Seco
ndar
yba
tteri
esis
a gr
eat
impr
ovem
ent u
pon
the
olde
rty
pe,
whi
ch h
as f
our
term
inal
s an
d tw
o br
ass
conn
ectin
g st
raps
for
eac
hci
rcui
t.In
the
new
for
m s
witc
h sp
ring
s an
d te
st -
hole
s ar
e em
ploy
ed,
and
cros
s -c
onne
ctin
g st
rips
are
fitte
d at
the
foot
of th
e te
stca
se.
The
arr
ange
men
t of
the
switc
h sp
ring
s w
ill b
e re
adily
und
erst
ood
byre
fere
nce
to F
ig. 1
26.
Nor
mal
ly th
ere
are
no c
onne
ctio
ns a
t the
fro
ntof
the
test
-bo
x,bu
t, w
hen
lines
are
take
nfo
rte
stin
g pu
rpos
es o
rre
-ar
rang
emen
ts a
re m
ade,
the
alte
ratio
ns a
re e
ffec
ted
by m
eans
ofco
vere
d w
ires
, whi
ch a
re te
rmin
ated
in c
onne
ctin
g pl
ugs.
The
latte
r fi
tin
to th
e te
st -
hole
s an
d es
tabl
ish
conn
ectio
n w
ith th
e ou
ter
switc
h sp
ring
s.T
he li
ne is
join
ed to
one
set
of
oute
r sw
itch
spri
ngs
and
the
appa
ratu
sw
ith th
e ot
her,
the
circ
uit b
eing
com
plet
ed th
roug
h th
e in
ner
spri
ngs,
whi
ch a
re e
lect
rica
lly c
onne
cted
.It
will
thus
be
seen
that
ope
ratio
ns a
reve
ry m
uch
sim
plif
ied,
as
by th
e ac
t of
inse
rtin
g a
plug
the
oute
r sp
ring
sar
e di
scon
nect
ed f
rom
the
inne
r on
es.
By
inse
rtin
g a
plug
into
the
line
test
-ho
le th
e ap
para
tus
is a
utom
atic
ally
cut
off
, and
, sim
ilarl
y, th
e lin
e is
disc
onne
cted
fro
m th
e ap
para
tus
whe
n a
plug
is in
sert
ed in
the
test
-ho
leal
lotte
d to
the
latte
r.T
he e
arth
con
nect
ion
is e
ffec
ted
at th
e in
stru
men
tta
ble,
and
this
resu
ltsin
asa
ving
of w
ire,
ason
e le
adon
lyis
nece
ssar
y be
twee
n th
e te
st -
box
and
the
appa
ratu
s.T
he c
ondu
ctor
s fo
rth
e in
stru
men
t lea
ds a
re m
ade
up in
to c
able
s, w
hich
con
tain
fiv
e or
sev
enw
ires
insu
late
d w
ith a
mix
ture
of
silk
and
cot
ton.
From
the
fore
goin
git
will
be
notic
ed th
at it
is n
ot p
ossi
ble
for
two
lines
to b
e co
nnec
ted
and
NO
TE
S O
N T
EL
EG
RA
PHY
.21
3
the
appa
ratu
s re
mai
n in
the
circ
uit.
Thi
s, h
owev
er, i
s pr
ovid
ed f
or b
yte
rmin
atin
g a
few
of
the
sets
of
appa
ratu
s at
the
test
-bo
x th
roug
h an
addi
tiona
l sw
itch
spri
ng. S
witc
h sp
ring
s us
ed f
or th
ispu
rpos
e ar
e gr
oupe
d
Tliu
ffit
BA
TT
ER
Y 'F
AU
LT
.
13 a
te -
FIG
.125
.to
geth
er a
nd la
belle
d "
inte
rmed
iate
ret
urns
."In
ord
er th
at tw
o or
mor
ew
ires
may
be
" fo
rked
" a
nd w
orke
das
a d
ivid
ed c
ircu
it, s
ets
of s
wite
lisp
ring
sar
epr
ovid
ed.
The
y ar
ela
belle
d"
grou
ping
," a
ndal
lth
eou
ter
spri
ngs
of e
ach
set a
re c
onne
cted
toge
ther
.R
espe
ctin
g th
e lin
os to
22N
OT
ES
ON
TE
LE
GR
APH
Y.
MA
GN
ET
IC U
NIT
S.
The
re a
re tw
o m
agne
tic u
nits
, viz
.: (a
) T
he u
nit m
agne
tic p
ole
and
(...
the
mag
netic
fie
ld o
f un
it in
tens
ity.
(a)
A u
nit m
agne
tic p
ole
is o
no o
f su
ch s
tren
gth
that
whe
n pl
aced
at a
dist
ance
of
one
cent
imet
re in
air
fro
m a
sim
ilar
pole
of
equa
l str
engt
hre
pels
it w
ith a
for
ce*
of o
ne d
yne.
(b)
The
mag
netic
fie
ld o
f un
it in
tens
ity e
xert
s a
forc
e of
one
dyn
e on
a un
it m
agne
tic p
ole.
EL
EC
TR
ICA
L U
NIT
S.
Tw
o sy
stem
s of
ele
ctri
cal u
nits
, ter
med
the
elec
tro-
stat
ic a
nd e
lect
ro-
mag
netic
uni
ts, h
ave
been
dev
ised
in c
onne
ctio
n w
ith th
e fu
ndam
enta
l and
deri
ved
units
.T
he e
lect
ro-s
tatic
sys
tem
, whi
ch d
eals
with
ele
ctri
city
ina
stat
e of
res
t, is
bas
ed u
pon
the
repu
lsio
n an
d at
trac
tion
betw
een
elec
tric
char
ges,
and
incl
udes
the
units
of
quan
tity,
pot
entia
l, an
d ca
paci
ty.
The
ele
ctro
-mag
netic
sys
tem
is u
sed
in c
onne
ctio
n w
ith c
urre
nt e
lect
rici
ty.
In th
is s
yste
m a
re in
clud
ed th
e un
its o
f cu
rren
t, re
sist
ance
, ele
ctro
-mot
ivo
forc
e, a
nd q
uant
ity.
The
uni
ts o
f th
ese
two
syst
ems
are
freq
uent
ly te
rmed
" a
bsol
ute
" un
its,
and
are
eith
er to
o sm
all o
r to
o la
rge
for
ordi
nary
wor
k.A
pra
ctic
alsy
stem
, how
ever
, has
bee
n de
vise
d by
a C
omm
ittee
of
the
Bri
tish
Ass
ocia
tion,
the
units
of
whi
ch b
ear
cert
ain
fixe
d ra
tios
to th
e "
abso
lute
"un
its.
PRA
CT
ICA
L U
NIT
S.
The
uni
t of
elec
tro-
mot
ive
forc
e, o
r un
it di
ffer
ence
of
pote
ntia
l, is
cal
led
the
volt,
and
is a
bout
the
elec
tro-
mot
ive
forc
e of
a D
anie
ll ce
ll.T
hem
illi -
volt
is o
ne -
thou
sand
th p
art o
f a
volt.
The
uni
t of
resi
stan
ce is
the
ohm
, and
is th
e re
sist
ance
of
a co
lum
n of
mer
cury
106
cen
timet
res
(abo
ut 3
Vt.)
long
, one
squ
are
mill
imet
re (
abou
tnt
h of
a s
quar
e in
ch)
in c
ross
sec
tion,
at 0
0 ce
ntig
rade
.T
he m
egoh
m is
one
mill
ion
ohm
s, a
nd th
e m
icro
hm o
ne -
mill
iont
h pa
rt o
f an
ohm
.T
he u
nit o
f cu
rren
t is
the
ampe
re, a
nd is
the
curr
ent p
rodu
ced
byan
ele
ctro
-mot
ive
forc
e of
one
vol
t thr
ough
a r
esis
tanc
e of
one
ohm
.T
he m
illia
mpe
reis
one
-tho
usan
dth
part
ofan
am
pere
, and
is th
ecu
rren
t pro
duce
d by
an
elec
tro-
mot
ive
forc
e of
one
vol
t thr
ough
1,0
00oh
ms
resi
stan
ce.
The
uni
t of
quan
tity
is th
e co
ulom
b, a
nd is
that
qua
ntity
of
elec
tric
ityw
hich
flo
ws
in a
cur
rent
of
one
ampe
re la
stin
g on
e se
cond
.T
he u
nit o
f ca
paci
ty is
the
fara
d. A
con
dens
er o
f on
e fa
rad
capa
city
will
con
tain
one
cou
lom
b of
ele
ctri
city
with
a d
iffe
renc
e of
pot
entia
l of
one
volt
betw
een
the
plat
es.
The
mic
ro -
fara
d is
one
-m
illio
nth
part
of
afa
rad.
Not
e.-C
are
shou
ld b
e ta
ken
to d
istin
guis
h be
twee
n th
e pr
efix
es "
mill
i "an
d "
mic
ro."
" M
illi "
sig
nifi
es "
one
-th
ousa
ndth
par
t of,
" an
d "m
icro
""
one
-mill
iont
h pa
rt o
f."
NO
TE
s O
N 'T
EL
EG
RA
PHY
.23
OH
M'S
LA
W.
It h
as a
lrea
dy b
een
show
n th
at a
cur
rent
of
elec
tric
ity is
the
outc
ome
oftw
o po
ints
at d
iffe
rent
ele
ctri
cal p
oten
tials
bei
ng jo
ined
by
a co
nduc
tor.
The
str
engt
h of
the
curr
ent d
epen
ds e
ntir
ely
upon
the
diff
eren
ce o
fpo
tent
ial '
betw
een
the
two
poin
ts, a
nd th
e re
sist
ance
of
the
path
pro
vied
dfo
r it.
So lo
ng a
s th
e di
ffer
ence
of
pote
ntia
l and
the
resi
stan
ce r
emai
nco
nsta
nt, a
ste
ady
curr
ent w
ill b
e m
aint
aine
d. A
ny v
aria
tion
in th
e el
ectr
o-m
otiv
e fo
rce
or th
e re
sist
ance
will
pro
duce
a v
aria
tion
in th
e st
reng
thof
the
curr
ent.
The
fun
ctio
n of
the
batte
ry is
to p
rovi
de th
e ne
cess
ary
diff
eren
ce o
f po
tent
ial t
o pr
omot
e th
e fl
ow o
f cu
rren
t.O
hm's
law
sta
tes
that
the
stre
ngth
of
a cu
rren
t is
dire
ctly
pro
port
iona
lto
the
elec
tro-
mot
ive
forc
e, a
nd in
vers
ely
prop
ortio
nal
toth
eto
tal
resi
stan
ce o
f th
e ci
rcui
t.In
oth
er w
ords
, the
cur
rent
will
incr
ease
in s
tren
gth
in d
irec
t pro
port
ion
to a
n in
crea
se in
the
elec
tro-
mot
ive
forc
e, a
nd w
ill d
ecre
ase
with
an
incr
ease
in th
e re
sist
ance
of
the
circ
uit.
Ohm
's la
w m
ay, t
here
fore
, be
stat
ed th
us :-
Cur
rent
=E
lect
ro-m
otiv
e fo
rce
Res
ista
nce
The
se th
ree
quan
titie
s sh
ould
be
expr
esse
d in
term
s of
thei
r un
its, a
ndth
e be
ginn
er s
houl
d be
car
eful
to n
ote
that
, with
the
elec
tro-
mot
ive
forc
egi
ven
in v
olts
and
the
resi
stan
ce in
ohm
s, th
e cu
rren
t will
be
in a
mpe
res,
not m
illia
mpe
res.
The
sym
bols
gen
eral
ly u
sed
to d
enot
e cu
rren
t, el
ectr
o-m
otiv
e fo
rce,
and
resi
stan
ce a
re r
espe
ctiv
ely
C.,
E.,
and
R.,
so th
at th
e la
w m
ay b
e br
iefl
yst
ated
as
-C
The
refo
reE
And
R
=C
x
C
Bea
ring
in m
ind
thes
e th
ree
sim
ple
form
ulae
, if
any
two
of th
e qu
antit
ies
be g
iven
the
thir
d ca
n al
way
s be
asc
erta
ined
.E
xam
ple
1.-W
ith a
n el
ectr
o-m
otiv
e fo
rce
of f
our
volts
and
a r
esis
tanc
eof
two
ohm
s, w
hat i
s th
e st
reng
th o
f th
e cu
rren
t ?
C
and,
sub
stitu
ting
the
valu
es o
f th
e kn
own
quan
titie
s fo
r th
eir
rela
tive
sym
bols
-0
=4 2
C =
2 a
mpe
res.
24A
OZ
ES
ON
TE
LE
GR
APH
Y.
Exa
mpl
e 2.
-Wha
t is
the
stre
ngth
of
the
curr
ent p
rodu
ced
by a
n el
ectr
o-m
otiv
e fo
rce
of to
n vo
lts th
roug
h a
resi
stan
ce o
f 20
ohm
s?
C =
Ti'
0 =
1° 20 1
= -
ampe
re2
or C
=1
x 1,
000
= 5
00 m
illia
mpe
res.
2
As
ther
e ar
e 1,
000
mill
iam
pere
s in
one
am
pere
, to
expr
ess
the
answ
er in
mill
iam
pere
s th
e nu
mbe
r of
am
pere
s sh
ould
be
mul
tiplie
d by
1,0
00.
Exa
mpl
e 3.
-Wha
t ele
ctro
-mot
ive
forc
e is
req
uire
d to
pro
duce
a c
urre
ntof
2 a
mpe
res
thro
ugh
a re
sist
ance
of
2 oh
ms
?E
=O
xR=
2 x
2=
4 v
olts
.E
xam
ple
4.-I
f a
curr
ent o
f 50
0 m
illia
mpe
res
is o
btai
ned
thro
ugh
are
sist
ance
of
20 o
hms,
wha
t ele
ctro
-mot
ive
forc
e is
use
d ?
E=
CxR x
-2-
=1
20
= 1
0 vo
lts.
Exa
mpl
e 5.
-Wha
t is
the
resi
stan
ce o
f a
circ
uit i
n w
hich
a c
urre
nt o
f2
ampe
res
is p
rodu
ced
by a
n el
ectr
o-m
otiv
e fo
rce
of 4
vol
ts?
a =
0 4O
MM
.Elf
2
=2
ohm
s.E
xam
ple
6.-I
f a
curr
ent o
f ha
lf a
n am
pere
is p
rodu
ced
by a
n el
ectr
o-m
otiv
e fo
rce
of 1
0 vo
lts, w
hat i
s th
e re
sist
ance
of
the
circ
uit ?
C 10
=x
102
11
20 o
hms.
NO
TE
S O
N T
EL
EG
RA
PHY
.25
Not
e.-T
he s
tude
nt s
houl
d no
teth
e re
latio
n w
hich
exi
sts
betw
een
exam
ples
1, 3
, and
5, a
nd b
etw
een
2, 4
, and
6.
Whe
n a
circ
uit i
s m
ade
up o
f a
num
ber
of s
epar
ate
resi
stan
ces
join
edto
geth
er in
ser
ies,
the
tota
l res
ista
nce
is f
ound
by
addi
ng th
e in
divi
dual
resi
stan
ces
toge
ther
.C
are
shou
ld b
e ta
ken
to in
clud
e th
e re
sist
ance
of
the
batte
ry.
Exa
mpl
e 7.
-A b
atte
ry h
avin
g an
ele
ctro
-mot
ive
forc
e of
20
volts
and
an
inte
rnal
res
ista
nce
of 2
5 oh
ms,
is jo
ined
to a
cir
cuit
com
pose
d of
a g
alva
no-
met
er o
f 75
ohm
s re
sist
ance
and
a w
ire
of 4
00 o
hms
resi
stan
ce.
Wha
tcu
rren
t flo
ws
thro
ugh
the
galv
anom
eter
. ?W
here
C =
Cur
rent
in a
mpe
res.
E =
Ele
ctro
-mot
ive
forc
e of
the
batte
ry.
R =
Res
ista
nce
of th
e w
ire.
G =
Res
ista
nce
of th
e ga
lvan
omet
er.
and
r =
Res
ista
nce
of th
e ba
ttev.
C =
R +
G +
r20
400
+ 7
5 +
25
20 500
1 - am
pere
25
orC
=x
1,00
0 =
40
mill
iam
pere
s.25
Exa
mpl
e 8.
-Wha
t is
the
resi
stan
ce o
f a
batte
ry h
avin
g an
ele
ctro
-m
otiv
e fo
rce
of 2
0 vo
lts if
a c
urre
nt o
f 40
mill
iam
pere
s is
pro
duce
d th
roug
ha
tota
l ext
erna
l res
ista
nce
of 4
75 o
hms
?
The
40
mill
iam
pere
s m
ust n
ow b
e di
vide
d by
1,0
00 to
bri
ng th
atqu
antit
y to
the
prop
er u
nit,
viz.
, am
pere
s.1
40 m
il Im
pere
s =
40=
ampe
re.
1000
25
In th
is c
ase
let R
= to
tal e
xter
nal r
esis
tanc
e
then
C =
R +
r1
20
2547
5 +
rC
ross
mul
tiply
ing
475
+ r
= 5
00r
= 5
00 -
475
= 2
5 oh
ms.
20N
OT
ES
ON
TE
LE
GR
APH
Y.
Nam
e.Po
si-
tivo
plat
e.E
xciti
ngfl
uid.
Neg
ativ
epl
ate.
Dep
olar
isin
gag
ent.
Ele
ctro
-m
otiv
efo
rce
per
cell.
App
roxi
mat
ere
sist
ance
per
cell.
Dan
iell
....
Loc
lanc
ho ..
Bic
hrom
ate.
.
Zin
c
Zin
c
Zin
c
Sulp
huri
cac
id(H
2SO
4)S
a 1
a m
-L
eoni
a°(N
H4C
I)Su
lphu
ric
acid
(H2S
O4)
Cop
per
(Cu)
Car
bon
(C)
Car
bon
(C)
S u
1 p
k a
t e o
fc:
pper
(UuS
O4)
Pero
xide
o f
man
gane
se(M
n02)
Mix
ture
of
bi-
chro
mat
e of
of p
otas
h(K
2 O
r, 0
, )&
dilu
te s
ul-
phur
ic a
cid
(H2S
O4)
,w
hich
for
ms
chro
mic
acid
(11,
0r04
),th
e de
pola
r-is
ing
agen
t.
1'08
vol
t
1.5
volt.
2 vo
lts..
Var
ies
from
3to
10oh
ms.
Var
ies
from
.25
to4
ohm
s.2
ohm
s.
It w
ill b
e no
ticed
that
in e
ach
case
zin
c is
use
d as
the
posi
tive
plat
e.T
ho r
easo
n fo
r th
is w
ill b
e re
adily
und
erst
ood
by a
ref
eren
ce to
the
cont
act
seri
es in
whi
ch z
inc,
is s
how
n to
be
posi
tive
to a
ll th
e ot
her
bodi
es g
iven
.In
the
Loc
lanc
ho a
nd D
ichr
omat
e ce
lls c
arbo
n is
the
nega
tive
elem
ent,
but i
n th
e D
anie
ll ce
ll th
e ne
gativ
e pl
ate
is c
oppe
r.In
the
latte
r ca
se th
edi
ffer
ence
of
pote
ntia
l bet
wee
n th
e pl
ates
is n
ot s
o gr
eat a
s in
the
othe
rtw
o, b
ut b
y th
e ch
emic
al a
ctio
n w
hich
take
s pl
ace
in4h
e D
anie
ll ce
ll th
ede
posi
tion
of c
oppe
r up
on th
e ne
gativ
e pl
ate
wou
ld r
ende
r ca
rbon
un-
suita
ble.
The
dif
fere
nce
in th
e el
ectr
o-m
otiv
e fo
rce
ofth
e L
ecla
nchO
and
bich
rom
ate
cells
, not
with
stan
ding
the
sim
ilari
tyof
the
plat
es,
is b
roug
ht a
bout
by
the
othe
r in
gred
ient
s us
ed in
thei
r co
nstr
uctio
n.T
ho o
bjec
tof
the
depo
lari
sing
agen
tin
eac
h ca
seis
to a
rres
t the
hydr
ogen
evo
lved
and
pro
duce
a h
arm
less
com
poun
d.In
the
Dan
iell
cell
sulp
huri
c ac
idis
for
med
by
the
chem
ical
com
bina
tion
of th
e hy
drog
enw
ith th
e su
lphi
on o
f th
e su
lpha
te o
f co
pper
, pur
e co
pper
bei
ng d
epos
ited
on th
e co
pper
plat
e.In
the
Lec
lanc
he a
nd B
ichr
omat
e ce
lls th
ede
pola
risi
ng a
gent
s ha
ve a
larg
e pr
opor
tion
of o
xyge
n in
thei
r co
mpo
sitio
n,w
hich
, whe
n ch
emic
ally
uni
ted
with
the
evol
ved
hydr
ogen
, for
ms
wat
er.
NO
TE
S O
N T
EL
EG
RA
PHY
.21
CH
APT
ER
III
.
UN
ITS.
To
expr
ess
the
mag
nitu
de o
f an
y ph
ysic
al q
uant
ity it
is n
eces
sary
tom
ake
use
of a
uni
t of
mea
sure
men
t. T
o st
ate
the
wei
ght o
f a
body
a u
nit
of w
eigh
t mus
t be
empl
oyed
.W
eigh
t may
be
expr
esse
d as
so
man
ypo
unds
or
tons
, and
it w
ould
be
usel
ess
to a
ttem
pt to
con
vey
the
idea
of
the
wei
ght o
f an
y su
bsta
nce,
say
cop
per,
by
usin
g th
e te
rm "
ten
copp
er."
A u
nit o
f w
eigh
t mus
t be
used
, and
the
expr
essi
on a
men
d to
" to
n4\
,po
unds
of
copp
er "
or
" te
n to
ns o
f co
pper
," b
efor
e an
y id
ea o
f th
e w
eigh
tca
n be
com
preh
ende
d.A
ll ph
ysic
al q
uant
ities
mus
t be
expr
esse
d as
the
prod
uct o
f a
unit
and
a nu
mbe
r.T
hus
" te
n to
ns"
expr
esse
s a
defi
nite
wei
ght,
" fi
ve s
econ
ds"
a de
fini
te ti
me,
and
" f
ifte
en y
ards
" a
defi
nite
leng
th.
Ele
ctri
city
,ho
wev
er, c
anno
t be
mea
sure
d by
any
of
the
ordi
nary
stan
dard
s of
mea
sure
men
t, as
it d
oes
not p
osse
ss th
e at
trib
utes
whi
chen
able
oth
er p
hysi
cal q
uant
ities
to b
e st
ated
in te
rms
of a
uni
t.T
hepr
esen
ce o
f el
ectr
icity
can
onl
y be
dem
onst
rate
d by
the
effe
ct p
rodu
ced,
by
mea
ns o
f w
hich
a s
yste
m o
f el
ectr
ical
uni
ts h
as b
een
devi
sed.
FUN
DA
ME
NT
AL
UN
ITS.
The
fun
dam
enta
l sys
tem
of
units
has
bee
n al
mos
t uni
vers
ally
ado
pted
by s
cien
tists
, and
is s
o ca
lled
beca
use
upon
it o
ther
sys
tem
s of
sci
entif
icm
easu
rem
ents
are
bas
ed.
It is
fre
quen
tly c
alle
d th
e C
. G. S
. sys
tem
fro
mth
e in
itial
lette
rs o
f th
e un
its e
mpl
oyed
, viz
. :-
Cen
timet
re,
Gra
mm
e,Se
cond
.
The
cen
timet
re is
the
unit
of le
ngth
, and
is r
epre
sent
ed b
y ab
out t
wo
-fi
fths
of
an in
ch. T
he g
ram
me
is th
e un
it of
mas
s, a
nd is
abo
ut 1
5i g
rain
s;th
e la
st u
nit,
whi
ch is
the
unit
of ti
me,
bei
ng th
e or
dina
ry s
econ
d.Fr
om th
ese
thre
e un
its o
ther
s, c
alle
d "
deri
ved"
uni
ts, a
re o
btai
ned.
The
dyn
e is
the
unit
of f
orce
, or
that
for
ce w
hich
, act
ing
upon
a m
ass
ofon
e gr
amm
e m
oves
it a
dis
tanc
e of
one
cen
timet
rein
one
sec
ond.
The
erg
is th
e un
it of
wor
k or
ene
rgy,
and
is th
e am
ount
of
wor
k do
ne,
or e
nerg
y ex
pend
ed, a
gain
st a
for
ce o
f on
e dy
ne th
roug
h a
dist
ance
of
one
cent
imet
re.
The
re a
re o
ther
der
ived
uni
ts, v
iz.,
the
unit
of w
eigh
t, th
e un
it of
velo
city
, the
uni
t of
acce
lera
tion,
and
the
unit
of h
eat,
but i
t is
thou
ght
they
do
not c
all f
or d
efin
ition
in th
ese
note
s.
28N
OT
ES
ON
TE
LE
GR
APH
Y.
By
Ohm
's la
w- 0
(n x
r)R
4 x
20
-(4
x 2
) +
80
=8tota
l ole
ctro
-mot
ive
forc
eto
tal r
esis
tanc
en
x e
16
C =
ampe
re, o
r 50
0 m
illia
mpe
res.
To
asce
rtai
n th
e nu
mbe
r of
cel
ls w
hich
sho
uld
be jo
ined
in s
erie
s in
orde
r to
pro
duce
a c
erta
in c
urre
nt th
roug
h a
give
n ex
tern
al r
esis
tanc
e,
n_
014
e -0
rn
for
C =
nre
Cro
ss m
ultip
lyin
g ne=
Cnr
+ O
Rne
-Cnr
= C
Rn
CR
-e-C
rE
xam
ple
11.-
How
man
y ce
lls jo
ined
in s
erie
s m
ust b
e em
ploy
ed to
send
a c
urre
nt o
f 50
0 m
illia
mpe
res
thro
ugh
an e
xter
nal r
esis
tanc
e of
8 oh
ms,
if e
ach
cell
has
a re
sist
ance
of
2 oh
ms
and
an e
lect
ro-m
otiv
e fo
rce
of 2
vol
ts ?
(See
exa
mpl
e 10
.) nC
Re
-C r
x 8
n=
22._
()n
=4
cells
.
NO
TE
.-E
xam
ple
10 s
how
s th
is r
esul
t to
be c
orre
ct.
Ver
y lit
tle a
dvan
tage
is g
aine
d by
join
ing
cells
in s
erie
sto
a lo
w e
xter
nal
resi
stan
ce.
Und
er th
ese
circ
umst
ance
s an
y in
crea
se in
the
num
ber
of c
ells
resu
lts in
the
tota
l res
ista
nce
bein
g in
crea
sed
in v
ery
near
ly th
e sa
me
prop
ortio
n as
the
elec
tro-
mot
ive
forc
e.C
onse
quen
tly th
e cu
rren
t is
not a
ppre
ciab
ly a
ugm
ente
d.If
, how
ever
, it i
s de
sire
d to
sen
d a
curr
ent
thro
ugh
a hi
gh e
xter
nal r
esis
tanc
e, th
e ce
lls s
houl
d be
join
ed in
ser
ies,
and
the
elec
tro-
mot
ive
forc
e w
ill r
ise
in p
ropo
rtio
n to
the
num
ber
of c
ells
add
ed ;
but t
he a
dditi
onal
bat
tery
res
ista
nce
will
not
mat
eria
lly a
ffec
t the
tota
lre
sist
ance
.
NO
TE
S O
N T
EL
EG
RA
PHY
.26
The
ele
otro
-mot
ive
forc
e of
a c
ell d
epen
ds e
ntir
ely
upon
the
mat
eria
ls o
fw
hich
the
cell
is c
ompo
sed,
and
is in
depe
nden
t of
its s
ize.
The
res
ista
nce,
how
ever
, var
ies
with
the
dim
ensi
ons
of th
e ce
ll an
d al
so w
ith th
e bo
dies
of w
hich
the
cell
is c
ompo
sed.
The
res
ista
nce
of a
con
duct
or v
arie
s di
rect
ly a
s th
e le
ngth
and
inve
rsel
yas
the
area
of
the
cros
s se
ctio
n of
the
cond
ucto
r. T
hat i
s to
say,
a lo
ng w
ire
will
hav
e a
grea
ter
resi
stan
ce th
an a
sho
rt o
ne, p
rovi
ded
that
the
two
are
iden
tical
in o
ther
res
pect
s, a
nd,
of tw
o w
ires
of
the
sam
e le
ngth
and
mat
eria
l, th
e th
icke
r w
ill h
ave
the
smal
ler
resi
stan
ce.
The
sam
e m
ay b
esa
id o
f ba
tteri
es.
If c
ells
are
join
ed to
geth
er in
ser
ies
the
resi
stan
cein
crea
ses
with
eve
ry c
ell a
dded
.It
is s
omet
imes
nec
essa
ry, h
owev
er, i
nor
der
toge
tgo
od r
esul
ts f
rom
a g
iven
num
ber
ofce
lls,
tojo
inth
em u
p in
suc
h a
man
ner
as to
pro
duce
a lo
w b
atte
ry r
esis
tanc
e.Im
agin
e ho
w th
e re
sist
ance
of
a co
mbi
natio
n of
two
cells
is a
ffec
ted
if,
inst
ead
of jo
inin
g th
em in
ser
ies,
the
two
posi
tive
plat
es a
nd th
e tw
one
gativ
epl
ates
are
join
ed to
geth
er.
The
two
cells
are
pra
ctic
ally
mad
e in
to o
ne,
havi
ng it
s ar
ea o
f cr
oss
sect
ion
doub
le th
at o
f on
e of
the
orig
inal
cel
ls.
The
pla
tes
of th
e co
mbi
natio
n ar
e tw
ice
as la
rge
as th
ose
ofon
e ce
ll, a
ndth
e pa
th f
or th
e cu
rren
t thr
ough
the
liqui
d is
dou
bled
inar
ea o
f cr
oss
sect
ion,
with
out i
ncre
asin
g th
e di
stan
ce b
etw
een
the
plat
es.
The
res
ist-
ance
is, t
here
fore
, hal
f th
at o
f on
e ce
ll.T
he c
ells
are
now
sai
d to
be
join
ed in
par
alle
l arc
, or
quan
tity.
Fig.
15
show
s, d
iagr
amat
ical
ly, t
wo
cells
join
ed in
ser
ies,
and
Fig
. 16
two
cells
arr
ange
d in
par
alle
l arc
.It
has
alr
eady
bee
n ex
plai
ned
that
the
elec
tro-
mot
ive
forc
e of
two
cells
join
ed in
ser
ies
is tw
ice
that
ofon
ece
ll, a
nd a
littl
e co
nsid
erat
ion
will
sho
w h
ow th
e el
ectr
o-m
otiv
e fo
rce
isaf
fect
ed b
y th
e qu
antit
y m
etho
d of
gro
upin
g. A
s th
ere
are
prac
tical
ly o
nly
two
plat
es in
the
latte
r ea
se, o
ne p
ositi
ve a
nd o
ne n
egat
ive,
the
sim
ilar
plat
es o
f th
e tw
o ce
lls b
eing
con
nect
ed, t
he e
lect
ro-m
otiv
e fo
rce
is o
nly
that
of
one
cell.
1461
11_,
.'s o
n tk
i.toR
APH
I,
The
re is
, how
ever
, an
inte
rmed
iate
met
hod
betw
een
the
tw6
syst
ems
ofgr
oupi
ng a
lrea
dy d
escr
ibed
.A
num
ber
of c
ells
can
be
arra
nged
to f
orm
seve
ral r
ows,
and
the
row
s jo
ined
for
qua
ntity
.Fo
r in
stan
ce, t
wel
ve c
ells
may
be
join
ed u
p in
thre
e ro
ws
of f
our
cells
eac
h.T
he f
our
cells
in e
ach
row
are
join
ed in
ser
ies,
and
the
thre
e ro
ws
arra
nged
in q
uant
ity. F
ig. 1
7 sh
ows
the
arra
ngem
ent d
iagr
amat
ical
ly. B
y
'FIG
. 17
this
met
hod
the
tota
l bat
tery
res
ista
nce
will
be
the
resi
stan
ce o
f on
e ce
llm
ultip
lied
by th
e nu
mbe
r of
cel
ls in
eac
h ro
w, d
ivid
ed b
y th
e nu
mbe
r of
row
s.T
his
will
be
appa
rent
fro
m w
hat h
as a
lrea
dy b
een
expl
aine
d in
conn
ectio
n w
ith c
ells
join
ed e
ither
all
in s
erie
s or
all
in q
uant
ity.
The
resi
stan
ce in
crea
ses
with
the
num
ber
ofce
llsjo
ined
inse
ries
, and
dim
inis
hes
as th
e pa
th f
or th
e cu
rren
t inc
reas
es in
are
a 03
cro
ss s
ectio
n.T
he g
reat
er th
e nu
mbe
r of
row
s of
cel
ls a
rran
ged
the
smw
ill b
e th
ere
sist
ance
.T
he e
lect
ro-m
otiv
e fo
rce
of a
com
bina
tion
of c
ells
arr
,1ed
par
tly in
seri
es a
nd p
artly
abr
east
dep
ends
ent
irel
y up
on th
e nu
mbe
r of
cel
ls in
each
row
.T
hus,
if tw
elve
cel
ls a
re a
rran
ged
in tw
o ro
ws
of s
ix c
ells
eac
hth
e el
ectr
o-m
otiv
e fo
rce
of th
e co
mbi
natio
n w
ill b
e si
x tim
es th
at o
f on
ece
ll.If
they
are
arr
ange
d in
thre
e ro
ws
of f
our
cells
eac
h th
e el
ectr
o-m
otiv
e fo
rce
will
be
four
tim
es th
at o
f on
e ce
ll.W
here
n =
the
num
ber
of c
ells
in a
row
,m
= th
e nu
mbe
r of
row
s of
cel
ls,
e =
the
elec
tro-
mot
ive
forc
e pe
r ce
ll,an
d r
= th
e re
sist
ance
per
cel
l,th
e to
tal e
lect
ro-m
otiv
e fo
rce
----
n x
ean
d th
e to
tal r
esis
tanc
e =
n X
r
m
NO
TE
S O
N T
EL
EG
RA
PHY
.31
Exa
mpl
e 12
.-Fo
ur c
ells
, eac
h ha
ving
an
elec
tro-
mot
ive
forc
e of
1i v
olt
and
a re
sist
ance
of
2 oh
ms,
are
join
ed u
p in
par
alle
l arc
.W
hat c
urre
ntw
ill th
ey p
rodu
ce th
roug
h an
ext
erna
l res
ista
nce
of 4
ohm
s ?
Let
m =
the
num
ber
of c
ells
join
ed in
qua
ntity
,T
hen
Ce
Rm
+ 4
1i
=A
am
pere
, or
334
mill
iam
pere
s.
Exa
mpl
e 13
.-A
bat
tery
of
16 c
ells
is jo
ined
up
in 4
row
s of
4 c
ells
eac
hto
sen
d a
curr
ent t
hrou
gh a
n ex
tern
al r
esis
tanc
e of
30
ohm
s.It
eac
h ce
llha
s an
ele
ctro
-mot
ive
forc
e of
2 v
olts
and
a r
esis
tanc
e of
2 o
hms,
wha
t will
be th
e st
reng
th o
f th
e cu
rren
t ?
Whe
re C
e r R n
and
m
= c
urre
nt in
am
pere
s,=
ele
ctro
-mot
ive
forc
e pe
r ce
ll,=
res
ista
nce
per
cell,
= e
xter
nal r
esis
tanc
e,=
num
ber
of c
ells
in a
row
,=
num
ber
of r
ows
of c
ells
,th
e to
tal e
lect
ro-m
otiv
e fo
rce
= n
x e
n x
ran
d th
e to
tal b
atte
ry r
esis
tanc
e =
And
sub
stitu
ting,
C
nl n
x e
n x
r+
4 x
24
x 2
+ 3
04
8 + 3
04
=32 1
=4
ampe
re, o
r 25
0 m
illia
mpe
res.
32N
OT
ES
ON
TE
LE
GR
APH
Y.
Exa
mpl
e 14
.-If
100
cel
ls, e
ach
havi
ng a
n el
ectr
o-m
otiv
e fo
rce
of 1
.5vo
lt an
d a
resi
stan
ce o
f 3
ohm
s, a
re jo
ined
up
20 in
ser
ies
and
five
abr
east
to a
n ex
tern
al r
esis
tanc
e of
48
ohm
s, w
hat i
s th
e st
reng
th o
f th
e cu
rren
t ?
=n
xnx
r+B
m 20 x
1.5
20 x
3+
48
5
30
60+
48
5 30 60
= 1
ampe
re,
2 or 5
00 m
illia
mpe
res.
Exa
mpl
e /5
.-10
0 ce
lls, e
ach
havi
ng a
res
ista
nce
of 3
ohm
s, a
re jo
ined
up 2
0 in
ser
ies
and
five
abr
east
to a
n ex
tern
al r
esis
tanc
e of
48
ohm
s. W
hat
Is th
e ol
eotr
o-m
otiv
e fo
rce
per
cell
if a
cur
rent
of
half
an
ampe
reis
prod
uced
?
Cro
ss m
ultip
lyin
g,
C -
n x
en.
x r
Rnl
1=
20 x
e
220
x-r
5
120
n=
..+.
60
40 e
= 6
0 60 400
1.5
volt.
.E;r
ampl
e la
.-A
cur
rent
of
500
mill
iam
pere
s is
pro
duce
d by
a b
atte
ryof
100
0on
e w
hen
join
ed u
p 20
In
Her
iee
and
five
abr
east
.If
the
elec
tro-
mot
ive
forc
e of
mel
t eel
! la
1.5
vol
t and
the
exte
rnal
res
ista
nce
48 o
hms.
wha
t Is
the
reid
stan
ee p
er c
ell ?
NO
TE
S O
X T
EL
EG
RA
PHY
.
=n
x e
n X
r
111
1=
20 x
1.5
222
0+
48
130
20 r
+ ,
no
Cro
ss m
ultip
lyin
g,
20r
48 =
60
04
r =
60
- 48
r =
3 o
hms.
83
Exa
mpl
e 17
.-T
hrou
gh w
hat e
xter
nal r
esis
tanc
e w
ould
100
cel
ls, e
ach
havi
ng a
n el
ectr
o-m
otiv
e fo
rce
of 1
.5 v
olt a
nd a
res
ista
nce
of 3
ohm
s, s
end
a cu
rren
t of
500
mill
iam
pere
s if
the
cells
wer
e ar
rang
ed 2
0 in
ser
ies
and
five
abre
ast?
Cx
en
xr
"777
"R
1=
20 x
1.5
275
71-1
Cro
ss m
ultip
lyin
g,12
+ I
I =
CO
= 6
0 -
12 =
48
ohm
s.T
he m
axim
um c
urre
nt is
obt
aine
d fr
om a
bat
tery
whe
n th
e in
tern
alre
sist
ance
is e
qual
to th
e ex
tern
al r
esis
tanc
e.If
by
an a
rran
gem
ent o
f th
ece
lls th
e ba
ttery
res
ista
nce
can
be m
ade
equa
l to
the
resi
stan
ce o
f th
eci
rcui
t out
side
the
batte
ry, O
len
the
curr
ent o
btai
ned
will
be
grea
ter
byth
is a
rran
gem
ent t
han
by a
ny o
ther
met
hod
of g
roup
ing.
If th
e tw
ore
sist
ance
s ca
nnot
be
mad
e eq
ual,
then
the
arra
ngem
ent w
hich
mos
tne
arly
app
roac
hes
this
con
ditio
n w
ill b
e th
e on
e w
hich
will
pro
duce
the
grea
test
cur
rent
.W
ith a
hig
h ex
tern
al r
esis
tanc
e th
e ce
lls s
houl
d be
join
ed in
ser
ies.
It w
ill b
e se
en th
at b
y th
e se
ries
met
hod
the
batte
ryw
ill h
ave
a gr
eate
r re
sist
ance
than
by
any
arra
ngem
ent o
f th
e ce
llsab
reas
t.W
ith a
low
ext
erna
l res
ista
nce
a su
itabl
e m
etho
d of
gro
upin
gth
e ce
lls c
an b
e de
vise
d to
pro
duce
a r
esis
tanc
e of
the
batte
ry e
qual
to, o
rne
arly
equ
al to
, the
res
ista
nce
of th
e ex
tern
al p
art o
f th
e ci
rcui
t.
34N
OT
ES
ON
TE
LE
GR
APH
Y.
To
obta
in th
e m
axim
um c
urre
nt f
rom
a g
iven
num
ber
of c
ells
thro
ugh
a gi
ven
exte
rnal
res
ista
nce
The
num
ber
of c
ells
arr
ange
d in
ser
ies
=
whe
re T
= th
e to
tal n
umbe
r of
cel
ls,
= th
e ex
tern
al r
esis
tanc
e,an
dr
= th
e in
tern
al r
esis
tanc
e pe
r ce
ll.
Exa
mpl
e 18
.-H
ow w
ould
you
arr
ange
60
cells
, eac
h ce
ll ha
ving
an
elec
tro-
mot
ive
forc
e of
2 v
olts
and
a r
esis
tanc
e of
2 o
hms,
to s
end
the
stro
nges
t pos
sibl
e cu
rren
t thr
ough
an
exte
rnal
res
ista
nce
of 7
i ohm
s ?
The
num
ber
of c
ells
in s
erie
s=V
-T
x R
r
V60
x
The
cel
ls s
houl
d be
arr
ange
d in
fou
r
By
this
met
hod
of g
roup
ing
-
C
=2
W;
2
=V
225
=15
row
s of
15
cells
eac
h.
n x
en
x r
+ R
15 x
215
x'2
+ 7
i4 30
771-
2 am
pere
s.T
he in
tern
alre
sist
ance
is 7
i ohm
s, o
r th
e sa
me
as th
e ex
tern
alre
sist
ance
.
To
prov
e th
at th
e m
axim
um c
urre
nt is
obt
aine
dby
this
arra
nge-
men
t, th
e cu
rren
t sho
uld
be c
ompa
red
with
(a)
that
obt
aine
d by
grou
ping
the
cells
with
a s
mal
ler
num
ber
of r
ows
and
mor
e ce
lls in
seri
es, a
nd (
5)th
e cu
rren
t pro
duce
d by
the
arra
ngem
ent o
f a
grea
ter
num
ber
ofro
ws
and
less
cel
ls in
ser
ies.
NO
TE
S O
N T
EL
EG
RA
PHY
.35
(a)
20 in
ser
ies
and
3 ab
reas
t.n
x e
x r
Rm 20
x 2
(b)
12 in
ser
ies
and
5 ab
reas
t.
_n
x e
n x
rR
12 x
220
x 2
12 x
2+7
5
40=
24 wom
ns.
-13
-I-
7i-
44-
+ 7
i13
4 am
pere
.=
1am
pere
.W
ith th
e ba
ttery
res
ista
nce
13k
ohm
s. th
e cu
rren
t is
114
ampe
re.
ff9
/4
,I
7)
It w
ill b
e se
en, t
here
fore
, tha
t with
the
batte
ry r
esis
tanc
e eq
ual t
o th
eex
tern
al r
esis
tanc
e th
e cu
rren
t obt
aine
d is
gre
ater
than
by
any
othe
rar
rang
emen
t of
the
cells
.
2am
pere
s.11
i am
pere
.
It m
ay b
e of
inte
rest
to s
ee h
ow th
e fo
rmul
a V
.x
R,r
is o
btai
ned.
T
Who
re R
= th
e ex
tern
al r
esis
tanc
e,T
= th
e to
tal n
umbe
r of
cel
ls,
r =
the
resi
stan
ce p
er c
ell,
n =
the
num
ber
of c
ells
in s
erie
s,m
= th
e nu
mbe
r of
row
s of
cel
ls,
the
batte
ry r
esis
tanc
e =
n x
rm
to o
btai
n th
e m
axim
um c
urre
ntH
=nx
rbu
t, as
T =
n x
mm
_n
and,
sub
stitu
ting
this
val
ue o
f m
in e
quat
ion
(1)
nxr n
R =
n2x
rT
Cro
ss m
ultip
lyin
g,n2
xr=
TxR
T x
R r
kirl
=n2
=
(1)
NO
TE
S O
N T
EL
EG
RA
PHY
.
A o
onsI
dera
tion
of th
e fo
llow
ing
will
sho
w m
athe
mat
ical
ly w
hy th
em
axin
iuut
ow
-re
nt is
obt
aine
d w
hen
the
batte
ry r
esis
tanc
e eq
uals
the
uxL
erni
Ll r
esis
tanc
e.el
0
IIl'
It11
1
e n
m--
--nr
±m
Re
m
- V
in R
)22,
\/n m
r R
:loor
any
arr
ange
men
t of
a gi
ven
num
ber
of c
ells
the
quan
tity
n m
isco
nsta
nt, a
s it
repr
esen
ts th
e to
tal n
umbe
r of
cel
ls.
The
num
erat
or(e
n in
), in
the
fina
l val
ue o
f C
sho
wn
abov
e, is
ther
efor
eal
so c
onst
ant,
and
the
stre
ngth
of
the
curr
ent w
ill d
epen
d up
on th
e de
nom
inat
or.
Her
e w
eha
ve2,
\/0 m
r R
als
o a
cons
tant
qua
ntity
.If
, the
n, b
y an
arr
ange
men
t
of th
e ce
lls w
e ca
n m
ake
(V11
m lt
l2 =
0, t
he d
enom
inat
or
will
be
as s
mal
l as
poss
ible
, and
, as
a co
nseq
uenc
e, th
e cu
rren
t will
be th
e
grea
test
obt
aina
ble.
Thi
s w
ill b
e so
whe
nnr
= m
RR
n r
Or
i.e.,
whe
n th
e ex
tern
al r
esis
tanc
e eq
uals
the
inte
rnal
res
ista
nce.
Exa
mpl
e 19
.-H
ow m
any
cells
, eac
h ha
ving
an
elec
tro-
mot
ive
forc
e of
2 vo
lts a
nd a
n in
tern
al r
esis
tanc
e of
3 o
hms,
mus
t be
empl
oyed
tose
nd a
curr
ent o
f 1
ampe
re th
roug
h an
ext
erna
l res
ista
nce
of 1
0 oh
ms?
An
exam
inat
ion
of th
is q
uest
ion
reve
als
the
fact
that
with
the
cells
arra
nged
in s
erie
s it
is im
poss
ible
to o
btai
n a
curr
ent o
f 1
ampe
re. E
ven
if th
e ce
lls a
re jo
ined
up
with
out a
ny a
ppre
ciab
le e
xter
nal
resi
stan
ce -
the
tota
l res
ista
nce
in o
hms
mus
t alw
ays
be n
umer
ical
ly g
reat
erth
an th
e to
tal
elec
tro-
mot
ive
forc
e in
vol
ts.
Neg
lect
ing
the
exte
rnal
res
ista
nce,
one
cel
l,or
100
cel
ls jo
ined
in s
erie
s, c
anno
t pro
duce
mor
eth
an tw
o-th
irds
of
an
ampe
re.
Allo
win
g fo
r th
e ex
tern
al r
esis
tanc
e, th
e cu
rren
t,of
cou
rse,
will
be le
ss th
an tw
o-th
irds
of
an a
mpe
re.
If th
e ce
lls a
re a
ll jo
ined
in p
aral
lel a
rc, t
heel
ectr
o-m
otiv
e fo
rce
will
be
2 vo
lts.
With
an
exte
rnal
res
ista
nce
of 1
0 oh
ms
and
a ne
glig
ible
inte
rnal
resi
stan
ce th
e cu
rren
t will
be
only
one
-fi
fth
of a
n am
pere
.It
is, t
here
fore
, app
aren
t at t
he o
utse
t tha
tth
e ce
lls m
ust n
eith
er b
ear
rang
ed a
ll in
ser
ies
nor
all a
brea
st.
How
then
sho
uld
the
cells
be
grou
ped
?C 1
=
n X
0
(1)
NO
TE
S O
N T
EL
EG
RA
PHY
.37
To
obta
in a
max
imum
cur
rent
fro
m a
giv
en n
umbe
r of
cel
ls th
e in
tern
alre
sist
ance
of
the
batte
ry s
houl
d eq
ual t
he e
xter
nal r
esis
tanc
e.Fr
om th
isit
follo
ws
that
, in
orde
r to
pro
duce
a g
iven
cur
rent
fro
ma
min
imum
num
ber
of c
ells
, the
sam
e co
nditi
ons
shou
ld e
xist
.
The
refo
re, f
rom
equ
atio
n (1
),n
x 8
= 1
011
1
n x
3= 1
0 x
mn
x 3
and
m=
10
Subs
titut
e th
is v
alue
of
m in
equ
atio
n (1
).
1 =
n x
2
1
and,
sin
ce m
n x
3x
310
n x
210
+ 1
02
x n
= 2
0n
= 1
0 n x
310
10 x
3
+ 1
0
(2)
(2)
= M
I110
101.
51M
IMN
D
10
= 3
but t
he to
tal n
umbe
r of
cel
ls, T
= n
x m
T =
10
x 3
= 3
0A
NSW
ER
. -T
hirt
y ce
lls s
houl
d be
use
d, jo
ined
10
in s
erie
s an
d 3
abre
ast.
It s
omet
imes
hap
pens
, mer
e of
ten
by a
ccid
ent t
han
desi
gn, t
hat c
ells
are
join
ed u
p in
opp
ositi
on.
Inst
ead
of th
e ce
lls b
eing
gro
uped
as
inth
e se
ries
met
hod,
one
por
tion
of th
em is
rev
erse
d, s
o th
at o
ne s
ectio
n of
the
batte
ry te
nds
to s
end
a cu
rren
t in
one
dire
ctio
n, a
nd th
e ot
her
port
ion
in th
e op
posi
te d
irec
tion.
In a
cas
e of
this
kin
d th
e re
sulta
nt c
urre
nt is
foun
d by
mak
ing
calc
ulat
ions
whi
ch a
llow
for
the
diff
eren
ce b
etw
een
the
elec
tro-
mot
ive
forc
e of
the
two
sect
ions
.A
s al
l the
cel
ls a
re in
the
path
of th
e cu
rren
t, th
e re
sist
ance
of
the
who
le o
f th
em m
ust b
e in
clud
ed w
hen
calc
ulat
ing
the
tota
l res
ista
nce.
Exa
mpl
e 20
.-T
en c
ells
are
join
ed u
p so
that
six
of
them
tend
to s
end
acu
rren
t in
one
dire
ctio
n, a
nd th
e re
mai
nder
in th
e op
posi
te d
irec
tion.
Ifea
ch o
f th
e te
n ce
lls h
as a
res
ista
nce
of 3
ohm
s an
d an
ele
ctro
-mot
ive
2fN
OT
ES
ON
TE
LE
GR
APH
Y.
Exa
mpl
e 9.
-A b
atte
ry h
avin
ga
resi
stan
ce o
f 25
ohm
s is
join
edto
aci
rcui
tof
475
ohm
s re
sist
ance
and
prod
uces
a c
urre
nt o
f 40
mill
i -am
p\ r
os.
Wha
t is
the
elec
tro-
mot
ive
forc
eof
the
batte
ry ?
CR
r1 25
475
+ 2
5
25 E
= 5
00E
=20
vol
ts.
Cro
ss m
ultip
lyin
g
27
CH
APT
ER
IV
.
TH
E G
RO
UPI
NG
OF
CE
LL
S.
A v
olta
icce
llis
usua
lly s
how
n, d
iagr
amat
ical
ly,
tiptw
o V
ertic
alpa
ralle
l lin
es ;
a sh
ort t
hick
line
to d
enot
e th
e po
sitiv
e pl
ate,
and
a th
inlin
e to
rep
rese
nt th
e ne
gativ
e pl
ate.
A b
atte
ry o
f ce
lls is
dep
icte
d as
anu
mbe
r of
thes
e pa
irs
join
ed in
a r
ow, t
he n
egat
ive
plat
e of
one
cell
bein
gjo
ined
to th
e po
sitiv
e pl
ate
of th
e ne
xt, a
nd s
o on
,un
til a
ll th
e ce
llsco
mpr
isin
g th
e ba
ttery
are
con
nect
ed.
A p
ositi
ve p
late
at o
ne e
nd w
ad a
nega
tive
plat
e at
the
othe
r en
d ar
e le
ft f
ree,
and
form
the
poin
ts o
fbon
-ne
ctio
n to
the
exte
rnal
par
t of
the
circ
uit.
(Fig
. 15.
)
no. I
s.T
he a
bove
arr
ange
men
t is
term
ed jo
inin
g th
ece
lls "
in s
erie
s."
The
res
ist-
ance
of
a ba
ttery
of
this
des
crip
tion
is th
e re
sist
ance
of
one
cell
mul
tiplie
dby
the
num
ber
of c
ells
em
ploy
ed.
As
an il
lust
ratio
n, ta
ke f
our
bich
rom
ate
cells
, eac
h ha
ving
a r
esis
tanc
e of
two
ohm
s,an
d co
nnec
t the
m in
ser
ies
;th
e to
tal r
esis
tanc
e of
the
batte
ry w
ill b
efo
ur ti
mes
that
of
one
cell,
viz
.,
eigh
t ohm
s.T
he e
lect
ro-m
otiv
e fo
rce
of s
uch
a ba
ttery
will
als
o be
fou
r
times
that
of
one
cell.
Ass
umin
g ea
ch c
ell t
o ha
ve a
n el
ectr
o-m
otiv
efo
rce
of tw
o vo
lts, t
hen
the
tota
l dif
fere
nce
of p
oten
tial b
etw
een
the
ter-
min
als
of th
e ba
ttery
will
be
eigh
t vol
ts.
Whe
re th
e nu
mbe
r of
cel
ls jo
ined
in s
erie
sis
rep
rese
nted
by
n, th
ere
sist
ance
per
cel
l by
r, a
nd th
e el
ectr
o-m
otiv
efo
rce
per
cell
bye,
then
The
tota
l bat
tery
res
ista
nce
= n
x r
,an
d th
e to
tal e
lect
ro-m
otiv
e fo
rce
= n
x e
.
Exa
mpl
e /0
. --F
our
cells
join
ed in
seri
es a
re c
onne
cted
to a
wir
e ha
ving
a re
sist
ance
of
eigh
t ohm
s.If
eac
h ce
ll ha
s an
ele
ctro
-mot
ive
forc
e of
two
volts
and
a r
esis
tanc
e of
two
ohm
s, w
hat i
sth
e st
reng
th o
f th
e cu
rren
t 2
Whe
re C
= th
e cu
rren
t in
ampe
res,
e =
the
elec
tro-
mot
ive
forc
e pe
r ce
ll,r
= th
e re
sist
ance
per
cel
l,It
= th
e ex
tern
al r
esis
tanc
e,an
d n
= th
e nu
mbe
r of
cel
ls jo
ined
in s
erie
s.
40N
OT
ES
ON
TE
LE
GR
APH
Y.
I n
Fig.
18
imag
ine
the
circ
le A
to b
e th
e cr
oss
sect
ion
of a
wir
e, a
ndth
e cu
rren
t to
be f
low
ing
from
the
read
er in
to th
e pl
ane
of th
e pa
per.
A
swim
mer
wou
ld d
ive
into
the
pape
r he
ad f
orem
ost,
and,
upo
n tu
rnin
g to
fam
the
mag
net,
or a
ny o
ne o
f th
e fi
lings
in th
is c
ase,
the
nort
h -s
eeki
ngpo
lo w
ould
be
upon
the
side
of
his
left
han
d, a
s in
dica
ted.
A f
ree
nort
h -
seek
ing
pole
, wer
e it
poss
ible
to p
rodu
ce a
sin
gle
pole
mag
net,
wou
ldro
tate
aro
und
the
wir
e in
the
dire
ctio
n sh
own
by th
e ar
row
s, w
hile
a f
ree
sout
h -s
eeki
ng p
olo
wou
ld, o
f co
urse
, be
urge
d in
an
oppo
site
way
.Fr
om th
e fo
rego
ing,
then
, it w
ill b
e re
adily
und
erst
ood
that
a f
reel
ysu
spen
ded
mag
netic
nee
dle
may
be
defl
ecte
d fr
om it
s no
rmal
pos
ition
inth
e m
agne
tic m
erid
ian,
if b
roug
ht w
ithin
the
mag
netic
fie
ld s
urro
undi
nga
wir
e co
nduc
ting
a cu
rren
t of
elec
tric
ity.
Oer
sted
disc
over
edth
isph
enom
enal
actio
n up
ona
susp
ende
dm
agne
tic n
eedl
e, a
nd th
e co
nstr
uctio
n of
gal
vano
scop
es a
nd g
alva
nom
eter
s,to
res
pect
ivel
y in
dica
te th
e pr
esen
ce o
f el
ectr
ic c
urre
nts
and
to m
easu
reth
em, i
s ba
sed
upon
this
kno
wle
dge.
The
impo
rtan
t poi
nt to
he
give
n pr
omin
ence
at t
his
junc
ture
, how
ever
,is
the
effe
ct o
f th
is e
lect
ro-m
agne
tism
whe
n th
e w
ire
is w
ound
into
asp
iral
or
helix
.(F
ig. 1
9.)
FIG
19,
With
a g
iven
cur
rent
eac
h tu
rn o
f th
e w
ire
incr
ease
s th
e m
agne
ticef
fect
of
the
spir
al.
Thi
s ef
fect
, rou
ghly
spe
akin
g, is
pro
port
iona
l to
the
prod
uct o
f th
e cu
rren
t in
amp6
res
and
the
num
ber
of tu
rns
of w
ire
in th
eco
il.In
oth
er w
ords
the
mag
netic
eff
ect i
ncre
ases
as
the"
am
pere
turn
s."
The
hel
ix, o
r so
leno
id a
s it
is s
omet
imes
cal
led,
is a
mag
net o
nly
so lo
ngas
the
curr
ent f
low
s.It
s m
agne
tic li
nes
of f
orce
are
sim
ilar
to th
ose
abou
t an
ordi
nary
bar
mag
net.
Out
side
the
coil
they
for
m c
lose
d cu
rves
,w
hile
insi
de th
ey r
un p
aral
lel t
o its
leng
th a
nd p
rotr
ude
at th
e en
ds.
A s
olen
oid
poss
esse
s th
e po
wer
s of
attr
actio
n an
d re
puls
ion,
but
its
pola
rity
dep
ends
upo
n tw
o th
ings
, (a)
the
dire
ctio
n in
whi
ch th
e co
il, o
rhe
lix,
is w
ound
-whe
ther
rig
ht-h
ande
dly
or le
ft-h
ande
dly-
and
(b)
the
dire
ctio
n of
the
curr
ent.(
...W
ith a
thor
ough
kno
wle
dge
of A
mpe
re's
rul
e,ho
wev
er, n
o di
ffic
ulty
will
be
expe
rien
ced
in f
indi
ng th
e po
lari
ty o
f a
sole
noid
whe
n th
e di
rect
ion
of th
e cu
rren
t is
know
n.Fu
rthe
r, lo
okin
g at
a kn
own
sout
h -s
eeki
ng o
r no
rth
-see
king
pol
e (F
ig. 2
0) th
e di
rect
ion
of th
em
agne
tisin
g cu
rren
t can
be
av .e
rtai
ned.
Whe
n lo
okin
g at
a s
outh
-se
ekin
gpo
le th
e cu
rren
t tra
vers
ing
the
spir
al c
ircu
late
s in
the
dire
ctio
n of
the
hand
s
NO
TE
S O
N T
EL
EG
RA
PHY
.41
of a
clo
ck, b
ut w
hen
look
ing
at a
nor
th -
seek
ing
pole
the
mag
netis
ing
curr
ent c
ircu
late
s in
the
oppo
site
dir
ectio
n.T
his
rule
is c
orre
ct e
ither
for
a r
ight
-han
ded
or a
left
-han
ded
helix
.
Fla
7,'.
PER
ME
AB
ILIT
Y A
ND
SU
SCE
PTIB
ILIT
Y.
Perm
eabi
lity,
or
the
co -
effi
cien
t of
mag
netic
indu
ctio
n, m
ay b
e de
fine
das
the
ratio
of
mag
netic
con
duct
ivity
exi
stin
g be
twee
n va
riou
s su
bsta
nces
and
air
from
a g
iven
mag
netis
ing
forc
e.T
he n
umbe
r of
line
s of
for
ce p
ersq
uare
cen
timet
re in
any
sub
stan
ce d
eter
min
es it
s de
gree
of
perm
eabi
lity.
In a
ir a
nd n
on-m
agne
tic b
odie
s th
e nu
mbe
r of
line
s of
for
ce is
ver
ysm
all,
whi
le in
mag
netic
sub
stan
ces,
suc
h as
iron
, the
num
ber
of li
nes
ofm
agne
tic in
duct
ion
is r
elat
ivel
y la
rge.
It w
ill b
e se
en, t
here
fore
, tha
t by
plac
ing
a so
ft ir
on c
ore
into
a h
elix
,a
muc
h gr
eate
r nu
mbe
r of
line
s of
mag
netic
indu
ctio
n w
ill b
e co
ncen
trat
edin
the
iron
than
was
for
mer
ly c
onta
ined
in th
e ai
r sp
ace
;co
nseq
uent
lyth
e m
agne
tic s
tren
gth
of s
uch
a co
mbi
natio
n w
ill b
e m
uch
grea
ter
than
that
of
the
sole
noid
.Su
ppos
e a
cert
ain
mag
netis
ing
forc
e cr
eate
d, s
ay, 5
0 lin
es o
f fo
rce
per
squa
re c
entim
etre
in a
ir, t
he s
ame
forc
e w
ould
pro
duce
abo
ut 1
6,00
0 lin
esof
for
ce p
er s
quar
e ce
ntim
etre
in s
oft i
ron.
The
per
mea
bilit
y of
the
latte
r,th
eref
ore,
wou
ld b
e 32
0 tim
es g
reat
er th
an th
e fo
rmer
.T
he n
umbe
r of
line
s of
for
ce p
er s
quar
e ce
ntim
etre
in a
ir is
usu
ally
deno
ted
by th
e le
tter
H, a
nd th
e nu
mbe
r pe
r sq
uare
cen
timet
re in
mag
netic
sub
stan
ces
by th
e le
tter
B.
The
rel
atio
n of
B to
H m
ay b
e ta
ken
as th
e pe
rmea
bilit
y(A
) of
the
_B
-an
d B
= c
c H
Tak
ing
the
abov
e fi
gure
s as
an
exam
ple,
B =
16,
000
and
H =
50
The
per
mea
bilit
y of
the
iron
= 1
6,00
0 =
5032
0
'rho
degr
ee o
f pe
rmea
bilit
y of
mag
netic
sub
stan
ces
is c
ompa
red
with
the
perm
eabi
lity
ofai
r, th
e la
tter
bein
g ta
ken
as u
nity
.T
he v
alue
42N
OT
ES
ON
TE
LE
GR
APH
Y.
of th
e pe
rmea
bilit
y of
a b
ody,
how
ever
, dec
reas
es a
s th
e m
agne
tisat
ion
incr
ease
s be
yond
a c
erta
in p
oint
tow
ards
sat
urat
ion.
Tha
t is
to s
ay, w
ithan
incr
ease
of
the
mag
netis
ing
forc
e, th
e va
lue
of th
e pe
rmea
bilit
y is
not
mai
ntai
ned
beyo
nd c
erta
in li
mits
.
Iron
is, t
here
fore
, hig
hly
susc
eptib
le to
mag
netis
atio
n, a
nd, i
n co
nse-
quen
ce, s
tron
g po
les
are
prod
uced
at i
ts e
nds
whe
n th
e m
etal
is p
lace
d in
a m
agne
tic f
ield
.
The
co
-eff
icie
nt o
f m
agne
tisat
ion
or s
usce
ptib
ility
of
any
subs
tanc
ede
pend
s up
on th
e nu
mbe
r of
uni
ts o
f m
agne
tic s
tren
gth
deve
lope
d at
its p
oles
.
EL
EC
TR
O.M
AG
NE
TS.
A h
elix
into
whi
ch a
sof
t iro
n co
re is
pla
ced
form
s, w
ith th
e co
re, a
nel
ectr
o-m
agne
t ;th
e m
agne
tic s
tren
gth
of th
e co
mbi
natio
n be
ing
muc
hgr
eate
r th
an th
at o
f th
e he
lix.
The
mag
netic
eff
ect m
ay b
e fu
rthe
rin
crea
sed
by w
indi
ng a
larg
e nu
mbe
r of
turn
s of
wel
l -in
sula
ted
wir
e,la
yer
upon
laye
r, a
roun
d th
e co
re.
The
re a
re li
mits
, how
ever
, to
the
num
ber
of c
onvo
lutio
ns th
at m
ay b
e us
eful
ly e
mpl
oyed
, for
, unl
ess
the
core
lies
with
in th
e m
agne
tic f
ield
of
each
turn
of
wir
e, a
use
less
res
ist-
ance
is in
trod
uced
with
out a
ugm
entin
g th
e m
agne
tic s
tren
gth
of th
eel
ectr
o-m
agne
t.It
is f
redu
ently
sta
ted
that
ele
etro
-mag
nets
wou
nd to
a h
igh
resi
stan
cesh
ould
be
used
upo
n lo
ng li
nes,
whi
le th
ose
wou
nd to
a lo
w r
esis
tanc
esh
ould
be
empl
oyed
upo
n sh
ort l
ines
.It
is, h
owev
er, m
ore
a qu
estio
n of
the
num
ber
of tu
rns
of w
ire
in a
giv
en s
pace
than
the
actu
al r
esis
tanc
e of
the
elec
tro-
mag
net.
Whe
n a
larg
e nu
mbe
r of
con
volu
tions
is u
sed,
whi
chw
ould
be
the
case
upo
n lo
ng li
nes
of h
igh
resi
stan
ce, t
he w
ire
wou
ldne
cess
arily
be
of a
sm
all g
auge
to e
nsur
e th
at th
e m
agne
tic f
ield
due
toth
e ou
ter
laye
rs s
houl
d af
fect
the
core
.If
the
inco
min
g cu
rren
t is
wea
ka
larg
e nu
mbe
r of
con
volu
tions
is r
equi
red
to m
ultip
ly th
e m
agne
ticef
fect
; but
the
incr
ease
d re
sist
ance
doe
s no
t app
reci
ably
affe
ctth
ein
com
ing
curr
ent,
as th
e re
sist
ance
of
the
line
is c
ompa
rativ
ely
high
.W
hen
a st
rong
cur
rent
is r
ecei
ved
the
num
ber
of tu
rns
of w
ire
may
be
muc
h le
ss to
pro
duce
an
equa
l mag
netic
eff
ect-
henc
e th
e em
ploy
men
t of
elec
tro-
mag
nets
of
vary
ing
resi
stan
ces
upon
cir
cuits
of
vary
ing
leng
ths.
Whe
n it
is -
requ
ired
to w
ind
an e
lect
ro-m
agne
t to
a gi
ven
resi
stan
ce it
shou
ld b
e re
mem
bere
d th
at th
e th
icke
r th
e w
ire
the
grea
ter
will
be
the
num
ber
of c
onvo
lutio
ns; t
here
is a
lso
less
ris
k of
the
coils
bec
omin
gfu
sed
if v
ery
stro
ng c
urre
nts
are
acci
dent
ally
pas
sed
thro
ugh
them
.T
he w
ire
used
by
the
Bri
tish
Post
Off
ice
is o
f pu
re c
oppe
r, w
ell i
nsul
ated
with
silk
, and
usu
ally
wou
nd u
pon
the
core
fro
m le
ft to
rig
ht, i
.e.,
righ
t-ha
nded
ly.
Surr
ound
ing
the
soft
iron
cor
es a
re e
boni
te b
obbi
ns w
hose
diam
eter
s do
not
exc
eed
two
-fif
ths
of th
e le
ngth
of
the
core
s, a
nd th
e w
ire
NO
TE
S O
N T
EL
EG
RA
PHY
.43
is w
ound
upo
n th
e bo
bbin
s.T
he c
ores
are
cyl
indr
ical
, and
hav
e so
ft ir
onpo
le p
iece
s at
tach
ed.
A ty
pica
l ele
ctro
-mag
net o
f th
e ho
rse
-sho
e pa
ttern
is s
how
n in
Fig
. 21.
The
two
sect
ions
mus
t be
wou
nd in
the
sam
e di
rect
ion
;th
eore
tical
ly,
the
two
limbs
rep
rese
nt a
str
aigh
t ele
etro
-mag
net,
bent
into
this
sha
pe;
the
win
ding
wou
ld th
eref
ore
be c
ontin
uous
thro
ugho
ut th
e w
hole
leng
th,
and
in th
e sa
me
dire
ctio
n.In
pra
ctic
e a
soft
iron
arm
atur
e pl
aced
adj
acen
t to
the
pole
pie
ces
isac
ted
upon
indu
ctiv
ely
by th
e m
agne
tised
cor
es a
nd a
ttrac
ted
tow
ards
them
.W
hen
the
mag
netis
ing
curr
ent c
ease
s th
e ar
mat
ure
is r
esto
red
to it
sno
rmal
pos
ition
by
mea
ns o
f a
spri
ng, o
r so
me
othe
r m
echa
nica
l con
-tr
ivan
ce.
Som
etim
es, h
owev
er, r
esid
ual m
agne
tism
aff
ects
the
rapi
dw
orki
ng o
f th
e ar
mat
ure
and
prod
uces
slu
ggis
hnes
s. T
he e
ffec
ts o
f re
sidu
alm
agne
tism
are
usu
ally
app
aren
t whe
n th
e co
res
are
not w
ell a
nnea
led,
or
whe
n th
e ar
mat
ure
has
been
allo
wed
to to
uch
them
.T
his
smal
l am
ount
of r
etai
ned
or r
esid
ual m
agne
tism
is d
ue in
a g
reat
mea
sure
to th
ech
emic
al c
ompo
sitio
n an
d m
echa
nica
l con
stru
ctio
n of
the
mat
eria
l use
das
a c
ore,
its
effe
cts
bein
g ve
ry p
rono
unce
d in
bad
ly a
nnea
led
iron
aft
er th
ece
ssat
ion
of th
e m
agne
tisin
g cu
rren
t.
FIC
.2.I
.
Ele
ctrb
-mag
nets
, the
coi
ls o
f w
hich
are
trav
erse
d by
rap
idly
alte
rnat
ing
curr
ents
, i.e
., cu
rren
ts w
hich
pas
s fi
rst i
n on
e di
rect
ion
and
then
in th
eot
her
with
gre
at r
apid
ity, h
ave
core
s w
hich
are
eith
er c
ompo
sed
of a
bund
le o
f so
ft ir
on w
ires
, or
have
hol
low
cor
es w
ith a
sho
rt s
lit m
ade
leng
thw
ise
in th
em.
The
latte
r fo
rm is
mos
t gen
eral
ly u
sed.
The
obj
ect
of th
ese
spec
ial c
ores
is to
elim
inat
e w
hat i
s te
rmed
" e
ddy
curr
ents
" s
etup
in s
olid
cor
es.
In h
igh
spee
d w
orki
ng, a
nd w
hen
alte
rnat
ing
curr
ents
are
appl
ied,
thes
e ed
dy c
urre
nts
are
gene
rate
d in
sol
id c
ores
con
sequ
ent
upon
the
rapi
d m
agne
tic c
hang
es in
the
iron
.
MN
OT
SB C
3 T
EL
EG
RA
PHY
.
brim
or V
vol
iN, w
hat I
N th
e re
sulta
nt c
urre
nt th
roug
h an
ext
erna
lre
sist
-
1611
1hi i
ll IN
AIM
S6
e -
4 e
=10
rR
12-8
lb+
113
0
41
ampe
re, o
r 25
mill
iam
pere
s.=
160
=40
I f
tho
cells
wor
e eq
ually
div
ided
, and
the
two
sets
arr
ange
d in
opp
ositi
on,
no c
urre
nt w
ould
flo
w, a
s th
e op
posi
ngel
ectr
o-m
otiv
e fo
rces
wou
ld b
e
equa
l.In
oth
er w
ords
, the
re w
ould
be
no d
iffe
renc
e of
pot
entia
l bet
wee
nth
e te
rmin
als
of th
e ba
ttery
.
NO
TE
S O
N T
EL
EG
RA
PHY
.39
CH
APT
ER
V.
EL
EC
TR
O-M
AG
NE
TIS
M.
A w
ire
thro
ugh
whi
ch a
cur
rent
isfl
owin
g ex
hibi
ts m
agne
tic p
rope
rtie
sso
long
as
the
curr
ent i
s su
stai
ned.
A c
ondu
ctor
may
be
eith
er a
mag
netic
subs
tanc
e or
a n
on-m
agne
tic s
ubst
ance
with
out
affe
ctin
g ei
ther
the
dis-
trib
utio
n or
the
exte
nt o
fits
fie
ld o
f fo
rce.
The
mag
netic
fie
ld is
den
oted
by th
e lin
es o
f fo
rce
whi
ch r
adia
te in
con
cent
ric
circ
les
from
the
wir
e,th
eir
com
mon
cen
tre.
Plun
ge a
cop
per
wir
e, th
roug
h w
hich
a f
airl
y st
rong
cur
rent
isfl
owin
g,in
to ir
on f
iling
s, a
nd o
bser
ve th
at th
e fi
lings
are
attr
acte
d an
d ad
here
toit.
Als
o no
tice
that
they
bec
ome
deta
ched
imm
edia
tely
the
curr
ent
ceas
es.
iFIC
; 18
Pass
the
wir
e th
roug
h a
shee
t of
card
boar
d an
dsp
rink
le ir
on f
iling
sup
on th
e la
tter.
The
fili
ngs
will
arr
ange
them
selv
es in
cir
cula
r or
der
and
indi
cate
the
exte
nt o
f th
e m
agne
tic in
flue
nce
of th
ecu
rren
t.T
hey
will
sot t
hem
selv
es w
ith th
eir
axes
at t
ange
nts
to th
e lin
es o
f fo
rce
(Fig
. 18)
,:o
il be
com
e tin
y m
agne
ts.
The
rel
ativ
e po
sitio
ns o
f th
e po
les
of th
ese
mag
nets
dep
end
upon
the
dire
ctio
n of
the
curr
ent,
know
ing
whi
ch, t
he n
orth
-see
king
and
sou
th -
soot
ing
pole
s ca
n be
det
erm
ined
by
Am
pere
's r
ule,
whi
ch r
eads
:Su
ppos
em
an s
wim
min
g in
the
wir
e, w
ith th
e cu
rren
t, an
d th
at h
e tu
rnso
as
totit
er th
e m
agne
t, th
en th
e no
rth
-see
king
pol
e w
ill b
e in
the
dire
ctio
nof
his
left
han
d,
46N
OT
ES
ON
TE
LE
GR
APH
Y.
Tho
res
ista
nces
aro
in in
vers
e pr
opor
tion
to th
e sq
uare
s of
the
diam
eter
s,an
d if
d,
and
d re
pres
ent t
he r
espe
ctiv
e di
amet
ers
--
It,
:it
:(d
2)2
:(d
1)2
128
:It
::
(80)
2:
(90)
2
6,40
0 R
=12
8 x
8,10
012
8 x
8,10
0=
10,8
68R
=16
26,
400
64
Ans
wer
:16
2 oh
ms.
Exa
mpl
e 24
.-T
wo
iron
wir
es o
f eq
ual l
engt
hs h
ave
resp
ectiv
ely
resi
st-
ance
s of
128
and
162
ohm
s.If
the
diam
eter
of
the
firs
t wir
e is
90
mils
,w
hab
is th
e di
amet
er o
f th
e se
cond
?
R, :
R2
::
(d2)
2:
(d1)
212
8:
162
::
(d2)
2:
(90)
2
162
(d2)
2 =
128
x 8,
100
(d,)
2 -6
,400
128
x 8,
100
=16
2
d,V
6,40
0 =
80
Ans
wer
: 80
mils
.
In th
e tw
o pr
eced
ing
form
ulae
the
leng
ths
and
diam
eter
s of
con
duct
ors
are
deal
t with
sep
arat
ely
in r
elat
ion
tore
sist
ance
.T
he le
ngth
s an
ddi
amet
ers
will
now
be
cons
ider
ed to
geth
er.
From
the
two
form
ulae
L,
and
R, :
R, :
:(d
2)2
:(d
i)2
The
fol
low
ing
com
poun
d pr
opor
tion
is f
orm
ulat
ed -
R,
: R2
:L
, x (
d2)2
L2
x (d
i)2
Exa
mpl
e 25
.-If
two
mile
s of
wir
e 50
mils
in d
iam
eter
has
a r
esis
tanc
eof
48
ohm
s, w
hat i
s th
e re
sist
ance
of
six
milo
sof
sim
ilar
wir
e ha
ving
adi
amet
er o
f 60
mils
?
R, :
R, :
: L, x
(d2)
2: L
2 x
(d1)
248
: R2
::
2x
(60)
2:
6x
(50)
2
R,
x 2
x(6
0)2
=48
x 6
x (
50)2
R2
-48
x 6
x 2
,500
=10
02
x 3,
600
Ans
wer
:10
0 oh
ms.
NO
TE
S O
N T
EL
EG
RA
PHY
.47
Exa
mpl
e 26
.-If
two
mile
s of
wir
e 50
mils
in d
iam
eter
has
a r
esis
t-an
ce o
f 48
ohm
s, w
hat i
s th
e le
ngth
of
a w
ire
60 m
ils in
dia
met
er h
avin
ga
resi
stan
ce o
f 10
0 oh
ms
?R
,:
R2
:: L
, x (
d2)2
: L2
x (d
1)2
48: 1
00 :
:2
x (6
0)2
: L2
x (5
0)2
L2
x(5
0)2
x 48
= 2
x (
60)2
x 1
001,
2 -
2 x
3,60
0 x
100
62,
500
x 48
Ans
wer
:6
mile
s.
Exa
mpl
e 27
.-If
two
mile
s of
wir
e ha
ving
a d
iam
eter
of
50 m
ils h
as a
resi
stan
ce o
f 48
ohm
s, w
hat i
s th
e di
amet
er o
f si
x m
iles
of s
imila
r w
ire
whi
ch h
as a
res
ista
nce
of 1
00 o
hms
?
R,
R, :
:L
, x(d
2)2
: L, x
(d1
)248
:10
0:
:2
x(d
2)2
:6
x (5
0)2
100
x 2
x (d
2)2
= 6
x (
50)2
x 4
800
2 _
6 x
1200
,500
x2
48_
3,60
0
.d2x
= V
3,60
0 =
60
Ans
wer
: 60
mils
.
Exa
mpl
e 28
.-T
wo
wir
es o
f eq
ual r
esis
tanc
es a
re r
espe
ctiv
ely
8 m
iles
and
18 m
iles
in le
ngth
.If
the
diam
eter
of
the
firs
t is
120
mils
, wha
t is
the
diam
eter
of
the
seco
nd?
R,
:R
2:
L, x
(d2
)2:
L2
x (d
1)2
but a
s R
1 =
R2
L, x
(d2
)2L
,x
(d2)
28
x (d
2)2
= 1
8x
(120
)2
(d2)
2=
18x
14,4
00_
32,4
008
d2=
V32
,400
= 1
80.
Ans
wer
:18
0 m
ill.
Exa
mpl
e 29
.-T
wo
wir
es e
qual
in r
esis
tanc
e ha
ve d
iam
eter
s of
120
mils
and
180
mils
res
pect
ivel
y.If
the
leng
th o
f L
ie s
econ
d w
ire
is 1
8 m
iles,
wha
t is
the
leng
th o
f th
e fi
rst ?
R,
: R,
:L
1 x
(d2)
2:
L,
>(d
1)2
but R
, = R
2L
, x (
d2)2
= L
, x (
d1)2
L, x
(18
0)2
= 1
8 x
(120
)218
x 1
4,40
0L
, --
832
,400
Ans
wer
:8
mile
s.
The
wei
ght o
f a
cond
ucto
r de
pend
s up
on th
e le
ngth
, are
a of
cro
ss[m
otio
n, a
nd th
e m
ater
ial o
f w
hich
the
cond
ucto
r is
com
pose
d.It
sho
uld
48N
OT
ES
ON
TE
LE
GR
APH
Y.
be a
ssum
ed, h
owev
er, i
n m
akin
g co
mpa
riso
ns, t
hat w
ires
of
the
sam
em
ater
ial a
re b
eing
con
side
red
unle
ss it
is d
efin
itely
sta
ted
to th
e co
ntra
ry,
for,
not
onl
y do
the
wei
ghts
of
diff
eren
t met
als
vary
, but
the
resi
stan
ces
also
.W
eigh
t may
, the
refo
re, b
e ex
pres
sed
rela
tivel
y as
the
prod
uct o
fle
ngth
and
sec
tiona
l are
a.
Whe
re W
sig
nifi
es w
eigh
t, L
leng
th, a
nd A
are
a of
cro
ss s
ectio
n,W
= L
x A
(1)
A(2
)
and
L =
but
R
(3)
A L
ther
efor
e, s
ubst
itutin
g th
e va
lue
of A
sho
wn
in e
quat
ion
(2),
L2
w=
WIN
NE
I
w
The
res
ista
nce
of a
ny c
ondu
ctor
is, t
here
fore
, dir
ectly
pro
port
iona
l to
the
squa
re o
f th
e le
ngth
and
inve
rsel
y pr
opor
tiona
l to
the
tota
l wei
ght.
Hen
ce th
e fo
rmul
a-R
,: R
, ::
(L1)
2 x
W2
:(L
2)2
x W
,E
xam
ple
30.-
If th
ree
mile
s of
cop
per
wir
e w
eigh
ing
1,20
01bs
. has
are
sist
ance
of
6i o
hms,
wha
t is
the
resi
stan
ce o
f fi
ve m
iles
of w
ire
of th
esa
me
mat
eria
l wei
ghin
g 75
01bs
. ?
R,
: R,
::
(L1)
2x
W2
:(L
2)2
x W
161
: R2
::
(3)2
x 75
0:
(5)2
x 1,
200
R2
x (3
)2x
750
= 6
1 x
(5)2
x 1,
200
.. R
,x
25x
1,20
0-
28-a
975
0
Ans
wer
:28
-8
Res
ista
nce
may
als
o be
exp
ress
ed "
.i te
rms
of w
eigh
t and
sec
tiona
lar
ea.
R=
A
and,
sub
stitu
ting
the
valu
e of
L f
ound
in e
quat
ion
(3),
R =
Wer
rors
ram
AA
fa
and,
as
the
sect
iona
l are
a is
pro
port
iona
l to
the
squa
re o
f th
e di
amet
er,
=di
NO
TE
S O
N T
EL
EG
RA
PHY
.49
Exa
mpl
e 31
.-T
wo
wir
es w
eigh
300
1bs.
and
600
1bs.
res
pect
ivel
y.If
the
firs
t wir
e ha
s a
diam
eter
of
80 m
ils a
nd a
res
ista
nce
of 2
6 oh
ms,
wha
t is
the
resi
stan
ce o
f th
e se
cond
wir
e if
it h
as a
dia
met
er o
f 11
0m
ils ?
R,
:R
2 ::
W, x
(d2
)4:
W2
x (d
1)4
26: R
2 :
:30
0 x
(110
)4:
600
x (8
0)4
R2
x 30
0 x
(110
)4 =
26
x 60
0 x
(80)
426
x 6
00 x
(S0
)4R
2 -
300
x (1
1.0)
1A
nsw
er :
141
ohm
s (a
ppro
xim
atel
y).
In c
ases
whe
re th
e w
eigh
t per
uni
t len
gth
is s
tate
d,i.e
., th
e w
eigh
t per
mile
, or
the
wei
ght p
er y
ard,
inst
ead
of th
eto
tal w
eigh
t, th
e re
sist
ance
isdi
rect
ly p
ropo
rtio
nal t
o th
e to
tal
leng
th a
nd in
vers
ely
prop
ortio
nal t
oth
e w
eigh
t per
uni
t len
gth.
Exa
mpl
e 32
.-If
ten
mile
s of
wir
e, w
eigh
ing
1101
bs. p
er m
ile, h
as a
resi
stan
ce o
f 80
ohm
s, w
hat i
s th
e re
sist
ance
of
30 m
iles
of w
ire
of th
esa
me
mat
eria
l wei
ghin
g 35
01bs
. per
mile
2
R,
: R2
:: L
1 x
W2
: L2
x W
180
:R
2:
:10
x 35
0: 3
0x
110
10 x
350
x R
2 =
80
x 30
x 1
1080
x 3
0 x
110
R, -
10 x
300
mom
s75
4
Ans
wer
: 757
ohm
s.
Spec
ific
res
ista
nce
may
be
defi
ned
asth
e re
lativ
e re
sist
ance
of
one
cond
ucto
r to
that
of
anot
her,
whe
n bo
th c
ondu
ctor
s ar
eof
the
sam
edi
men
sion
s an
d te
sted
und
er s
imila
r co
nditi
ons.
The
spe
cifi
c re
sist
ance
sof
iron
and
cop
per
are
appr
oxim
atel
y as
6 is
to 1
.A
n ir
on w
ire
has
abou
tsi
x tim
es th
e re
sist
ance
of
a co
pper
wir
e if
the
two
are
of th
e sa
me
dim
ensi
ons.
Ifit
be d
esir
ed to
rep
lace
an
iron
con
duct
or b
y on
eof
copp
er o
f th
e sa
me
leng
th,
and
reta
in th
e sa
me
resi
stan
ce, t
he c
oppe
rw
ire
shou
ld h
ave
only
one
-si
xth
the
area
of c
ross
sec
tion
of th
e ir
on w
ire.
RE
SIST
AN
CE
CO
ILS.
Res
ista
nce
is m
easu
red
by m
akin
g co
mpa
riso
ns w
ithth
e oh
m-t
heun
it of
res
ista
nce-
or m
ultip
les
of it
.Fo
r th
is p
urpo
se s
ets
of r
esis
tanc
eco
ils a
re c
onst
ruct
ed b
y m
eans
of
whi
ch c
ompa
riso
ns m
aybe
rea
dily
mad
e.
An
ordi
nary
set
of
resi
stan
ce c
oils
is a
rran
ged
by f
ixin
ga
seri
es o
f br
ass
junc
tion
piec
es u
pon
a vu
lcan
itesl
ab a
nd c
onne
ctin
g th
e va
riou
s se
ctio
nsw
ith c
oils
of
wir
e ha
ving
fix
ed r
esis
tanc
es.
By
the
inse
rtio
n of
con
ical
bras
s pl
ugs
betw
een
the
junc
tion
piec
esth
e co
ils a
re c
ut o
ut o
f ci
rcui
t,w
hile
the
with
draw
al o
f th
e pl
ugs
caus
es th
e cu
rren
t to
trav
erse
the
coils
.
(Fig
. 23.
)
50N
OT
ES
ON
TE
LE
GR
APH
Y.
The
val
ue o
f a
set
of r
esis
tanc
e co
ils d
epen
dspr
inci
pally
upo
n th
eco
nsta
ncy
of th
e re
sist
ance
, the
acc
urac
y of
adj
ustm
ent o
f ea
chco
il to
its
nom
inal
val
ue, a
nd th
o fa
cilit
y of
re
-arr
ange
men
t to
cove
r a
larg
e ra
nge
ofre
sist
ance
s.
The
res
ista
nce
of m
ost b
odie
s is
aff
ecte
dby
tem
pera
ture
.L
iqui
ds, a
ndse
mi -
cond
ucto
rs g
ener
ally
, dec
reas
e in
resi
stan
ce w
ith a
ris
e in
tem
pera
-tu
re, b
ut th
e re
sist
ance
of
met
als
incr
ease
s if
thei
rte
mpe
ratu
re is
rai
sed.
Tho
res
ista
nce
of a
lloys
, how
ever
, is
prac
tical
ly u
naff
ecte
d by
a v
aria
tion
of te
mpe
ratu
re, a
nd f
or th
isre
ason
Ger
man
silv
er a
nd p
latin
oid
are
the
met
als
mos
t fre
quen
tly e
mpl
oyed
in th
eco
nstr
uctio
n of
res
ista
nce
coils
.T
he a
lloys
pos
sess
aco
mpa
rativ
ely
high
spe
cifi
c re
sist
ance
.T
he w
ire,
whi
ch is
usu
ally
cov
ered
with
two
laye
rs o
f si
lk s
atur
ated
with
sol
idpa
raff
in to
insu
re g
ood
insu
latio
n, is
doub
ly w
ound
upo
n la
rge
hollo
wbo
bbin
s.T
he o
bjec
t of
doub
le w
indi
ng is
to o
bvia
teth
e ef
fect
s of
sel
f-in
duct
ion.
Whe
n a
curr
ent
isse
ntth
roug
h a
coil
of w
ire
" ex
tra
curr
ents
" a
re s
et u
p in
the
coil
byel
ectr
o-na
gnet
ic in
duct
ion
;bu
t whe
nth
e co
il is
dou
bly
wou
nd (
Fig.
23)
the
extr
a cu
rren
t gen
erat
ed in
one
II le
r
::111
311:
.'
r.td (c
*t=
4.-)
t'
sect
ion
is n
eutr
alis
ed b
y th
e ex
tra
curr
ent s
etup
in th
e op
posi
te d
irec
tion
in th
e ot
her
sect
ion
of th
e co
il, a
nd th
e ef
fect
s of
self
-ind
uctio
n ar
e co
n-se
quen
tly e
limin
ated
.
The
coi
ls r
equi
red
for
smal
l res
ista
nces
sho
uld
bem
ade
of th
ick
wir
e.If
a s
hort
wir
e of
sm
all g
auge
wer
e us
ed th
e ex
act v
alue
requ
ired
wou
ld b
efa
r m
ore
diff
icul
t to
obta
in th
an if
a lo
nger
wir
e of
grea
ter
area
of
cros
sse
ctio
n w
ere
empl
oyed
.It
is im
port
ant t
hat t
he v
alue
of
each
coi
l sho
uld
be a
s ac
cura
te a
s po
ssib
le, f
or, a
lthou
gh a
ner
ror
in e
ach
indi
vidu
al c
oil
may
be
inap
prec
iabl
e, th
e ac
cum
ulat
ed e
rror
s of
the
set
may
be
cons
ider
-ab
le.
Whe
n te
sted
eac
h co
il sh
ould
poss
ess
a re
sist
ance
cor
resp
ondi
ngw
ith th
e m
arke
d va
lue,
and
the
resi
stan
ce o
fa
seri
es o
f co
ils s
houl
d be
equa
l. to
the
indi
vidu
al r
esis
tanc
es a
dded
toge
ther
.A
set
of
coils
by
mea
ns o
f w
hich
it is
poss
ible
to o
btai
n re
sist
ance
sva
ryin
g fr
om 1
ohm
to 1
1,11
0 oh
ms
is m
ade
up o
f 16
coi
ls, h
avin
gva
lues
of
1, 2
, 2, 5
;10
, 20,
20,
50
;10
0, 2
00, 2
00, 5
00 ;
1,00
0, 2
,000
, 2,0
00,
and
5,00
0 oh
ms
resp
ectiv
ely.
NO
TE
S O
N T
EL
EG
RA
PHY
.51
JOIN
T R
ESI
STA
NC
E.
Whe
n se
vera
l wir
es a
re jo
ined
toge
ther
in s
erie
s th
e to
tal
resi
stan
ce is
the
sum
of
the
sepa
rate
res
ista
nces
.It
is f
requ
ently
adv
anta
geou
s, h
ow-
ever
, to
join
wir
es in
" pa
ralle
l "or
" m
ultip
le a
rc."
Cir
cuits
join
ed u
pin
this
man
ner,
so
as to
pro
duce
a d
ivis
ion
of th
ecu
rren
t at a
junc
tion
oftw
o or
mor
e ,,s
ista
,nce
s, a
re u
sual
ly te
rmed
" di
vide
d "
circ
uits
, and
the
resi
stan
ces
of th
efn
rm a
"jo
int "
res
ista
nce.
In F
ig. 2
4 th
e re
sist
ance
of
the
circ
uit b
etw
een
the
poin
ts A
and
B is
the
join
t res
ista
nce
of th
e tw
o w
ires
.If
the
sepa
rate
res
ista
nces
of
the
two
F1C
path
s ar
e eq
ual,
then
the
join
t res
ista
nce
ofth
e ci
rcui
t bet
wee
n A
and
Bw
ill b
e ha
lf th
e re
sist
ance
of
one
of th
e br
anch
es.
For
exam
ple,
if th
e tw
o w
ires
join
ing
the
poin
ts A
and
Bha
ve e
ach
are
sist
ance
of
10 o
hms,
the
join
t res
ista
nce
of th
e tw
o w
ires
will
be 5
ohm
s.
If a
ny n
umbe
r of
equ
al r
esis
tanc
es b
e jo
ined
in"
mul
tiple
" th
eir
join
tre
sist
ance
will
be
the
resi
stan
ce o
f on
e of
them
div
ided
by
the
num
ber
empl
oyed
. The
join
t res
ista
nce
in th
is c
ase
is e
qual
to
Whe
re R
= th
e re
sist
ance
of
one
wir
ean
dN
= th
e nu
mbe
r of
wir
es s
o jo
ined
.
The
join
t res
ista
nce
of 1
0 w
ires
, eac
h ha
ving
50
ohm
s re
sist
ance
,is
5 oh
ms.
Whe
n it
is d
esir
ed to
fin
d th
e jo
int r
esis
tanc
e of
two
cond
ucto
rsw
hose
resi
stan
ces
are
uneq
ual,
the
prod
uct o
f th
e re
sist
ance
s sh
ould
be d
ivid
ed
by th
e re
sist
ance
s ad
ded
toge
ther
.
Exa
mpl
e 33
.-W
hat i
s th
e re
sist
ance
of
two
wir
esof
20
and
30 o
hms
resp
ectiv
ely
whe
n jo
ined
in "
mul
tiple
arc
" ?
Join
t res
ista
nce
+ B
2w
here
R, a
nd R
2 re
pres
ent t
he r
espe
ctiv
e re
sist
ance
s of
the
two
wir
es.
Join
t res
ista
nce
=20
x 3
0.2
030
-6°
°=
12
-50
Ans
wer
:12
ohm
s.
,
52N
OT
ES
ON
TE
LE
GR
APH
Y.
Exa
mpl
e 34
.-T
he jo
int r
esis
tanc
e of
two
wir
es jo
ined
in "
mul
tiple
aro
" is
12
ohm
s.If
one
of
the
wir
es h
as a
res
ista
nce
of 2
0 oh
ms,
wha
t is
the
resi
stan
ce o
f th
e ot
her?
Join
t res
ista
nce
=R
x R R R
,12
20 x
20 +
lt2
20 R
=12
(20
+ R
2)=
240
+ 1
2 R
220
R, -
12
R, =
240
8 R
221
0
R2
=30
Ans
wer
: 30
ohm
s.T
he c
ondu
ctiv
ity o
f a
wir
e is
the
reci
proc
al o
f its
res
ista
nce.
no
join
tco
nduc
tivity
of
any
num
ber
of w
ires
join
ed in
" m
ultip
le a
rc "
is th
esu
mof
thei
r se
para
te c
ondu
ctiv
ities
.T
he jo
int r
esis
tanc
e of
any
num
ber
ofw
ires
join
ed in
"m
ultip
le a
rc"
is th
e re
cipr
ocal
of
thei
rjo
int c
ondu
ctiv
ity.
If th
ree
wir
es h
ave
2 oh
ms,
4 o
hms,
and
6 o
hms
resi
stan
cere
spec
tivel
y,th
eir
cond
uctiv
ities
may
be
expr
esse
d as
The
join
t con
duct
ivity
of
thes
e th
ree
wir
es w
ill b
e1
+1
111
+=
2
46
12an
d th
eir
join
t res
ista
nce
112
= 1
.111
. ohm
.F
4IT
The
join
t res
ista
nce
of a
ny n
umbe
r of
wir
es jo
ined
in"m
ultip
le a
rc "
will
alw
ays
be le
ss th
an th
e sm
alle
st in
divi
dual
res
ista
nce.
The
law
of j
oint
res
ist-
ance
s m
ay b
e ex
pres
sed
thus
: W
hen
any
num
ber
of r
esis
tanc
esar
e jo
ined
in "
mul
tiple
arc
," th
eir
join
t res
ista
nce
will
be
the
reci
proc
al o
f th
e su
mof
the
reci
proc
als
of th
e in
divi
dual
res
ista
nces
, or
Join
t res
ista
nce
=1
11
++
-It
,11
'2R
3'"
4E
xam
ple
35.-
Wha
t is
the
join
t res
ista
nce
of th
ree
wir
es, t
hese
para
tere
sist
ance
s of
whi
ch a
re 1
, 2, a
nd 3
ohm
s re
spec
tivel
y ?
Join
t res
ista
nce
=1 1 T
4.r;
-Es
1
+7
+
11 6A
nsw
er .
ohm
.11
1 7 6 it
NO
TE
S O
N T
EL
EG
RA
PHY
.53
Exa
mpl
e 36
.-T
hree
wir
es, w
hose
res
ista
nces
are
res
pect
ivel
y 15
, 30,
and
900
ohm
s, a
re jo
ined
in "
par
alle
l arc
."W
hat i
s th
e jo
int r
esis
tanc
e?
Join
t res
ista
nce
1 i1
-rA
1530
900
1=
6 0
+ 3
0 +
190
090
0=
y l
=90
1
Ans
wer
:98
1 oh
ms.
Exa
mpl
e 37
.- -
Four
con
duct
ors,
who
se r
esis
tanc
es a
re r
espe
ctiv
ely
one-
thir
d, o
ne -
fift
h, o
ne -
seve
nth,
and
one
-ni
nth
of a
n oh
m, a
re jo
ined
in"
mul
tiple
arc
."W
hat i
s th
eir
join
t res
ista
nce
?
Join
t res
ista
nce
-1
11
1.L
,i
MO
NIS
M=
ftw
elm
i
11
3 +
57
+ 9
=24
Ans
wer
:1
ohm
.72
7
Exa
mpl
e 38
. -T
he jo
int r
esis
tanc
e of
thre
e w
ires
join
ed in
"m
ultip
lear
c "
is tw
o oh
ms.
If tw
o of
the
sepa
rate
res
ista
nces
are
five
and
sev
enoh
ms
resp
ectiv
ely,
wha
t is
the
thir
d re
sist
ance
?,
Let
x d
enot
e th
e un
know
n re
sist
ance
, the
n1
2
2 -2
15
7x 2
= 1
-5
-2
x 235
- 1
4 --
10
852
_11
x35
iix =
70
.. x
=A
nsw
er :
6111
. ohm
s.
44N
OT
ES
ON
TE
LE
GR
APH
Y.
Div
ided
ele
ctro
-mag
eets
are
use
d fo
r hi
gh s
peed
wor
king
.In
thes
eth
e co
re is
div
ided
into
two
sect
ions
, one
coi
l bei
ng f
itted
upo
n ea
ch, a
ndis
not
con
tinuo
us a
s in
Fig
. 21.
With
a s
oft i
ron
stra
p at
the
base
it w
asfo
und
that
, whe
n th
e ar
mat
ure
was
attr
acte
d at
rap
id in
terv
als,
a c
lose
dm
agne
tic c
ircu
it w
as p
ract
ical
ly f
orm
ed, a
nd s
elf-
indu
ctio
n, to
be
expl
aine
dla
ter,
bec
ame
very
gre
at.
Self
-ind
uctio
n m
ost s
erio
usly
aff
ects
the
wor
k-in
g sp
eed,
but
is c
onsi
dera
bly
redu
ced
by th
is s
light
alte
ratio
n.A
spe
cial
kin
d of
ele
ctro
-mag
net (
Fig.
22)
, inv
ente
d by
Pro
fess
or H
ughe
s,
FIG
. 22
is o
f gr
eat i
mpo
rtan
ce in
con
nect
ion
with
the
Hug
hes'
type
-pr
intin
gin
stru
men
t.A
per
man
ent s
teel
mag
net,
of th
e co
mpo
und
or la
min
ated
for
m, i
s fi
tted
with
two
soft
iron
pol
e pi
eces
, a c
oil o
f w
ire
bein
g w
ound
upo
n ea
ch.
The
pol
e pi
eces
or
core
s ar
e ac
ted
upon
indu
ctiv
ely
by th
e pe
rman
ent
mag
net,
and
thes
e in
turn
attr
act a
n ar
mat
ure
of s
oft i
ron
and
hold
it in
clos
e pr
oxim
ity to
the
coils
.T
he in
com
ing
curr
ent t
rave
rses
the
coils
in a
dir
ectio
n w
hich
tend
s to
reve
rse
the
pola
rity
of
the
core
s, th
e at
trac
tive
forc
e up
on th
e ar
mat
ure
bein
g co
nseq
uent
ly w
eake
ned.
To
illus
trat
e th
e ef
fect
, con
side
r th
e ar
mat
ure
to b
e he
ld b
y a
mag
netic
forc
e re
pres
entin
g 10
0, a
nd a
spr
ing
with
a f
orce
Of
91 a
ctin
gin
an
oppo
site
dir
ectio
n.If
the
attr
activ
e fo
rce
be w
eake
ned
by te
n as
the
effe
ct o
f th
e cu
rren
t, th
e ar
mat
ure
wou
ld b
e re
leas
ed a
nd a
ct w
ith th
e fu
llfo
rce
of th
e sp
ring
.B
y th
e m
ovem
ent o
f th
e ar
mat
ure
the
mec
hani
sm o
fth
e pr
intin
g in
stru
men
t is
set i
n m
otio
n, a
nd th
e co
ils a
re s
hort
-cir
cuite
d,an
d jo
ined
to e
arth
. A tr
ansi
ent c
urre
nt o
f su
ffic
ient
str
engt
h w
ill th
eref
ore
actu
ate
the
arm
atur
e, w
hile
a c
urre
nt o
f co
mpa
rativ
ely
long
dur
atio
n w
illha
ve n
o gr
eate
r ef
fect
upo
n it.
NO
TE
S O
N T
EL
EG
RA
PHY
.45
CH
APT
ER
VI.
RE
SIST
AN
CE
S.
The
res
ista
nce
of a
con
duct
or is
dir
ectly
pro
port
iona
l to
the
leng
th, a
ndin
vers
ely
prop
ortio
nal t
o th
e ar
ea o
f cr
oss
sect
ion
of s
uch
cond
ucto
r. T
here
sist
ance
of
two
yard
s of
wir
e is
twic
e as
gre
at a
s th
at o
f on
e ya
rd o
fsi
mila
r w
ire.
If, h
owev
er, i
t is
desi
red
to c
ompa
re th
e re
sist
ance
s of
two
wir
es o
f th
e sa
me
leng
th a
nd m
ater
ial t
he r
esis
tanc
es w
ill b
e in
vers
ely
prop
ortio
nal t
o th
e ar
eas
of c
ross
sec
tion
of th
e w
ires
.T
he a
rea
of c
ross
sect
ion
of a
cir
cula
r co
nduc
tor
is p
ropo
rtio
nal t
o th
esq
uare
of
the
diam
eter
.T
he r
esis
tanc
e of
a c
ircu
lar
cond
ucto
r is
, the
refo
re, i
nver
sely
prop
ortio
nal t
o th
e sq
uare
of
the
diam
eter
of
the
cond
ucto
r.
Exa
mpl
e 21
.-If
ten
mile
s of
cop
per
wir
e ha
s a
resi
stan
ce o
f 80
ohm
s,w
hat i
s th
e re
sist
ance
of
35 m
iles
of s
imila
r w
ire
?
The
res
ista
nces
are
in d
irec
t pro
port
ion
to th
e le
ngth
s, a
nd c
allin
gR
i and
R, t
he r
espe
ctiv
e re
sist
ance
s, a
nd L
i and
L2
the
resp
ectiv
ele
ngth
s-R
lR
, ::
Li
: L2
80:
::
10:
15
10 R
, = 1
5 x
80=
120
Ans
wer
: 120
ohm
s.
Exa
mpl
e 22
.-If
ten
mile
s of
cop
per
wir
e ha
s a
resi
stan
ce o
f 80
ohm
s,w
hat l
engt
h of
sim
ilar
wir
e W
ill h
ave
a re
sist
ance
of
120
ohm
s ?
:R
2:: L
i: L
280
:12
0:
:10
: L2
80 L
,=
1200
L2
200
15)d
0
Ans
wer
:1,
'1m
iles.
Exa
mpl
e 23
.-If
the
resi
stan
ce o
f a
wh
90 m
ils in
dia
met
er is
128
ohm
s,w
hat i
s th
e re
sist
ance
of
an e
qual
leng
th'f
sim
ilar
wir
e ha
ving
a d
iam
eter
of 8
0 m
ils ?
Not
e.-A
mil
is o
ne -
thou
sand
th p
art o
f au
inch
.
56N
OT
ES
ON
TE
LE
GR
APH
Y.
resp
ectiv
ely,
the
xnag
na w
ill te
nd to
turn
the
need
le o
ut o
f th
em
agne
ticm
erid
ian.
The
sim
ilar
pole
sof
the
mag
net a
nd th
e ne
edle
aro
mut
ually
repe
llent
,an
dth
eea
rth'
sm
agne
tism
,w
hich
tend
sto
hold
the
need
lein
the
mag
netic
mer
idia
n,w
illbe
oppo
sed
by I
that
of
the
mag
net.
With
the
mag
net a
t a c
erta
in d
ista
nce
from
the
need
le, t
he in
flue
nce
of th
e ea
rth
upon
the
latte
r w
ill b
e co
unte
rbal
ance
dby
the
oppo
sing
for
ce e
xert
ed b
y th
e fo
rmer
.A
t asl
ight
ly g
reat
erdi
stan
ce th
e fo
rce
exer
ted
betw
een
the
eart
h an
dth
e ne
edle
will
be
grea
ter
than
that
bet
wee
n th
e m
agne
t and
the
need
le, a
nd c
onse
quen
tly th
e ne
edle
will
be
cont
rolle
d by
the
prep
onde
ratin
g in
flue
nce
of th
e ea
rth.
It w
ill,
in f
act,
com
e to
res
t in
the
mag
netic
mer
idia
n, b
ut w
ill b
e he
ld in
that
posi
tion
by a
wea
ker
forc
e th
an w
ould
be
the
case
if th
e m
agne
t wer
ere
mov
ed. I
t is,
ther
efor
e, m
ore
susc
eptib
le to
the
elec
trom
agne
tic in
flue
nce
of a
cur
rent
.T
he s
ensi
tiven
ess
of th
e ne
edle
may
be
vari
ed b
y al
teri
ngth
e po
sitio
n of
the
adju
stin
gm
agne
t, an
d it
will
be
read
ily s
een
that
by
reve
rsin
g th
e po
sitio
ns o
f th
e po
les
the
mag
net w
ill a
ct w
ithth
e ea
rth
and
prod
uce
oppo
site
eff
ects
to th
ose
desc
ribe
d.
TH
E A
STA
TIC
GA
LV
AN
OM
ET
ER
.
By
usin
g w
hat i
s te
rmed
an
" as
tatic
pai
r "a
very
sen
sitiv
e in
stru
men
t may
be c
onst
ruct
ed.
An
asta
tio p
air
is a
com
bina
tion
of tw
om
agne
tic n
eedl
es
SIG
. 2.5
.of
equ
al s
tren
gth
and
size
fix
ed o
ne a
bove
the
othe
r by
mea
ns o
f a
light
non
-m
agne
tic s
ubst
ance
.T
heir
axe
s ar
e pa
ralle
l and
lie
in th
esa
me
vert
ical
plan
e.(F
ig. 2
5.)
The
ir u
nlik
e po
les,
how
ever
, are
adja
cent
, and
the
eart
h's
forc
e co
nseq
uent
ly te
nds
to tu
rn th
e ne
edle
sin
opp
osite
dir
ectio
ns.
If th
e ab
ove
cond
ition
s be
ful
fille
d, th
epa
ir w
ill b
e in
depe
nden
t of
the
eart
h's
mag
netis
m. e
It w
ill c
ome
to r
est i
nan
y po
sitio
n, a
nd th
e di
rect
ive
infl
uenc
e of
the
eart
h w
ill b
e nu
llifi
ed,
A v
ery
sens
itive
inst
rum
ent,
calle
dan
Ast
atic
Gal
vano
met
er is
con
-st
ruct
ed u
pon
this
pri
ncip
le.
The
nee
dles
are
del
icat
ely
susp
ende
d by
mea
ns o
fa
fibr
eof
uns
pun
silk
, and
the
uppe
r on
e, w
hich
ser
ves
as a
poin
ter,
rot
ates
abo
ve a
gra
duat
ed s
cale
.T
he f
ram
e of
the
inst
rum
ent
NO
TE
S di
t TE
LE
GIt
APr
itt.
57
Car
ries
the
coil,
insi
de w
hich
the
low
er n
eedl
etu
rns.
The
end
s of
the
coil
are
atta
ched
to tw
o te
rmin
als
fixe
dto
the
base
boa
rd, a
nd th
ein
stru
men
t sta
nds
upon
thre
e sc
rew
s, b
y m
eans
ofw
hich
the
coil
isbr
ough
tpa
ralle
lto
the
need
les.
The
latte
rar
ead
just
edto
the
zero
of
the
scal
e by
a s
crew
whi
ch c
arri
esth
e si
lksu
spen
ding
thre
ad. i
Thi
s ga
lvan
omet
er is
onl
y su
itabl
efo
r m
easu
ring
or
com
pari
ngfe
eble
cur
rent
s.A
s th
e ne
edle
s tu
rn th
ey b
ecom
e ob
lique
to th
e di
rect
ion
of th
e fo
rce
of th
e m
agne
tic f
ield
pro
duce
d by
the
curr
ent,
and
cons
e-qu
ently
are
not
act
ed u
pon
toth
e sa
me
adva
ntag
e as
whe
nth
e fo
rce
is
exer
ted
at r
ight
ang
les.
For
this
rea
son,
whe
n th
e de
flec
tions
are
larg
e
they
are
not
pro
port
iona
l to
the
stre
ngth
s of
the
curr
ents
pro
duci
ngth
em.
Whe
n, h
owev
er, t
he d
efle
ctio
nsdo
not
exc
eed
15 d
egre
es th
ey a
reap
prox
i-
mat
ely
prop
ortio
nal t
o th
ecu
rren
ts p
rodu
cing
them
.Fo
r in
stan
ce, a
curr
ent w
hich
pro
duce
s a
defl
ectio
nof
8 d
egre
es is
abo
ut tw
ice
as s
tron
g
as o
ne w
hich
onl
y de
flec
tsth
e ne
edle
s 4
degr
ees,
but
if a
defl
ectio
n of
32 d
egre
es is
reg
iste
red
the
curr
ent
is m
ore
than
dou
ble
the
stre
ngth
of
one
whi
ch p
rodu
ces
a de
flec
tion
of 1
6 de
gree
s.
TH
E T
AN
GE
NT
GA
LV
AN
OM
ET
ER
.
it is
not
pos
sibl
e to
con
stru
ct a
gal
vano
met
erw
hich
per
mits
of
curr
ents
bein
g m
easu
red
by d
irec
t rea
ding
sin
deg
rees
.A
n in
stru
men
t, ho
wev
er,
upon
whi
ch th
e ta
ngen
tof
the
angl
e of
def
lect
ion
is p
ropo
rtio
nal
to th
e
stre
ngth
of
the
curr
ent i
sca
lled
the
tang
ent g
alva
nom
eter
,and
is v
ery
larg
ely
used
in th
e B
ritis
hPo
st O
ffic
e.B
efor
e at
tem
ptin
g to
des
crib
eth
e co
nstr
uctio
n of
this
inst
rum
ent
itw
ill b
e w
ell t
o co
nsid
er s
ome
of
the
law
s w
hich
gov
ern
its a
ctio
n.
The
tota
l mag
netic
for
ce o
f th
eea
rth
actin
g up
on a
mag
netic
nee
dle
is
the
resu
ltant
of
two
forc
es, v
iz.,
aho
rizo
ntal
for
ce a
nd a
ver
tical
for
ce.
A m
agne
tic n
eedl
e w
hich
onl
yro
tate
s in
a v
ertic
al p
lane
will
com
eto
rest
in a
per
pend
icul
ar p
ositi
on,
with
its
nort
h -s
eeki
ng p
ole
poin
ting
dow
nwar
ds, i
f th
e pl
ane
of r
otat
ion
be e
ast a
nd w
est ;
but i
f th
e pl
ane
of
rota
tion
be n
orth
and
sou
th, t
hene
edle
(in
Lon
don)
will
mak
e an
ang
leof
abou
t 67
degr
ees
with
the
hori
zon.
Thi
s an
gle
is c
alle
d th
e an
gle
of d
ip o
r
incl
inat
ion,
and
.var
ies
in d
iffe
rent
latit
udes
.If
the
need
le b
e so
piv
oted
as to
be
capa
ble
of r
otat
ion
only
in a
hor
izon
tal p
lane
,th
en th
e ve
rtic
al
com
pone
nt o
f th
e ea
rth'
s m
agne
tism
will
not
aff
ect t
he d
efle
ctio
n, b
ut
sim
ply
tend
to d
epre
ssth
e ne
edle
mor
e fi
rmly
upo
n its
piv
ot,
whi
le th
e
hori
zont
al f
orce
will
turn
the
need
lein
to th
e m
agne
tic m
erid
ian.
The
eart
h's
mag
netic
line
s of
forc
e ar
e pr
actic
ally
uni
fcrm
ove
r an
ysm
all
spac
e, c
onse
quen
tlyth
e fo
rces
act
ing
upon
the
pole
sof
a s
mal
l mag
netic
need
le a
re e
qual
and
opp
osite
.
The
nor
th -
seek
ing
pole
of
the
need
le w
ill b
e re
pelle
d by
the
sout
h
mag
netic
pol
e of
the
eart
h, a
ndat
trac
ted
by th
e ea
rth'
s no
rth
mag
netic
158
NO
TE
S O
N T
EL
EG
RA
PIT
Y.
pole
.T
he s
outh
-se
ekin
g po
le o
f th
ene
edle
will
be
repe
lled
by th
eno
rth
mag
netic
pol
o of
the
eart
h, a
nd a
ttrac
ted
by th
e ea
rth'
s so
uth
mag
netic
polo
.T
he r
esul
tant
of
thes
e tw
ofo
rces
act
ing
upon
eac
hpo
le w
ill b
e th
e
A
FIG
2(,
FIG
2 8
F I
G7
sam
e in
str
engt
h, b
ut o
ppos
ite in
dir
ectio
n.Fu
rthe
r, o
n ac
coun
t of
the
grea
t siz
e of
the
eart
h, th
e fo
rces
actin
g up
on th
e po
les
of th
e ne
edle
are
prac
tical
ly p
aral
lel.
Whe
n tw
o eq
ual a
nd p
aral
lel f
orce
sac
t upo
n th
e en
ds o
f a
rigi
dbo
dyin
opp
osite
dir
ectio
nsso
as
to tu
rn it
upo
n its
cent
re, t
he m
axim
umtu
rnin
g ef
fect
is p
rodu
ced
whe
n th
etw
o fo
rces
act
at r
ight
angl
es to
that
bod
y.T
he tu
rnin
g ef
fect
grad
ually
dim
inis
hes
as th
e bo
dy tu
rns,
until
the
latte
r is
in th
esa
me
stra
ight
line
as
the
forc
esac
ting
upon
it,
whe
n th
e tu
rnin
g ef
fect
isze
ro a
nd th
e bo
dy c
omes
to r
est.
The
act
ual
amou
nt o
f th
e tu
rnin
g ef
fect
iseq
ual t
o th
e pr
oduc
t of
one
of th
e fo
rces
into
the
perp
endi
cula
r di
stan
ce b
etw
een
them
.In
Fig
s. 2
6, 2
7, a
nd 2
8 le
t A a
ndB
rep
rese
nt tw
o eq
ual a
ndpa
ralle
lfo
rces
act
ing
at th
e en
ds o
f th
em
agne
tic n
eedl
e N
S, th
en in
Fig
. 26
the
amou
nt o
f th
e tu
rnin
g ef
fect
will
be
A(o
r B
) m
ultip
lied
by th
e le
ngth
of
NS-
the
perp
endi
cula
r di
stan
ce b
etw
een
the
forc
es.
In F
ig. 2
7 th
e pe
rpen
dicu
lar
dist
ance
betw
een
the
forc
es is
onl
yN
C,
cons
eque
ntly
the
turn
ing
effe
ct h
as b
een
redu
ced
by th
ero
tatio
n of
the
need
le to
the
posi
tion
show
n. I
n Fi
g.28
, whe
re th
e pe
rpen
dicu
lar
dist
ance
is z
ero,
the
turn
ing
effe
ct is
nil,
and
the
need
le c
onse
quen
tly is
at r
est.
NO
TE
S O
N T
EL
EG
RA
.PT
iY.
19
The
term
a c
oupl
e is
app
lied
to a
pai
r of
for
ces
actin
gin
this
man
ner.
The
turn
ing
effe
ct is
the
mom
ent o
f tir
e co
uple
,an
d th
e pe
rpen
dicu
lar
dis-
tanc
e be
twee
n th
em is
cal
led
the
arm
of
the
coup
le.
The
for
ce e
xert
ed b
etw
een
two
mag
netic
pol
es is
dir
ectly
pro
port
iona
lto
the
prod
uct o
f th
eir
mag
netic
str
engt
hs a
nd in
vers
ely
prop
ortio
nalto
the
squa
re o
f th
e di
stan
cebe
twee
n th
em.
If, t
here
fore
, the
hor
izon
tal c
om-
pone
ntof
the
eart
h's
mag
netis
m b
ere
pres
ente
d by
H a
nd th
est
reng
th o
f ei
ther
pol
e of
a h
oriz
onta
lly -
susp
ende
dm
agne
tic n
eedl
e by
m, t
he f
orce
exe
rted
upo
nbo
th p
oles
of
the
mag
net i
s di
rect
ly p
ropo
rtio
nal
to H
x m
.T
he m
omen
t of
the
coup
le, o
r th
e tu
rnin
g ef
fect
,ho
wev
er,
will
dep
end
upon
the
posi
tion
of th
e ne
edle
, and
will
be
at a
max
imum
whe
n th
e ne
edle
is p
oint
ing
east
and
wes
t and
nil
whe
n th
e ne
edle
is in
the
mag
netic
mer
idia
n.
A f
ield
of
forc
e w
hich
act
s at
rig
ht a
ngle
s to
the
mag
netic
mer
idia
n te
nds
to m
ake
the
pole
s of
a h
oriz
onta
lly -
susp
ende
d m
agne
ticne
edle
poi
nt e
ast a
ndw
est.
Such
a c
ondi
tion
exis
ts w
hen
a w
ire
carr
ying
acu
rren
t is
plac
ed in
the
mag
netic
mer
idia
n.Fu
rthe
r, if
it c
an b
e ar
rang
ed f
or th
elin
es o
f fo
rce
deve
lope
d by
the
curr
ent t
o be
uni
form
inth
e sp
ace
thro
ugh
whi
ch th
ene
edle
turn
s, th
e fo
rces
act
ing
upon
the
pole
s of
the
need
le w
ill b
e eq
ual,
para
llel,
and
in o
ppos
ite d
irec
tions
.If
the
wir
e ca
rryi
ng th
e cu
rren
t be
wou
nd in
to a
cir
cula
r co
il, th
e di
amet
er o
f w
hich
is r
elat
ivel
yla
rge
to th
e
leng
th o
f th
e ne
edle
, the
line
s of
for
cedu
e to
the
curr
ent w
ill b
e pr
acti-
cally
str
aigh
t at a
nd n
ear
the
cent
reof
the
coil.
The
y w
ill a
lso
be e
qui-
dist
ant a
nd p
aral
lel w
ithin
the
smal
l spa
ce th
roug
hw
hich
the
need
le
turn
s.
Let
the
stre
ngth
of
the
fiel
d of
for
ce d
evel
oped
by
the
curr
ent b
e re
pre-
sent
ed b
y f.
The
for
ce e
xert
ed u
pon
both
pol
es o
f th
ene
edle
will
be
f x
m, a
nd it
will
tend
to tu
rn th
e ne
edle
out
of
the
mag
netic
mer
idia
n.T
his
forc
e w
ill o
ppos
e at
rig
ht a
ngle
s th
efo
rce
due
to th
eea
rth'
s
mag
netis
m. T
he d
irec
tive
infl
uenc
eof
the
latte
r is
to m
ake
the
mag
net
set i
tsel
f w
ith it
s po
les
poin
ting
nort
h an
d so
uth,
whi
le th
at o
f th
e fo
rmer
is to
def
lect
the
need
le f
rom
its
posi
tion
in th
e m
agne
tic m
erid
ian.
It h
asbe
en p
revi
ousl
y sh
own
that
the
mag
netic
mom
ent o
f a
coup
le o
r th
etu
rnin
g ef
fect
dep
ends
upo
n th
e po
sitio
nof
the
need
le.
Con
sequ
ently
ther
e w
ill b
e on
e po
sitio
n of
the
need
le in
whi
ch th
e m
agne
tic m
omen
t of
the
coup
le p
rodu
ced
by th
e ho
rizo
ntal
com
pone
ntof
the
eart
h's
mag
netis
mw
ill b
e co
unte
rbal
ance
d by
that
due
to th
e cu
rren
t.T
he n
eedl
e w
ill th
en
be a
t res
t.
In F
ig.
29 le
t M A
l rep
rese
nt th
e m
agne
tic m
erid
ian,
and
let t
hene
edle
N S
, piv
oted
at i
ts c
entr
e 0,
be
defl
ecte
d by
the
actio
n of
the
curr
ent t
o th
e po
sitio
n sh
own.
Com
plet
e th
e pa
ralle
logr
am N
A S
B.
S
60N
OT
ES
ON
TE
LE
GR
APH
Y.
The
mag
netic
mom
ent d
ue to
the
eart
h's m
agne
tism
is H
x m
xN A
,an
d th
at d
ue to
the
curr
ent
fx
m x
A S
.B
ut s
ince
the
need
le h
as
M m
FIG
. Z9
com
e to
res
t the
mag
netic
mom
ents
of
the
two
coup
les
are
equa
l :-
fx
lux
AS=
Ilxm
xNA
f=
II
xN
AA
8N
AT
he a
ngle
N S
A e
qual
s th
e an
gle
N 0
M, a
nd s
ince
--is
the
ratio
for
the
tang
ent o
f th
e an
gle
N S
A, f
may
be
said
to b
e pr
opor
tiona
l to
the
tang
ent o
f th
e an
gle
of d
efle
ctio
n N
0 M
.T
he s
tren
gth
of th
e fi
eld
offo
rce
fis
pro
port
iona
l to
the
stre
ngth
of
the
curr
ent w
hich
prod
uces
it,
and,
as
H is
a c
onst
ant q
uant
ity a
t any
ono
pla
ce, t
he c
urre
ntm
ay b
e sa
idto
be
prop
ortio
nal t
o th
e ta
ngen
t of
the
angl
e of
def
lect
ion.
In th
e ta
ngen
t gal
vano
met
er u
sed
by th
e Po
st O
ffic
eth
e co
il is
wou
nd,
upon
a r
ing
-sha
ped
bras
s bo
bbin
, its
dia
met
er b
eing
abo
ut 6
in.
It is
diff
eren
tially
wou
nd, e
ach
sect
ion
havi
ng a
res
ista
nce
of16
0 oh
ms.
Nea
rly
all g
alva
nom
eter
coi
ls a
re a
rran
ged
diff
eren
tially
,so
that
if e
qual
curr
ents
pas
s th
roug
h th
e tw
o se
ctio
ns in
oppo
site
dir
ectio
ns th
e ef
fect
of
one
sect
ion
upon
the
need
le n
eutr
alis
es th
e ef
fect
of
the
othe
r.If
the
curr
ents
aro
not
equ
al a
def
lect
ion
is p
rodu
ced
by v
irtu
e of
the
diff
eren
cein
thei
r st
reng
ths,
the
dire
ctio
n of
the
defl
ectio
nbe
ing
dete
rmin
ed b
y th
ecu
rren
t hav
ing
the
grea
ter
stre
ngth
.T
he n
eedl
e, w
hich
isve
ryde
licat
ely
pivo
ted
at th
e ce
ntre
ofth
e co
il,is
asm
all m
agne
t sin
.
NO
TE
S O
N T
EL
EG
RA
PHY
.61
In le
ngth
.A
ligh
tno
n-m
agne
tic p
oint
eris
fitte
dat
righ
tan
gles
toth
ece
ntre
ofth
em
agne
t,an
dro
tate
sho
rizo
ntal
lyov
era
scal
e.If
the
poin
ter
wer
e no
t use
d th
e sc
ale,
of
nece
ssity
, wou
ld b
e sm
all,
as th
e ve
ry s
hort
mag
net r
otat
es o
ver
a lim
ited
area
, and
the
scal
ew
ould
be in
conv
enie
ntly
clo
se to
the
pivo
t upo
n w
hich
the
mag
net t
urns
.G
reat
care
is n
eces
sary
in a
ttach
ing
the
poin
ter
to th
e m
agne
t. T
he p
oint
er m
ust
be p
erfe
ctly
str
aigh
t, an
d fi
xed
so a
s to
cro
ss th
e m
agne
t exa
ctly
at r
ight
angl
es.
Any
dev
iatio
n fr
om th
ese
rule
s w
ill r
esul
t in
inco
rrec
t rea
ding
sbe
ing
regi
ster
ed u
pon
the
scal
e.T
he a
djus
tmen
t may
be
veri
fied
by
send
ing
a cu
rren
t thr
ough
the
coil
of s
uffi
cien
t str
engt
h to
pro
duce
ade
flec
tion
of, s
ay, 1
00 ta
ngen
t div
isio
ns.
An
adju
stab
le r
esis
tanc
e sh
ould
be in
the
path
of
the
curr
ent,
and
shou
ld n
ow b
e ar
rang
ed s
o th
at th
eto
tal r
esis
tanc
e is
onl
y on
e-ha
lf o
f w
hat w
as in
cir
cuit
whe
n th
e re
adin
gof
100
tang
ent d
ivis
ions
was
take
n.If
a d
efle
ctio
n of
200
div
isio
ns is
not t
hen
regi
ster
ed th
e po
inte
r is
bad
ly s
et, a
nd r
equi
res
read
just
men
t to
the
mag
net.
One
-hal
f of
the
scal
e ca
rd is
div
ided
into
deg
rees
, and
upo
n th
e ot
her
port
ion
are
mar
ked
grad
uate
d di
visi
ons
whi
ch r
epre
sent
the
tang
ents
of
the
degr
ees.
The
latte
r sa
ves
refe
renc
e to
a ta
ble
of ta
ngen
ts. T
he d
efle
c-tio
n sh
ould
be
read
upo
n th
e ta
ngen
t sca
le, a
nd th
e cu
rren
t is
then
pro
-
FIG
30
port
iona
l to
the
num
ber
of ta
ngen
t div
isio
ns in
dica
ted.
Tw
o cu
rved
slo
ts,
into
whi
ch m
irro
rs a
re f
itted
, are
arr
ange
d in
the
scal
e ca
rd.
The
obj
ect
of th
e m
irro
rs is
to a
void
par
alla
x er
ror
whe
n th
e re
adin
gs a
re ta
ken.
Def
lect
ions
sho
uld
not b
e re
ad u
pon
the
scal
e fr
om a
n ob
lique
poi
nt o
f
62N
OT
ES
ON
TE
LE
GR
APH
Y
view
, but
the
obse
rver
sho
uld
plac
e hi
mse
lf in
suc
h a
posi
tion
that
the
poin
ter
obsc
ures
its
refl
ecte
d im
age
in th
e m
irro
rs.
Abo
ve th
e co
il di
cont
rolli
ng m
agne
t, ca
pabl
e of
bei
ng r
aise
d, lo
wer
ed, o
r tu
rned
upo
n its
axi
s,is
pla
ced
for
aelj
ustin
g pu
rpos
es. I
n Fi
g. 3
0 th
e co
nnec
tions
of
the
inst
rum
ent
are
show
n.Fo
ur te
rmin
als
fitte
d to
the
base
are
mar
ked
1, 2
, 3, a
nd 4
,th
e en
ds o
f th
e tw
o se
ctio
ns o
f th
e co
il be
ing
join
ed to
term
inal
s 1
and
3an
d 2
and
4 re
spec
tivel
y.W
hen
term
inal
s 2
and
3 ar
e jo
ined
as
show
nin
the
diag
ram
, the
two
sect
ions
of
the
coil
are
join
ed in
ser
ies,
and
acu
rren
t ent
erin
g th
e in
stru
men
t at 1
will
trav
erse
the
who
le le
ngth
of
the
coil
and
leav
e th
e ga
lvan
omet
er a
t 4.
A s
impl
e ke
y is
atta
ched
to th
ein
stru
men
t by
mea
ns o
f w
hich
the
sect
ion
betw
een
term
inal
s 2
and
4m
aybe
sho
rt-c
ircu
ited
at w
ill.
By
mom
enta
rily
dep
ress
ing
the
key
whe
n th
ean
gle
of d
efle
ctio
n is
incr
easi
ng in
mag
nitu
de th
e sw
ing
of th
e ne
edle
is c
heck
ed. T
he o
scill
atio
ns a
re th
us c
onsi
dera
bly
redu
ced
and
the
poin
ter
read
ily c
omes
to r
est.
The
ord
inar
y ze
ro o
f th
e ta
ngen
t sca
le is
not
gen
eral
ly u
tilis
ed. T
here
are
real
ly tw
o ta
ngen
t sca
les,
an
inne
r an
d an
out
er s
cale
.T
he f
orm
er is
divi
ded
into
100
tang
ent d
ivis
ions
on
eith
er s
ide
of th
eze
ro, a
nd th
edi
rect
ion
of th
e de
flec
tion
depe
nds
upon
the
dire
ctio
n of
the
curr
ent.
The
latte
r, w
hich
is c
alle
d th
e sk
ew s
cale
, is
alm
ost i
nvar
iabl
y us
ed.
The
zer
o
FIG
. 31.
is o
n th
e ex
trem
e le
ft o
f th
e sc
ale,
and
the
grea
t adv
anta
ge o
f a
rang
e of
200
tang
ent d
ivis
ions
is o
btai
ned.
The
piv
oted
nee
dle,
whe
n no
t und
erth
e in
flue
nce
of th
e cu
rren
t, re
mai
ns, o
f co
urse
, in
the
mag
netic
mer
idia
n,
NO
TE
S O
N T
EL
EG
RA
PHY
.63
but i
n or
der
to b
ring
the
poin
ter
to r
est a
t the
ske
w z
ero
the
coils
and
scal
e ar
e tu
rned
to th
e ri
ght t
hrou
gh a
n an
gle
of 6
0 de
gree
s.
The
gal
vano
met
er is
fitt
ed w
ith a
sys
tem
of
shun
ts, t
he v
alue
s of
whi
char
e nt
h, A
th, ;
210.
th, A
th, n
5th
, Tiu
th, a
nd A
uth
resp
ectiv
ely.
By
this
mea
ns c
urre
nts
of c
onsi
dera
ble
stre
ngth
may
be
read
ily m
easu
red
and
the
prac
tical
val
ue o
f th
e in
stru
men
t gre
atly
enh
ance
d. T
he s
hunt
s ar
e ar
rang
edbe
twee
n te
rmin
als
1 an
d 4.
To
adju
st th
e ga
lvan
omet
erit
shou
ld b
epl
aced
ata
dist
ance
of n
ot le
ss th
an 3
ft. f
rom
oth
er in
stru
men
ts, i
n th
e co
nstr
uctio
n of
whi
ch m
agne
tsor
mag
netic
subs
tanc
esar
eem
ploy
ed,
and
fixe
dso
that
the
poin
ter
com
es to
res
t at z
ero
on th
eou
ter
scal
e.T
he
cont
rolli
ngm
agne
tis
then
plac
edup
onth
est
alk
insu
cha
posi
tion
that
the
poin
ter
agai
n co
mes
to r
est a
t the
sam
e ze
ro.
A
curr
ent i
s th
en s
ent t
hrou
gh th
e co
ils o
f th
e ga
lvan
omet
er f
rom
a s
eale
dst
anda
rd d
ry c
ell.
In c
ircu
it w
ith th
e ce
ll an
d ga
lvan
omet
er is
join
ed a
resi
stan
ce c
oil o
f pl
atin
oid
wir
e w
hich
has
a r
esis
tanc
e of
abo
ut 1
,144
ohm
s.T
he c
ell i
s sp
ecia
lly s
elec
ted,
and
is o
f th
e L
ecla
nche
pat
tern
.It
has
an e
lect
ro-m
otiv
e fo
rce
of a
bout
1.5
vol
t and
a r
esis
tanc
e of
abo
ut1
ohm
.T
he a
ctua
l res
ista
nce
and
elec
tro-
mot
ive
forc
e ar
e m
arke
d up
on a
card
atta
ched
to th
e ou
tsid
e of
the
case
con
tain
ing
the
cell
and
the
plat
inoi
dco
il.T
he n
umbe
r of
tang
ent d
ivis
ions
whi
ch s
houl
d be
obt
aine
d by
usi
ngth
e pa
rtic
ular
cel
l sup
plie
d is
als
o in
dica
ted.
Thi
s de
flec
tion
is a
rriv
ed a
tby
adj
ustin
g th
e co
ntro
lling
mag
net u
pon
the
stal
k.T
he r
equi
red
sens
i-bi
lity
of th
e in
stru
men
t thu
s pr
oduc
ed b
y ad
just
ing
to o
btai
n th
e gi
ven
defl
ectio
n is
suc
h th
at a
cur
rent
of
one
mill
iam
pere
will
pro
duce
a d
efle
c-tio
n of
80
divi
sion
s.
TH
E A
BSO
LU
TE
GA
LV
AN
OM
ET
ER
.
An
inst
rum
ent b
y m
eans
ol w
hich
the
stre
ngth
of
a cu
rren
t may
be
mea
sure
d in
abs
olut
e un
its is
cal
led
an a
bsol
ute
galv
anom
eter
.T
he
tang
ent g
alva
nom
eter
may
be
so e
mpl
oyed
.T
he f
orce
by
whi
ch a
mag
netic
nee
dle
is d
efle
cted
is d
irec
tly p
ropo
rtio
nal t
o th
e le
ngth
of
the
coil
and
inve
rsel
y pr
opor
tiona
l to
the
squa
re o
f th
e di
stan
ce b
etw
een
the
need
le a
nd th
e co
il.
By
usin
g an
inst
rum
ent w
hich
has
a c
oil o
f la
rge
diam
eter
the
leng
th o
fw
ire
for
each
con
volu
tion
is g
reat
, but
it m
ust b
e re
mem
bere
d th
at th
egr
eate
r th
e di
amet
er o
f th
e co
il th
e fa
rthe
r th
e ne
edle
will
be
away
fro
mth
e w
ire.
The
eff
ect o
f in
crea
sing
the
circ
umfe
renc
e of
the
coil
is to
aug
-m
ent t
he f
orce
act
ing
upon
the
need
le b
y co
ncen
trat
ing
a gr
eate
r nu
mbe
r of
lines
of
forc
e in
to th
e sp
ace
thro
ugh
whi
ch th
e ne
edle
rot
ates
, and
, at t
hesa
me
time,
to d
ecre
ase
the
forc
e by
pla
cing
a g
reat
er d
ista
nce
betw
een
the
need
le a
t the
cen
tre
of th
e co
il an
d th
e co
il its
elf.
64N
o.rt
s O
N T
EL
EG
IIA
DM
.
The
cir
cum
fere
nce
of a
cir
cle
is 3
.141
59 ti
mes
its
diam
eter
, or,
as
it is
usua
lly w
ritte
n, 7
r d.
It m
ay a
lso
be s
tate
d as
2 w
r, w
here
r r
epre
sent
sth
e ra
dius
of
the
circ
le.
The
mag
netic
fie
ld d
evel
oped
by
the
curr
ent
may
ther
efor
e be
sai
d to
exe
rt a
for
ceup
on th
e m
agne
t at t
he c
entr
e of
the
coil
prop
ortio
nal t
o 2
or .?
-2.r
r1
r
As
27r
is a
n un
chan
geab
le q
uant
ity th
e fo
rce
with
whi
ch th
e ne
edle
isde
flec
ted
by a
ny g
iven
cur
rent
is in
vers
ely
prop
ortio
nal t
o th
e ra
dius
ofth
e co
il.Fr
om th
is it
fol
low
s th
at, i
n or
der
to o
btai
n a
give
n de
flec
tion,
any
incr
ease
in th
e ra
dius
of
the
coil
mus
t be
com
pens
ated
for
by
anin
crea
se in
the
stre
ngth
of
the
curr
ent.
The
cur
rent
pro
duci
ng a
giv
ende
flec
tion
may
ther
efor
e be
sai
dto
bepr
opor
tiona
lto
the
radi
us,
and,
if a
num
ber
of c
onvo
lutio
ns o
f w
ire,
den
oted
by
n, b
e us
ed, t
hecu
rren
t pro
duci
ng th
e de
flec
tion
will
be
inve
rsel
y pr
opor
tiona
l to
2w
n.
The
for
mul
aco
nseq
uent
ly b
ecom
es th
e co
nsta
nt o
f th
e in
stru
men
t,2
7r 1
1
and
the
curr
ent m
ay b
e re
ad in
abs
olut
e un
its o
n a
tang
ent g
alva
no-
met
er a
s C
=x
H x
tan.
S.
2 7r
n
It s
houl
d, o
f co
urse
, be
unde
rsto
od th
at c
alcu
latio
ns a
re m
ade
with
the
radi
us m
easu
red
in c
entim
etre
s, a
nd c
are
shou
ld b
e ta
ken
inre
adin
g th
eab
ove
to d
istin
guis
h be
twee
n fo
rce
and
stre
ngth
of
curr
ent.
If th
e re
sult
obta
ined
in a
bsol
ute
units
be
mul
tiplie
d by
ten,
the
valu
e of
the
curr
ent
will
be
in a
mpe
res,
or
prac
tical
uni
ts.
TH
E M
IRR
OR
GA
LV
AN
OM
ET
ER
.
The
mir
ror
galv
anom
eter
is a
n in
stru
men
t in
whi
ch a
hig
hde
gree
of
sens
ibili
ty is
atta
ined
.In
all
galv
anom
eter
s us
ed f
or m
easu
ring
fee
ble
curr
ents
it is
a s
ine
qua
non
that
the
mov
ing
part
s sh
ould
be
very
sm
all a
ndlig
ht.
In th
e ta
ngen
t gal
vano
met
er a
sm
all d
elic
atel
y pi
vote
dm
agne
t is
used
, and
in o
rder
that
min
ute
mov
emen
ts m
ay b
e ob
serv
ed a
nd s
mal
lde
flec
tions
acc
urat
ely
mea
sure
d, a
long
inde
x or
poi
nter
is a
ttach
ed to
the
need
le.
The
poi
nter
is d
isca
rded
in th
e m
irro
r ga
lvan
omet
er, a
ndin
its
stea
d a
refl
ecte
d be
am o
f lig
ht is
em
ploy
ed. T
he la
tter
has
the
adva
ntag
e of
bein
g w
ithou
t wei
ght a
nd in
ertia
. In
the
inst
rum
ent k
now
n as
Tho
mso
n's
Ref
lect
ing
Mir
ror
Gal
vano
met
er tw
oor
thre
e pi
eces
of m
agne
tised
wat
ch s
prin
g ab
out A
tlas
of a
n in
ch in
leng
th a
re u
sed
as th
e ne
edle
.T
hey
are
atta
ched
, with
thei
r si
mila
r po
les
poin
ting
in th
e sa
me
dire
ctio
n,to
the
back
of
a sm
all c
ircu
lar
conc
ave
mir
ror,
whi
ch is
susp
ende
d by
mea
ns o
f a
sing
le f
ibre
of
unsp
un s
ilk.
The
mir
ror
is v
ery
light
, and
its
diam
eter
is a
bout
the
leng
th o
f th
e m
agne
ts.
The
coi
l, w
hich
is c
ircu
lar,
is w
ound
upo
n a
cylin
der,
and
at i
ts c
entr
e th
e m
irro
r tu
rns.
Abo
ve th
eco
il an
adj
usta
ble
mag
net i
s pl
aced
upo
n a
stal
k, a
nd b
y th
ism
eans
the
eart
h's
infl
uenc
e is
cou
nter
acte
d.W
hen
the
mag
net i
s pl
aced
at o
rne
ar
NO
TE
S O
N T
EL
EG
RA
PHY
.65
the
low
er e
nd o
f th
e st
alk
its in
flue
nce
is s
uch
that
it c
ontr
ols
the
susp
ende
dne
edle
, and
by
turn
ing
the
mag
net
upon
its
axis
the
refl
ecte
d be
am o
f lig
htm
ay b
e re
adily
pro
ject
ed o
n to
the
zero
of
a sc
ale.
The
inst
rum
ent s
tand
sup
on th
ree
feet
, whi
ch c
arry
adj
usta
ble
scre
ws
for
leve
lling
pur
pose
s. T
hesc
ale
is p
lace
d at
a d
ista
nce
of a
bout
3ft.
from
the
galv
anom
eter
, and
fro
man
ord
inar
y la
mp,
plac
ed o
n th
e si
deof
the
scal
e re
mot
e fr
om th
ega
lvan
omet
er, a
ray
of
light
is p
roje
cted
thro
ugh
an a
pert
ure
slig
htly
belo
w th
e ce
ntre
or
zero
of
the
scal
e on
to th
e su
spen
ded
mir
ror.
(Fig
. 32.
)T
he b
eam
of
light
is r
efle
cted
to th
e sc
ale
and
prod
uces
an il
lum
inat
ed s
pot,
whi
ch, w
hen
no c
urre
nt is
pas
sing
thro
ugh
the
coil,
sho
uld
beon
the
zero
poi
nt.
Whe
n gr
eat
accu
racy
isde
sire
da
fine
wir
e is
str
etch
edpe
rpen
dicu
larl
y ac
ross
the
open
ing
thro
ugh
whi
ch th
e lig
htpa
sses
, and
read
ings
are
take
nby
the
posi
tion
ofits
sha
dow
on
the
scal
e.A
sth
ene
edle
isre
lativ
ely
smal
lto
the
size
ofth
eco
il,th
eta
ngen
tsof
the
defl
ectio
nsar
eap
prox
imat
ely
prop
ortio
nal
toth
est
reng
th o
f th
e cu
rren
ts p
rodu
cing
them
.C
onse
quen
tly th
e di
visi
ons
mar
ked
on th
e st
raig
ht s
cale
boa
rd a
re e
qual
.T
he c
oil i
s co
mpo
sed
ofm
any
turn
s of
fin
e w
ire,
and
its
resi
stan
ceis
usu
ally
abo
ut 2
,000
ohm
s.T
his
galv
anom
eter
is la
rgel
y us
ed a
s a
read
ing
inst
rum
ent
upon
long
sub
-m
arin
e ca
ble
circ
uits
, com
bina
tions
of
defl
ectio
ns to
the
righ
t and
left
pro
-du
cing
the
char
acte
rs o
f th
e M
orse
alp
habe
t.
TH
E D
'AR
SON
VA
L G
AL
VA
NO
ME
TE
R.
The
D'A
rson
val g
alva
nom
eter
is a
noth
er d
istin
ct ty
pe o
fve
ry s
ensi
tive
inst
rum
ents
.In
mos
t gal
vano
met
ers
the
curr
ent p
assi
ngth
roug
h a
coil
of w
ire
defl
ects
a s
uspe
nded
or
pivo
ted
mag
netic
nee
dle.
In
the
D'A
rson
val
galv
anom
eter
, how
ever
, thi
s co
nditi
on is
rev
erse
d, th
e co
il its
elf
bein
g
66N
OT
ES
ON
TE
LE
GR
APH
Y.
turn
ed u
pon
its p
oint
of
susp
ensi
on.
Bet
wee
n th
e po
les
of a
pow
erfu
lla
min
ated
hor
se -
shoe
mag
net t
he c
oil o
f w
ire
issu
spen
ded
by m
eans
of
aph
osph
or -
bron
ze s
trip
, thr
ough
whi
ch th
e cu
rren
t pas
ses
to th
e co
il.T
hefi
eld
of f
oroo
dev
elop
ed b
y th
e cu
rren
top
pose
s th
e m
agne
tic f
ield
of
the
mag
net i
n th
e in
torp
olar
spa
ce, a
nd a
s a
cons
eque
nce
the
coil
turn
s.A
ttach
ed to
the
coil
isan
inde
x, w
hich
mov
es h
oriz
onta
llyov
era
grad
uate
dsc
ale.
Inso
me
form
sof
the
inst
rum
ent
the
inde
xis
not
used
,bu
ta
smal
lm
irro
ran
dre
flec
ted
beam
oflig
htar
oem
ploy
edin
conj
unct
ion
with
asc
ale,
asin
the
mir
ror
galv
anom
eter
alr
eady
des
crib
ed. T
he c
hief
feat
ure
of th
e D
'Ars
onva
lga
lvan
omet
eris
itsgr
eat
sens
itive
ness
.It
sfi
gure
of
mer
it,or
the
stre
ngth
of
curr
ent w
hich
will
prod
uce
a de
flec
tion
of o
ne d
ivis
ion,
is.0
0008
mill
iam
pere
, and
the
inst
rum
ent i
sco
nseq
uent
ly u
sed
for
test
ing
in c
onne
ctio
n w
ith h
igh
resi
stan
ces,
suc
has
the
insu
latio
n re
sist
ance
of
cabl
es a
nd a
ccum
ulat
or le
ads.
Am
ong
the
othe
r ad
vant
ages
ofth
ein
stru
men
t it m
ay b
e m
entio
ned
that
the
poin
ter
com
es to
res
t with
com
-pa
rativ
ely
few
osci
llatio
ns w
hen
unde
r th
ein
flue
nce
of a
cur
rent
,an
dth
ega
lvan
omet
eris
,th
eref
ore,
said
tobe
ade
adbe
atin
stru
men
t.In
this
conn
ectio
n,ho
wev
er,
itsh
ould
best
ated
that
the
swin
gof
the
coil
issl
ow,
and
a fe
wse
cond
s m
ust b
eal
low
ed to
ela
pse
befo
re a
n ob
serv
atio
n is
mad
e.T
he p
ower
ful m
agne
tal
so p
lays
an
impo
rtan
t par
t, fo
r w
hile
rend
erin
g a
serv
ice
in m
akin
g th
ein
stru
men
t fre
e fr
om in
terf
eren
ce b
yne
ighb
ouri
ng m
agne
tic a
ppar
atus
, it
mat
eria
lly a
ffec
ts th
e re
adin
gs o
f ot
her
unpr
otec
ted
galv
anom
eter
s pl
aced
in it
s vi
cini
ty.
The
mag
net,
bein
g co
mpa
rativ
ely
heav
y, a
lso
has
the
dis-
adva
ntag
e of
mak
ing
the
galv
anom
eter
unp
orta
ble.
A s
yste
m o
f sh
unts
,to
whi
ch th
e te
rm "
Uni
vers
al "
has
bee
nap
plie
d, is
gen
eral
ly a
ttach
ed to
the
inst
rum
ent.
Thi
s pa
rtic
ular
sys
tem
of
shun
ts is
des
crib
edat
the
end
of th
is c
hapt
er.
BA
LL
IST
IC G
AL
VA
NO
ME
TE
RS.
For
the
purp
ose
of m
easu
ring
tran
sien
tcu
rren
ts, o
r cu
rren
ts w
hich
are
of s
hort
dur
atio
n, a
n in
stru
men
t is
used
in w
hich
the
mag
net m
oves
slug
gish
ly.
Thi
s co
nditi
on is
bro
ught
abo
utby
the
empl
oym
ent o
f a
mag
netic
nee
dle
whi
ch is
rel
ativ
ely
long
and
hea
vy.
The
nee
dle
is s
ome-
times
wei
ghte
d w
ith le
ad to
pro
duce
the
nece
ssar
y sl
ow m
ovem
ent,
henc
eth
e te
rm b
allis
tic o
r ba
llast
edga
lvan
omet
er.
A d
isch
arge
fro
m a
con
-de
nser
may
thus
be
mea
sure
d, a
nd th
e si
ne o
f ha
lf th
ean
gle
of th
e fi
rst
swin
g is
pro
port
iona
l to
the
quan
tity
of e
lect
rici
ty w
hich
has
pass
edth
roug
h th
e co
il.C
urre
nts
of b
rief
dur
atio
n w
hich
fol
low
eac
hot
her
inra
pid
succ
essi
on g
ive
sust
aine
d im
puls
es to
the
mov
ing
need
leun
til a
fin
alst
eady
def
lect
ion
is a
ttain
ed.
GA
LV
AN
OM
ET
ER
SH
UN
TS.
Whe
n it
is d
esir
ed to
mea
sure
a c
urre
nt o
f co
nsid
erab
lest
reng
th, i
tfr
eque
ntly
hap
pens
that
the
rang
e of
def
lect
ion
of th
ega
lvan
omet
er
NO
TE
S O
N T
EL
EG
RA
PHY
.67
empl
oyed
isno
tsu
ffic
ient
ly la
rge
to a
llow
the
mea
sure
men
t to
bem
ade
by a
dir
ect r
eadi
ng.
Whe
n th
is is
the
case
a d
efin
itefr
actio
nof
the
curr
ent i
s al
low
ed to
pas
s th
roug
h th
e co
il of
the
galv
ano-
met
er, a
nd f
rom
the
defl
ectio
n ob
serv
ed th
e st
reng
thof
the
who
lecu
rren
t is
calc
ulat
ed.
The
rem
aind
er o
f th
e cu
rren
t tra
vers
es a
noth
erpa
th, c
alle
d a
shun
t, th
e re
sist
ance
of
whi
ch b
ears
a d
efin
ite r
atio
to th
ere
sist
ance
of
the
galv
anom
eter
coi
l.Su
ppos
e th
at a
gal
vano
met
er h
avin
ga
resi
stan
ce o
f 90
ohm
s is
em
ploy
ed, a
nd th
at it
s ra
nge
of d
efle
ctio
nis
not
suf
fici
ently
larg
e to
adm
it of
a c
urre
nt o
fa
cert
ain
stre
ngth
bein
g m
easu
red.
By
join
ing
are
sist
ance
of 9
0 oh
ms
inpa
ralle
lw
ith th
e ga
lvan
omet
erco
ilth
ecu
rren
t will
split
equa
lly th
roug
hth
e tw
o pa
ths,
and
the
defl
ectio
n re
gist
ered
upo
n th
e ga
lvan
omet
er w
ill b
ea
mea
sure
of
one-
half
of
the
tota
l cur
rent
flo
win
g in
the
circ
uit.
The
mul
tiply
ing
pow
er o
f th
e sh
unt i
s sa
id to
be
2, a
nd th
e st
reng
th o
f th
ecu
rren
t whi
ch p
asse
s th
roug
h th
e ga
lvan
omet
er w
hen
a sh
unt o
f th
isva
lue
is in
ope
ratio
n sh
ould
be
mul
tiplie
d by
that
fig
ure
in o
rder
toas
cert
ain
the
tota
l cur
rent
.If
the
galv
anom
eter
be
shun
ted
by a
res
ist-
ance
of
10 o
hms,
then
by
the
law
of
divi
sion
of
curr
ent 9
-10t
hs o
f th
e w
hole
curr
ent w
ould
pas
s th
roug
h th
e sh
unt a
nd 1
-10
th th
roug
h th
e ga
lvan
o-m
eter
.T
he m
ultip
lyin
g po
wer
of
the
shun
t in
this
inst
ance
wou
ld,
ther
efor
e, b
e 10
.Fr
om th
ese
two
exam
ples
it w
ill b
e no
ticed
that
the
rela
tions
hip
exis
ting
betw
een
the
resi
stan
ce o
f th
e sh
unt a
nd th
at o
f th
ega
lvan
omet
er p
lays
an
impo
rtan
t par
t in
dete
rmin
ing
the
valu
e of
the
shun
t.A
n ex
amin
atio
n of
the
figu
res
give
n in
the
prec
edin
g ex
ampl
essh
ows
that
ifth
e re
sist
ance
of
the
galv
anom
eter
be
divi
ded
by th
ere
sist
ance
of
the
shun
t and
uni
ty a
dded
to th
e re
sult,
the
mul
tiply
ing
pow
erof
the
shun
t will
be
obta
ined
.T
his
rule
hol
ds g
ood
in e
very
cas
e, a
nd f
rom
it si
mpl
e fo
rmul
ae m
ay b
e de
duce
d w
hich
ena
ble
the
resi
stan
ce o
f th
ega
lvan
omet
er, t
he r
esis
tanc
e of
the
shun
t, or
the
mul
tiply
ing
pow
er o
f th
esh
unt t
o be
rea
dily
asc
erta
ined
, whe
n an
y tw
o of
the
thre
e qu
antit
ies
are
give
n :-
Let
G =
the
resi
stan
ce o
f th
e ga
lvan
omet
er.
S =
shun
t.m
= th
e m
ultip
lyin
g po
wer
of
the
shun
t.
The
n, s
ince
m=
+ 1
m-1
=G
= S
(m
-1)
and
S=
m-1
The
for
mul
a m
=+
1m
ay a
lso
be w
ritte
n as
mG
S
SD
2
68N
OT
ES
ON
TE
LE
GR
APH
Y.
Exa
mpl
e 10
. --A
shu
nt o
f 40
0 oh
ms
resi
stan
ce is
atta
ched
to a
gal
vano
-m
eter
whi
ch h
as a
res
ista
nce
of 2
,000
ohm
s.B
y w
hat f
igur
e m
ust t
hede
flec
tion
be m
ultip
lied
in o
rder
that
the
tota
l cur
rent
flo
win
g in
the
circ
uit m
ay b
e as
cert
aine
d ?
G-r
-
_2,
000
+-
400
= 6 Ans
wer
:6.
From
this
exa
mpl
e it
will
be
seen
that
ifth
e re
sist
ance
ofth
ega
lvan
omet
er b
e fi
ve ti
mes
that
of
the
shun
t the
mul
tiply
ing
pow
er o
fth
e sh
unt m
ust b
e 6.
Such
a s
hunt
is u
sual
ly te
rmed
a o
ne -
sixt
h sh
unt.
Exa
mpl
e 41
.-W
hat i
s th
e re
sist
ance
of
a on
e -f
ifth
shu
nt u
pon
aga
lvan
omet
er h
avin
g 32
0 oh
ms
resi
stan
ce ?
Sm
-1
320
5 -1
= 8
0
Ans
wer
: 80
ohm
s.
Exa
mpl
e 42
.-E
a o
ne -
tent
h sh
unt h
as a
res
ista
nce
of 4
0 oh
ms,
wha
tis
the
resi
stan
ce o
f th
e ga
lvan
omet
er ?
G =
S (
m-1
)=
40
(10-
1)=
360
Ans
wer
:36
0 oh
ms.
As
a jo
int r
esis
tanc
e is
for
med
whe
neve
r a
shun
t is
used
, the
res
ista
nce
of th
e sh
unte
d ga
lvan
omet
er is
less
than
the
actu
al r
esis
tanc
e of
the
inst
rum
ent c
oil.
In o
rder
, the
refo
re, t
o ke
ep th
e re
sist
ance
of
the
circ
uit
cons
tant
an
addi
tiona
l res
ista
nce
is in
trod
uced
into
the
path
of
the
curr
ent
equa
l to
the
diff
eren
ce b
etw
een
the
resi
stan
ce o
f th
e ga
lvan
omet
er c
oil a
ndth
e jo
int r
esis
tanc
e of
the
coil
and
the
shun
t.T
hus
the
amou
nt o
fco
mpe
nsat
ing
resi
stan
ce n
eces
sary
toke
ep th
ere
sist
ance
of
a ci
rcui
tco
nsta
nt is
x S S
The
arr
ange
men
t of
the
circ
uit i
s sh
own
diag
ram
atic
ally
in F
ig. 3
3 in
conn
ectio
n w
ith e
xam
ple
48.
NO
TE
S O
N T
EL
EG
RA
PHY
.69
Exa
mpl
e 43
.-W
hat s
houl
d be
the
com
pens
atin
g re
sist
ance
use
d w
hen
aon
e -f
ifth
shu
nt is
em
ploy
ed in
con
nect
ion
with
a ga
lvan
omet
er h
avin
g a
resi
stan
ce o
f 10
0 oh
ms?
oks
FIG
33.
SO 3
).'7
:5
Firs
t fin
d th
e re
sist
ance
of
the
shun
t.
m -
=10
05
-=
25
Res
ista
nce
of s
hunt
=25
ohm
s
The
com
pens
atin
g re
sist
ance
G -
G x
6
= 100 -
100
x 25
100
+ 2
5
= 100 -
2500
120
= 8
0
Ans
wer
: 80
ohm
s.
It w
ill b
e se
en th
at th
e re
sist
ance
of
the
shun
ted
galv
anom
eter
(20
ohm
s) a
dded
to th
e 80
ohm
s co
mpe
nsat
ing
resi
stan
ce is
equ
al to
the
resi
stan
ce o
f th
e un
shun
ted
galv
anom
eter
(10
0 oh
ms)
.
The
join
t res
ista
nce
prod
uced
by
the
galv
anom
eter
coi
l and
its
shun
tm
ay b
e re
adily
asc
erta
ined
by
divi
ding
the
resi
stan
ce o
f th
e fo
rmer
by
the
mul
tiply
ing
pow
er o
f th
e la
tter.
In o
rder
to s
ave
calc
ulat
ion
and
the
adju
stm
ent o
f th
e co
mpe
nsat
ing
resi
stan
ce, a
set
of
resi
stan
ce c
oils
is f
requ
ently
so
arra
nged
that
the
act
70N
OT
ES
ON
TE
LE
GR
APH
Y.
of in
sert
ing
a pl
ug to
bri
ng a
ny o
ne o
f th
e sh
unts
into
ope
ratio
n au
tom
ati-
cally
bri
ngs
the
corr
ect a
mou
nt o
f co
mpe
nsat
ing
resi
stan
ce in
to th
eci
rcui
t.
The
" U
nive
rsal
" S
yste
m o
f Sh
unts
.-T
his
syst
em is
so
calle
d be
caus
eit
can
be u
sed
in c
onne
ctio
n w
ith g
alva
nom
eter
s of
var
ious
res
ista
nces
.T
his
is p
ossi
ble
owin
g to
the
resi
stan
ce o
f th
ose
shun
ts n
ot b
eari
ng a
fix
edre
latio
nshi
p to
the
resi
stan
ce o
f an
y pa
rtic
ular
gal
vano
met
er c
oil.
G +
S.
The
mul
tiply
ing
pow
er, m
, of
a sh
unt i
s-r
-B
y ar
rang
ing
the
shun
t so
that
the
num
erat
or G
S is
kep
t con
stan
tan
d th
e de
nom
inat
or o
nly
vari
ed, t
hen
m w
ill b
e al
tere
d ac
cord
ing
to th
ere
sist
ance
of
the
shun
t.
FIG
34.
In F
ig.
34, t
he s
lidin
gle
ver
L m
oves
ove
r a
num
ber
ofst
uds
betw
een
whi
ch r
esis
tanc
e co
ils a
re f
ixed
.W
hen
the
leve
ris
inth
epo
sitio
n m
arke
d A
, the
n pr
actic
ally
the
who
le o
f th
e cu
rren
t pas
ses
thro
ugh
the
galv
anom
eter
.L
et it
be
assu
med
that
m in
this
inst
ance
is 1
.O
bvio
usly
whe
n th
ele
ver
is m
oved
to th
e po
sitio
n sh
own
in F
ig. 3
4 th
e 9,
000
ohm
s of
the
firs
tsh
unt c
oil i
s re
mov
ed to
the
galv
anom
eter
cir
cuit,
and
(G +
9,0
00)
+ S
G +
9,0
00 -
I-1,
000
G +
10,
000
m -
1,00
01,
000
or te
n tim
es w
hat i
t was
in th
e fi
rst i
nsta
nce,
whe
n
mG
+ 1
0,00
0=
10,0
00
NO
TE
S O
N T
EL
EG
RA
PHY
.71
Sim
ilarl
y by
pla
cing
the
leve
r up
on th
e ne
xt s
tud
the
resi
stan
ce o
f th
ega
lvan
omet
er c
ircu
it is
rai
sed
to G
-I-
9,00
0 +
900
, and
the
resi
stan
ce o
fth
e sh
unt i
s re
duce
d to
100
.T
here
fore
,
± 9
.000
± 9
00)
S=
G +
'=
9 00
0 +
900
+ 1
00G
10,0
0010
010
0
or 1
00 ti
mes
gre
ater
than
whe
n th
e le
ver
was
upo
n A
.
By
mov
ing
the
love
r to
the
next
con
tact
stu
d it
will
be
seen
that
m is
incr
ease
d to
1,0
00, w
hile
its
rem
oval
to th
e st
ud B
sim
ply
prod
uces
a s
hort
circ
uit a
nd n
o cu
rren
tpa
sses
thro
ugh
the
galv
anom
eter
.
It s
houl
d be
rem
embe
red
that
, with
the
univ
ersa
lsy
stem
of
shun
ts, t
heac
cept
ed r
ule
that
the
join
t res
ista
nce
of a
gal
vano
met
er a
nd it
s sh
unt
bear
s a
fixe
d re
latio
n to
the
redu
cing
pow
er o
f th
e sh
unt i
s no
t app
licab
le.
51N
OT
ES
ON
TE
LE
GR
APH
Y.
Whe
n w
ires
are
join
ed in
"mul
tiple
are
" an
d th
eir
resi
stan
ces
are
uneq
ual,
the
curr
ent w
ill d
ivid
e at
the
junc
tion
of th
e va
riou
s pa
ths.
Eac
h pa
th o
r se
ctio
n w
ill b
etr
aver
sed
by a
n am
ount
of
curr
ent i
ndi
rect
prop
ortio
n to
its
cond
uctiv
ity.
Exa
mpl
e 39
.-A
bat
tery
of
negl
igib
le r
esis
tanc
ean
d an
ele
ctro
-mot
ive
forc
e of
3 v
olts
is jo
ined
to 3
wir
esin
"m
ultip
le a
rc."
The
res
ista
nces
of
the
wir
es b
eing
10,
20,
and
40
ohm
s re
spec
tivel
y, w
hat c
urre
nt f
low
sth
roug
h ea
ch w
ire
?
Firs
t fin
d th
e jo
int r
esis
tanc
e of
the
wir
es.
Join
t res
ista
nce
=1
11
1
10_4
_
20I
= 5
'4 o
hms.
Nex
t fin
d th
e cu
rren
tem
anat
ing
from
the
batte
ry,
E
=3 55
,
21 - am
pere
or
525
m.a
.40
Now
, fin
d th
e jo
int c
ondu
ctiv
ity o
f th
e w
ires
.
Join
t con
duct
ivity
= 1
11
1020
404
+ 2
+1
-7
4040
The
cur
rent
may
, the
refo
re, b
e sa
id to
split
up
into
sev
en p
arts
, fou
r of
whi
ch p
ass
thro
ugh
the
path
of
10 o
hms
resi
stan
ce, t
wo
part
s th
roug
h th
e20
ohm
s re
sist
ance
, and
the
rem
aini
ng p
art t
hrou
gh th
e pa
th h
avin
g40
ohm
s re
sist
ance
.4 - of
525
m.a
. = 3
00 m
.a. w
ill f
low
thro
ugh
the
wir
e of
10
ohm
s.7 7
= 1
5020
1 7=
75fl
40
NO
TE
S O
N T
EL
EG
RA
PHY
.55
CH
APT
ER
VII
.G
AL
VA
NO
ME
TE
RS.
A g
alva
nom
eter
is a
n in
stru
men
t use
d to
det
ect t
he p
rese
nce
of a
curr
ent o
f el
ectr
icity
and
to m
easu
re it
s st
reng
th.
The
nam
e cl
earl
ysi
gnif
ies
its tr
ue m
eani
ng -
-a m
easu
rer
of g
alva
nism
.A
n in
stru
men
tw
hich
mer
ely
indi
cate
s ,h
e pr
esen
ce o
f a
curr
ent i
s te
rmed
a g
alva
nosc
ope.
The
fun
dam
enta
l pr
inci
ple
of th
e ga
lvan
omet
er is
bas
ed u
pon
the
fact
that
a w
ire
carr
ying
r c
urre
nt is
sur
roun
ded
by a
mag
netic
fie
ld o
f fo
rce,
whi
ch is
cap
able
of
0 if
iect
ing
a su
spen
ded
or p
ivot
ed m
agne
tic n
oodl
e fr
omits
pos
ition
of
rest
.A
str
aigh
t wir
e, u
nles
s tr
aver
sed
by a
ver
y st
rong
curr
ent,
how
ever
, pro
duce
s a
com
para
tivel
y w
eak
mag
netic
fie
ld,
and,
inor
der
to p
rovi
de ,O
r th
e m
easu
rem
ent o
f fe
eble
cur
rent
s, m
etho
ds h
ave
been
dev
ised
far
mak
ing
a m
agne
tic n
eedl
e su
scep
tible
to th
eir
infl
uenc
e.
A m
agne
tic f
ield
of
cons
ider
able
inte
nsity
may
be
prod
uced
by
win
ding
the
wir
e ca
rryi
ng th
e cu
rren
t int
o a
coil,
ther
eby
conc
entr
atin
g th
e lin
esof
for
ce in
to a
sm
all s
pace
.G
alva
nom
eter
s ar
e co
nstr
ucte
d up
on th
ispr
inci
ple.
The
num
ber
of c
onvo
lutio
ns o
f w
ire,
how
ever
, whi
ch m
ay b
eus
eful
ly e
mpl
oyed
, dep
ends
to a
cer
tain
ext
ent u
pon
the
resi
stan
ce o
f th
eci
rcui
t thr
ough
whi
ch th
e cu
rren
t is
flow
ing.
If th
e nu
mbe
r of
turn
sus
ed b
e ve
ry g
reat
the
resi
stan
ce o
f th
e co
il w
ill b
e co
nsid
erab
le.
If,
ther
efor
e,an
inst
rum
ent h
avin
g m
any
turn
sof
wir
e be
use
dto
mea
sure
acu
rren
tfl
owin
gin
aci
rcui
tof
smal
lre
sist
ance
,it
will
pro
duce
a m
arke
d di
min
utio
n in
the
stre
ngth
ofth
e cu
rren
t.T
his,
of
cour
se, i
s un
desi
rabl
e, a
s th
e ob
ject
of
the
inst
rum
ent i
sto
mea
sure
the
actu
al s
tren
gth
of th
e cu
rren
t flo
win
g in
the
circ
uit.
On
the
othe
r ha
nd, w
ith a
fee
ble
curr
ent f
low
ing
thro
ugh
a ci
rcui
t of
very
hig
hre
sist
ance
the
intr
oduc
tion
of a
gal
vano
met
er h
avin
g m
any
turn
s of
wir
ew
ill n
ot m
ater
ially
aff
ect t
he s
tren
gth
of th
e cu
rren
t, bu
t the
larg
e nu
mbe
rof
con
volu
tions
will
incr
ease
the
inte
nsity
of
the
mag
netic
fie
ld in
nea
rly
dire
ct p
ropo
rtio
n to
the
leng
th o
f w
ire
empl
oyed
.T
here
is, h
owev
er,
alw
ays
a lim
it to
the
dim
ensi
ons
of th
e co
il in
ord
er th
at th
e ou
ter
turn
sm
ay b
e ef
fect
ive.
Gen
eral
ly s
peak
ing,
a g
alva
nom
eter
of
man
y co
nvol
u-tio
ns o
f w
ire
is s
uita
ble
for
mea
suri
ng c
urre
nts
flow
ing
thro
ugh
circ
uits
of
high
res
ista
nce,
but
upo
n ci
rcui
ts o
f lo
w r
esis
tanc
e an
inst
rum
ent h
avin
gfe
w tu
rns
of w
ire
is p
refe
rabl
e.
Ano
ther
met
hod
of in
crea
sing
the
sens
itive
ness
of
a ga
lvan
omet
er is
tore
duce
the
dire
ctiv
e fo
rce
of th
e ea
rth
by u
sing
a "
com
pens
atin
g "
or"
adju
stin
g "
mag
net.
If a
bove
a m
agne
tic n
eedl
e, c
apab
le o
f ro
tatin
g in
aho
rizo
ntal
pla
ne, a
mag
net b
e pl
aced
with
its
Nor
th a
nd S
outh
see
king
pole
s po
intin
g to
the
Nor
th a
nd S
outh
mag
netic
pol
es o
f th
e ea
. tb
74N
OT
ES
ON
TE
LE
GR
APH
Y.
Tho
two
limbs
aro
yok
ed a
t the
bas
e w
ith a
sof
t iro
n st
rap.
By
the
effe
ctof
the
curr
ent o
ne p
ole
is m
ade
nort
h -s
eeki
ng a
nd th
e ot
her
sout
h -se
ekin
g.A
sof
t iro
n ar
mat
ure,
fix
ed a
t rig
ht a
ngle
s to
a m
ovab
le b
rass
love
r, is
hel
dby
adj
usta
ble
scre
ws
in c
lose
pro
xim
ity to
the
pole
s, b
ut n
ot a
ctua
llyto
uchi
ng th
em, a
nd is
act
ed u
pon
indu
ctiv
ely
by th
e el
ectr
o-m
agne
t.A
nad
just
able
spi
ral s
prin
g ho
lds
the
arm
atur
e aw
ay f
rom
the
core
s.E
ach
time
the
arm
atur
e is
attr
acte
d by
the
pass
age
of a
cur
rent
thro
ugh
the
coils
an
audi
ble
soun
d is
em
itted
, and
the
acou
stic
inst
rum
ent,
term
ed a
soun
der,
is th
us f
orm
ed. A
shu
nt, h
avin
g a
resi
stan
ce o
f 50
0 oh
ms,
isjo
ined
acr
oss
the
term
inal
s of
the
inst
rum
ent,
the
reas
on f
or w
hich
will
be
seen
late
r.
The
dir
ect s
ound
er is
in th
e lin
e ci
rcui
t, or
, in
othe
r w
ords
, is
conn
ecte
ddi
rect
ly w
ith th
e lin
e w
ire.
Thi
s ar
rang
emen
t is
in c
ontr
adis
tinct
ion
toot
her
syst
ems
in w
hich
a r
elay
is u
sed.
As
a so
unde
r re
quir
es 9
0 to
100
mill
iam
pere
s of
cur
rent
to p
rodu
ce a
wor
kabl
eef
fect
itis
onl
y us
ed"
dire
ct"
on c
ircu
its o
f sh
ort l
engt
hs w
here
the
in-c
omin
g cu
rren
ts a
refa
irly
str
ong.
It m
ay b
e m
entio
ned
here
that
the
new
est s
ound
ers
inus
e w
ith r
elay
s up
on c
ircu
its w
orke
d by
sec
onda
ry b
atte
ries
are
wou
nd to
a re
sist
ance
of
900
ohm
s.T
hey
are
shun
ted
with
coi
ls o
f 9,
000
ohm
s.
The
theo
retic
al c
onne
ctio
ns o
f a
dire
ct s
ound
er c
ircu
it ar
e sh
own
inFi
g. 3
5.T
he g
alva
nom
eter
use
d w
ith th
is s
yste
m is
not
inte
nded
as
am
easu
rer
of th
e st
reng
th o
f th
e cu
rren
t rec
eive
d or
sen
t, bu
t sim
ply
toin
dica
te th
at a
cur
rent
is f
low
ing
in th
e ci
rcui
t.It
s re
sist
ance
is30
ohm
s.
The
key
is a
sim
ply
devi
sed
bras
s le
ver
fitte
d w
ith th
ree
term
inal
s.It
sfu
nctio
n is
to c
onne
ct th
e lin
e w
ith e
ither
the
batte
ry o
r th
e re
ceiv
ing
appa
ratu
s at
will
."
UP
" A
ND
" D
OW
N "
ST
AT
ION
S.
For
the
sake
of
unif
orm
ity in
join
ing
up a
ppar
atus
a g
ener
al r
ule
isfo
llow
ed, v
iz.,
that
the
offi
ce n
eare
st L
ondo
n up
on a
ny te
legr
aph
line
isde
sign
ated
an
" up
sta
tion.
"T
he p
ositi
ve p
ole
of th
e ba
ttery
at a
n "
up "
stat
ion
is in
vari
ably
join
ed to
the
line
and
the
nega
tive
pole
to e
arth
,w
here
as a
t a "
dow
n "
stat
ion
the
reve
rse
is th
e ca
se.
At a
n in
term
edia
te s
tatio
n th
e co
nnec
tions
are
as
show
n in
Fig
. 35.
Itw
ill b
e se
en th
at th
e cu
rren
t sen
t to
the
term
inal
off
ices
is in
acc
orda
nce
with
the
abov
e ru
le.
" O
PEN
" A
ND
" C
LO
SED
" C
IRC
UIT
WO
RK
ING
.
In o
pen
circ
uit w
orki
ng, w
hich
isth
at in
gene
ral u
se in
Gre
atB
rita
in, n
o cu
rren
t pas
ses
to li
ne in
the
sing
le c
urre
nt s
yste
m u
ntil
the
key
is d
epre
ssed
.W
hen
clos
ed w
orki
ng is
res
orte
d to
, how
ever
, the
re is
norm
ally
a p
erm
anen
t cur
rent
in th
eci
rcui
t.T
his
latte
r sy
stem
NO
TE
S O
N T
EL
EG
RA
PHY
.
c43
75
72N
OT
ES
ON
TE
LE
GR
APH
Y.
CH
APT
ER
VII
I.T
EL
EG
RA
PH C
IRC
UIT
S.
A te
legr
aph
circ
uit i
s ar
rang
ed e
ither
as
a "m
etal
lic lo
op,"
or
as a
sing
le li
no w
ith a
n "
eart
h re
turn
."T
he f
orm
er s
yste
m, a
s th
e te
rmim
plie
s, n
eces
sita
tes
a se
cond
leng
th o
f w
ire,
whi
le in
the
latte
r sy
stem
an
eart
h co
nnec
tion
is m
ade
at e
ach
end
to c
ompl
ete
the
circ
uit.
The
ear
th m
ay b
e co
nsid
ered
as
a va
st r
eser
voir
of
elec
tric
ity ;
for
all
prac
tical
pur
pose
s it
isa
huge
con
duct
or, t
he r
esis
tanc
e of
whi
ch is
negl
igib
le.
The
cap
acity
of
the
eart
h is
so
imm
ense
that
its
pote
ntia
l is
norm
ally
uni
form
, and
zer
o.T
he p
oten
tial o
f al
l ele
ctri
fied
bod
ies
isco
nseq
uent
ly e
ither
abo
ve o
r be
low
that
of
the
eart
h. A
neg
ativ
e po
tent
ial
is s
aid
to b
e be
low
, a p
ositi
ve p
oten
tial a
bove
zer
o.
The
re a
re a
dvan
tage
s an
d di
sadv
anta
ges
aris
ing
from
the
use
of a
n ea
rth
retu
rn.
The
chi
ef a
dvan
tage
s ar
e th
at a
sec
ond
wir
e is
not
nec
essa
ry, a
ndth
at th
e in
itial
cos
t is
ther
efor
e co
nsid
erab
ly r
educ
ed.
The
res
ista
nce
ofa
sing
le w
ire
circ
uit i
s ab
out o
ne-h
alf
that
of
a m
etal
lic lo
op c
ircu
it, a
ndle
ss b
atte
ry p
ower
is c
onse
quen
tly n
eede
d.
The
ris
k of
fau
lts a
risi
ng is
als
o le
ss w
hen
usin
g a
sing
le w
ire
than
isth
e ca
se w
ith a
met
allic
loop
.T
he o
ne s
erio
us d
isad
vant
age,
how
ever
,up
on lo
ng li
nes
and
cabl
es m
ore
espe
cial
ly, i
s th
at a
t tim
es a
dif
fere
nce
of p
oten
tial e
xist
s be
twee
n va
riou
s po
ints
of
the
eart
h's
surf
ace.
Ear
thcu
rren
ts c
onse
quen
t upo
n th
is a
re th
en o
bser
ved
to f
low
mor
e or
less
stea
dily
alo
ng th
e w
ires
and
mat
eria
lly a
ffec
t the
wor
king
eff
icie
ncy
of
the
circ
uits
.T
hese
ear
th c
urre
nts
are
mos
t tro
uble
som
e du
ring
the
prev
alen
ce o
f su
n -s
pots
, at t
imes
whe
n au
rora
e di
spla
ys a
re e
xcep
tiona
llybr
illia
nt, a
nd d
urin
g "
mag
netic
sto
rms.
"
Ear
th c
urre
nts
may
be
elim
inat
ed f
rom
a c
ircu
it ei
ther
by
subs
titut
ing
a w
ire
for
the
eart
h as
the
retu
rn p
art
of th
e ci
rcui
t, th
us f
orm
ing
am
etal
lic lo
op, o
r by
wor
king
by
mea
ns o
f co
nden
ser
impu
lses
.In
the
form
er c
ircu
mst
ance
s th
e ea
rth
is e
ntir
ely
disp
ense
d w
ith,
and
the
diff
er-
ence
of
pote
ntia
l exi
stin
g be
twee
nth
e tw
o po
ints
of
the
eart
h's
surf
ace
is c
onse
quen
tly n
on -
effe
ctiv
e.
Whe
n a
know
ledg
e of
the
actio
n of
the
cond
ense
rha
s be
en o
btai
ned
the
stud
ent w
ill r
eadi
ly s
ee h
ow th
e ac
t of
char
ging
and
disc
harg
ing
it m
ayca
use
tran
sien
t cur
rent
s to
be
set u
pan
d em
ploy
ed a
s a
mea
ns o
f ef
fect
ive
sign
allin
g.T
he in
trod
uctio
n of
the
cond
ense
r ca
uses
abr
eak
in th
e co
ntin
uity
of
the
circ
uit,
and
eart
h cu
rren
ts b
y th
is m
eans
are
avoi
ded.
NO
TE
S O
N T
EL
EG
RA
PHY
.73
Whe
n an
ear
th r
etur
n is
use
d th
e w
ire
is f
requ
ently
sol
dere
d to
an ir
onga
s pi
pe o
r to
the
wat
er m
ain.
In b
ranc
h pi
pes
join
ts a
re n
umer
ous,
and
thes
e, to
geth
er w
ith th
e m
ater
ial u
sed
in th
eir
mak
ing,
pro
duce
unn
eces
-sa
ry r
esis
tanc
es a
nd b
ring
abo
ut w
hat i
s kn
own
as a
" b
ad e
arth
." W
hen
the
wir
es a
re w
ell s
olde
red
to a
mai
n pi
pe, h
owev
er,
a go
od e
arth
con
nec-
tion
is a
lmos
t inv
aria
bly
insu
red.
Lea
den
gas
pipe
s m
ust n
ever
be
used
,ne
ither
sho
uld
wir
es b
e la
id in
clo
se p
roxi
mity
to th
em.
Lig
htni
ng d
is-
char
ges
are
liabl
e to
fus
e le
aden
pip
es w
hils
t pas
sing
bet
wee
n th
em a
ndad
jace
nt w
ires
, and
the
risk
ofse
riou
s co
nseq
uenc
es b
y th
eir
use
isth
eref
ore
very
con
side
rabl
e.
In p
lace
s w
here
wat
er a
ndga
s m
ains
, or
othe
r su
itabl
e ea
rth
conn
ec-
tions
are
not
rea
dily
acc
essi
ble,
ear
th p
late
s ar
e em
ploy
ed.
The
y ar
eus
ually
mad
e ei
ther
of
galv
anis
ed ir
on o
r of
cop
per,
hav
ing
an a
rea
of n
ot le
ss th
an 2
i, fe
et s
quar
e.T
he p
late
s ar
e em
bedd
ed, v
ertic
ally
, in
natu
rally
moi
st s
oil,
and
the
wir
es, a
fter
hav
ing
been
pas
sed
thro
ugh
hole
sin
them
to p
reve
nt u
ndue
str
aini
ng a
t the
join
ts, a
re c
aref
ully
sol
dere
d to
the
plat
es.
Res
in s
houl
d be
use
d in
the
sold
erin
g, a
nd r
esin
, pai
nt, o
rta
r ap
plie
d to
the
join
t as
a co
atin
g to
pre
vent
moi
stur
e be
twee
n th
eso
lder
and
the
plat
es a
nd c
onse
quen
t loc
alac
tion.
The
con
nect
ing
wir
esm
ust
beof
the
sam
em
ater
ial
asth
epl
ates
,an
dof
suff
icie
ntth
ickn
ess
to a
llow
for
grad
ual d
ecay
.T
he s
ame
kind
of
met
al s
houl
d be
em
ploy
ed a
t eac
h en
d of
a li
ne to
avo
id c
urre
nts
from
an
" ea
rth
batte
ry."
With
dis
sim
ilar
met
als
as e
arth
pla
tes,
esp
ecia
lly u
pon
shor
t lin
es, t
hese
cur
rent
s m
ay c
ause
a c
onsi
dera
ble
amou
nt o
f tr
oubl
e.A
s se
vera
l wir
es a
re f
requ
ently
con
nect
ed to
the
sam
e pl
ate,
it is
impe
ra-
tive
that
all
eart
h pl
ates
sho
uld
be e
mbe
dded
in s
uita
ble
plac
es to
avo
id a
com
para
tivel
y hi
gh r
esis
tanc
e be
twee
n th
em a
nd th
e ea
rth.
A m
oist
posi
tion,
fre
e fr
om r
ocks
, is
gene
rally
sel
ecte
d, a
nd th
e re
sist
ance
off
ered
is n
ot a
llow
ed to
exc
eed
10 o
hms.
If a
com
para
tivel
y hi
gh r
esis
tanc
eex
iste
d th
e cu
rren
t fro
m o
ne w
ire,
inst
ead
of p
assi
ng to
ear
th, w
ould
divi
de, a
nd a
cer
tain
am
ount
pas
s in
to o
ther
wir
es a
ttach
ed to
the
sam
epl
ate.
A s
embl
ance
of
cont
act b
etw
een
the
circ
uits
wou
ld th
en e
nsue
.In
sto
ny a
nd c
ompa
rativ
ely
dry
plac
es it
is p
refe
rabl
e to
sin
k an
ear
th -
plat
e fo
r ea
ch w
ire
at a
dis
tanc
e of
abo
ut 5
0 ya
rds
betw
een
the
plat
es,
whi
le in
the
case
of
very
sho
rt d
ista
nces
a r
etur
n w
ire
shou
ld b
e us
ed in
the
abse
nce
of g
as o
r w
ater
mai
ns.
TH
E D
IRE
CT
SO
UN
DE
R.
The
" d
irec
t " s
ound
er c
ircu
it is
one
of
the
sim
ples
t met
hods
of
tele
-gr
aphi
csi
gnal
ling,
and
as
the
term
impl
ies,
this
sys
tem
is w
orke
d by
the
dire
ct e
ffec
t of
a cu
rren
t fro
m th
e di
stan
t sta
tion.
The
sou
nder
itse
lfis
a s
impl
e fo
rm o
f el
ectr
o-m
agne
t wou
nd to
a r
esis
tanc
e of
20
ohm
s.T
he tw
o co
ils a
re w
ound
upo
n eb
onite
bob
bins
, whi
ch la
tter
enve
lop
the
soft
iron
cor
es.
The
hor
sesh
oe p
atte
rn o
f el
eotr
o-m
agne
t is
empl
oyed
.
78N
OT
ES
ON
TE
LE
GR
APH
Y.
prod
uced
by
self
-ind
uctio
n.In
Fig
. 36
the
air
spac
e be
twee
n A
B w
ould
be e
asily
bri
dged
ove
r by
a c
urre
nt o
fve
ry h
igh
pote
ntia
l, an
d th
e co
ilits
elf
loft
unt
rave
rsod
by
the
grea
ter
port
ion
of th
e cu
rren
t.It
is u
pon
this
fac
t tha
t the
pri
ncip
le o
f lig
htni
ngpr
otec
tors
is b
ased
.
CA
RB
ON
PR
OT
EC
TO
RS.
A v
ery
effi
cien
t for
m o
f lig
htni
ng p
rote
ctor
isco
nstr
ucte
d by
sep
arat
ing
two
circ
ular
dis
cs o
f ca
rbon
by
a th
in s
heet
of
mic
ath
roug
h w
hich
thre
eho
les
aro
pier
ced.
The
line
wir
e is
con
nect
ed to
the
uppe
r di
sc, a
nd a
cont
inua
tion
of th
e w
ire,
kno
wn
as th
e "i
nstr
umen
tle
ad,"
is c
arri
ed to
4-*
To
t,70
7; I
lstr
avea
i
eVa
FIG
. 37
the
appa
ratu
s, w
hile
the
low
er d
isc
is e
arth
-con
nect
ed.
The
ligh
tnin
gle
aps
acro
ss th
e ai
r sp
ace
betw
een
the
carb
on d
iscs
and
pass
es h
arm
less
lyto
ear
th.
The
arr
ange
men
t is
show
n th
eore
tical
ly in
Fig.
37.
Car
bon
plat
es p
osse
ss a
dec
ided
adv
anta
geov
er m
etal
pla
tes,
inas
muc
has
they
are
not
fus
ed b
y th
e pa
ssag
e of
a h
eavy
cur
rent
thro
ugh
the
air
spac
e.If
bra
ss, o
r ot
her
met
al, w
ere
used
ther
ew
ould
be
a lia
bilit
y to
the
plat
es b
ecom
ing
in m
etal
lic c
onta
ct a
nd th
e lin
ew
ire
bein
g pu
t dir
ect
to e
arth
.A
noth
er a
dvan
tage
of
carb
on is
that
itis
not
ass
aila
ble
byox
ygen
as
met
als
are.
A li
ghtn
ing
prot
ecto
r in
gen
eral
use
at i
nter
med
iate
offi
ces
com
pris
es th
ree
disc
s.an
d tw
o sh
eets
of
mic
a, th
e ce
ntre
dis
c be
ing
in c
onne
ctio
n w
ith e
arth
.(F
ig. 3
8.)
The
" u
p "
and
" do
wn
"lin
esre
spec
tivel
y ar
e co
nnec
ted
to th
e tw
o ou
ter
disc
s, a
nd th
e ac
tion
of th
ispr
otec
tor
is id
entic
al w
ith th
at o
f th
e on
e al
read
y de
scri
bed.
VA
CU
UM
PR
OT
EC
TO
RS.
The
" v
acuu
m "
pro
tect
or c
onsi
sts
of a
gla
sstu
be, p
artly
exh
aust
ed o
fai
r, w
ith m
etal
con
nect
ions
at t
he e
nds.
Met
allic
pro
ject
ions
, whi
chte
rmin
ate
in p
oint
s, e
xten
d to
the
inte
rior
of
the
tube
.T
hey
are
in c
lose
prox
imity
to e
ach
othe
r, b
ut n
ot in
act
ual c
onta
ct, a
nd th
edi
scha
rge
leap
sac
ross
the
spac
e be
twee
n th
e po
ints
. One
end
of
the
tube
is in
conn
ectio
nw
ith e
arth
, whi
le th
e ot
her
end
is jo
ined
to th
e lin
ean
d in
stru
men
ts.
Thi
s ki
nd o
f pr
otec
tor
is f
requ
ently
use
d at
the
junc
tion
of u
nder
grou
ndan
d ae
rial
wir
es, a
nd is
not
aff
ecte
d by
moi
stur
e to
any
grea
t ext
ent.
A s
peci
al k
ind
of in
stru
men
t pro
tect
or k
now
nas
a "
fus
e "
is n
ow u
sed
upon
man
y ci
rcui
ts.
Bet
wee
n th
e lin
e an
d in
stru
men
tsa
glas
s tu
be
NO
TE
S O
N T
EL
EG
RA
PHY
.79
fitte
d w
ith m
etal
lic e
nds
is p
lace
d, a
nd th
e ci
rcui
t is
com
plet
ed b
y m
eans
of a
fin
e pl
atin
oid
wir
e w
hich
run
s th
roug
h th
e tu
be a
nd c
onne
cts
the
*-eT
o lip
Lig
e
Ilo
otiv
ror7
11
t-d,
a D
o,Li
edG
MM
MIII
r
FIG
.38
met
allic
end
s. A
cur
rent
of
one
ampe
re is
suf
fici
ent t
o fu
se th
e pl
atin
oid
wir
e an
d di
scon
nect
the
circ
uit.
The
inst
rum
ent c
oils
are
con
sequ
ently
save
d fr
om th
e ill
eff
ects
of
an e
xces
s cu
rren
t.
A v
ery
inge
niou
s ar
rang
emen
t has
rec
ently
bee
n in
trod
uced
as
a pr
o-te
ctio
n ag
ains
t exc
ess
curr
ents
, and
is r
ough
ly s
how
n in
Fig
. 39.
The
inco
min
g cu
rren
t,af
ter
pass
ing
thro
ugh
a pl
atin
oid
fuse
,re
ache
s
ahe
atco
ilof
abou
t10
ohm
s re
sist
ance
.A
met
allic
proj
ectio
nat
the
end
ofa
met
allic
spri
ngis
pres
sed
into
one
end
of
the
heat
coi
l, an
d is
hel
d in
pos
ition
by
mea
ns o
f so
lder
at A
. Whe
nth
e cu
rren
tpa
ssin
g th
roug
hth
ehe
atco
ilis
exce
ssiv
eth
eso
lder
F1`.
;;;. 3
9
is m
elte
d an
d th
e sp
ring
rel
ease
d.T
his
actio
n di
scon
nect
s th
e in
stru
-m
ents
, whi
ch a
re c
onne
cted
to th
e sp
ring
,fr
om th
e lin
e. A
noth
er m
etal
licsp
ring
arr
ange
d be
twee
n th
e pl
atin
oid
fuse
and
the
heat
coi
l is
held
norm
ally
aw
ay f
rom
an
eart
h -c
onne
cted
cont
act p
oint
by
mea
ns o
f an
insu
latin
g st
ud.
As
soon
as
the
firs
t spr
ing
is r
elea
sed,
the
seco
nd s
prin
gop
erat
es in
con
sequ
ence
of
the
with
draw
al o
f th
e st
ud, a
nd th
e co
nnec
tion
76N
OT
ES
ON
TE
LE
GR
APH
Y.
isla
rgel
yem
ploy
edin
Am
eric
aan
dup
on th
eC
ontin
ent.
The
adva
ntag
esof
acl
osed
circ
uit
syst
emar
enu
mer
ous
inca
ses
who
rom
any
. off
ices
are
conn
ecte
dw
ithth
esa
me
line
wir
e,an
d lit
tletr
affi
cis
deal
t with
at a
ny o
ne o
ffic
e.U
pon
shor
tlin
esth
e ba
ttery
pow
er is
em
ploy
ed a
t one
end
onl
y; b
utup
on lo
ng li
nes
it is
split
up
into
sec
tions
.In
pra
ctic
e th
e cu
rren
t fro
m th
e va
riou
s se
ctio
nsco
mbi
nes,
the
resu
lt be
ing
that
a m
uch
grea
ter
cons
tanc
y is
obt
aine
d th
anif
eac
h of
fice
sup
plie
d a
curr
ent f
rom
a s
epar
ate
sour
ce.
The
labo
urne
cess
ary
to k
eep
the
batte
ry in
ord
er is
als
o co
ncen
trat
ed a
t cer
tain
poin
ts in
stea
d of
bei
ng r
equi
red
at e
ach
offi
ce.
The
var
ious
adj
ustm
ents
nece
ssar
y fo
r di
ffer
ing
curr
ent s
tren
gths
fro
m s
ever
al b
atte
ries
are
als
oob
viat
ed. T
he s
ingl
e cu
rren
t Mor
se s
yste
m is
the
one
usua
lly a
dopt
ed, a
ndth
e ke
y is
fitt
ed w
ith a
sw
itch,
whi
ch, u
pon
bein
g tu
rned
, cut
s of
f th
epe
rman
ent
curr
ent.
An
oper
ator
at
any
stat
ion,
upo
n tu
rnin
g hi
ssw
itch,
can
sto
p th
e se
ndin
g op
erat
or a
nd r
eque
st a
rep
etiti
on.
A c
erta
in a
mou
nt o
f w
aste
is b
ound
to r
esul
t fro
m a
per
man
ent
curr
ent,
and
faul
ts w
hich
dev
elop
in c
over
ed w
ire
may
be
inte
nsif
ied
by a
con
-tin
uous
flow
ofcu
rren
t.T
he s
yste
mis
not p
opul
ar o
rge
nera
llypr
actic
able
in E
ngla
nd, a
s th
e tr
affi
c at
mos
t off
ices
fitt
ed w
ith M
orse
appa
ratu
s is
suf
fici
ent t
o m
onop
olis
e th
e us
e of
a s
epar
ate
wir
e.
NO
TE
S O
N T
EL
EG
RA
PIIY
.77
CH
APT
ER
IX
.
LIG
HT
NIN
G P
RO
TE
CT
OR
S.
Whe
n tw
o bo
dies
, suc
h as
two
clou
ds o
r th
e ea
rth
and
a cl
oud,
are
ver
yhi
ghly
cha
rged
with
ele
ctri
city
the
elec
tric
al s
tres
s ex
istin
g be
twee
n th
emis
fre
quen
tly s
uffi
cien
t to
brea
k do
wn
the
insu
latin
g m
ediu
m.
The
two
char
ges,
in th
e ac
t of
reco
mbi
ning
to p
rodu
ce e
quili
briu
m, c
ause
a di
srup
tion
of th
e in
sula
tion
and
a fl
ash,
suc
h as
that
pro
duce
d by
light
ning
, res
ults
.T
he e
ffec
t is
sim
ilar
to th
at p
rodu
ced
by th
e di
scha
rge
of a
Ley
den
jar.
The
dis
char
ge is
osc
illat
ory
in a
ctio
n, b
ut th
e os
cilla
tions
are
so r
apid
as
to c
ause
the
flas
h to
app
ear
to b
e in
one
dire
ctio
n on
ly.
Lig
htni
ng d
isch
arge
s fr
eque
ntly
take
plac
eal
ong
tele
grap
h an
dte
leph
one
wir
es, a
nd if
no
prot
ectio
n w
ere
prov
ided
con
side
rabl
e da
mag
eto
del
icat
e in
stru
men
ts w
ould
nat
ural
ly r
esul
t.T
he c
oils
of
insu
late
dw
ire
used
in th
e co
nstr
uctio
n of
ele
ctro
-mag
nets
and
gal
vano
met
ers
wou
ldbe
ren
dere
d us
eles
s if
the
insu
latio
n w
ere
dest
roye
d by
ligh
tnin
g, f
or e
ach
turn
of
wir
e w
ould
be
in d
irec
t con
tact
with
the
next
, and
the
desi
red
effe
ct o
f th
e cu
rren
t wou
ld n
ot b
e ob
tain
ed.
The
pol
arity
of
perm
anen
tm
agne
ts is
als
o lik
ely
to b
e re
vers
ed o
r de
stro
yed
by li
ghtn
ing,
and
so it
beco
mes
impe
rativ
e to
obv
iate
thes
e se
vera
l del
eter
ious
eff
ects
.
Fort
unat
ely
curr
ents
ofhi
gh p
oten
tials
, suc
has
thos
e pr
oduc
ed
by li
ghtn
ing
disc
harg
es,
have
apr
open
sity
for
leap
ing
acro
ss a
FIG
. 36.
smal
l air
spa
ce, w
hich
off
ers
an in
fini
te r
esis
tanc
e to
the
low
pot
entia
lcu
rren
ts u
sed
in te
legr
aphy
, rat
her
than
fol
low
ing
the
path
ofa
smal
l con
duct
or.
If a
coi
l of
wir
e is
in th
e pa
th o
f th
e di
scha
rge
adi
srup
tion
is p
ract
ical
ly c
erta
in, b
ecau
seof
the
chok
ing
effe
ct o
f th
e co
ils
218
IND
EX
-co
ntin
ued.
PAG
EIn
sula
tors
, fus
e17
9L
angd
on18
7In
term
edia
te s
tatio
ns74
i, te
leph
one
169
uni
vers
al w
orki
ng 1
23Jo
int c
ondu
ctiv
ity52
resi
stan
ce51
Join
ting
186
Join
ting
-box
188
Join
ting
pape
r ca
bles
190
unde
rgro
und
wir
es18
9K
.R. l
aw14
0, 1
78K
atho
de11
4K
yani
sing
181
Lan
gdon
insu
lato
r18
7L
aw, K
.R.
140,
176
Ohm
's23
Lea
ding
in w
ires
181,
187
, 215
Lec
lanc
he c
ell
14, 1
58,
aggl
omer
ate
16, 1
52L
ight
ning
dis
char
ge77
prot
ecto
rs'7
7n
carb
on78
for
cabl
es80
.re
el f
orm
of
80.
vacu
um78
Lin
es o
f fo
rce
7, 3
9, 9
0.
dist
ribu
tion
of7
Loc
al a
ctio
n14
Lod
esto
ne4
Mag
net,
adju
stin
g55
, 62,
64
,,th
e ea
rth
as a
5
Mag
netic
attr
actio
n an
d re
puls
ion
5
fiel
d, in
tens
ity o
f14
4,,
forc
es57
indu
ctio
n'7
lines
of
forc
e'7
, 39,
90
mer
idia
n5
mom
ent o
f co
uple
59su
bsta
nces
5, 1
44un
its22
Mag
netis
atio
n, c
o -e
ffic
ient
of
42M
agne
tism
'ei
4fi
rst l
aw o
f5
phys
ical
theo
ry o
f5
resi
dual
43M
agne
to b
ell
158
gene
rato
r15
9M
agne
ts, a
rtif
icia
l and
nat
ural
4co
ntro
lling
55, 6
2, 6
4te
mpo
rary
and
per
man
ent 4
, 6M
arki
ng c
urre
nt94
Meg
ohm
22M
etal
lic lo
op72
,162
com
pare
d w
ith s
ingl
e w
ire
177
Mic
rofa
rad
22M
icro
hm22
Mic
roph
one,
The
147
Mill
iam
pere
22M
illi -
volt
22M
orni
ng T
est,
The
207
Mut
ual i
nduc
tion
168
Neu
tral
rel
ay89
Num
beri
ng o
f w
ires
187
in c
able
189
Ohm
, The
22O
hm's
law
23O
hm-m
i e18
6
'1ff
neu
tral
nnn
-pol
aris
ed p
olar
ised
Rel
ayin
g so
unde
rR
esid
ual m
agne
tism
Res
ista
nce af
fect
ed b
y te
mpe
ratu
re ..
.50
coils
49co
mpe
nsat
ing
68in
sula
tion
85, 1
91in
tern
al19
join
t51
mea
sure
men
t of
.95,
201
of c
ondu
ctor
'29
of s
hnnt
67sp
ecif
ic49
, 166
,,sp
urio
us92
unit
of22
Res
ista
nces
com
pare
d45
Res
ulta
nt f
ault
167,
208
,,po
int
184
Ret
arda
tion
coils
109
Ret
entiv
ity6
Sadd
le -
brac
ket
180
Sadd
le -
stay
...18
0Sa
g18
5Se
cond
ary
cells
113
PAG
EO
pen
circ
uit w
orki
ng74
Osm
otic
act
ion
13
Ove
rhea
ring
164
Pape
r ca
bles
,,in
sula
tion
resi
stan
ce o
f 19
0,19
1190
.,jo
intin
g of
190
Para
llel a
rc, c
ells
join
ed in
29co
nduc
tors
join
ed in
51Pa
ralla
x er
ror
61Pe
rman
ent c
urre
nt s
yste
m17
0 a
dvan
tage
s of
171
Perm
eabi
lity
41Ph
osph
or b
ooze
166
Pilla
r te
st -
box
ix18
9Pi
pes,
join
ting
of18
8Pl
ante
114
Pola
rise
d re
lay
11, 1
813 86
Pola
risa
tion
Pole
-ar
ms
185
Pole
s18
5"
A "
and
" H
"18
2m
agne
tic a
nd g
eogr
aphi
cal
5pr
eser
vatio
n of
181
setti
ng o
f18
2te
rmin
al18
1Po
st O
ffic
e st
anda
rd r
elay
85Po
tent
ial
4di
ffer
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of
4, 9
zero
4, 7
2Pr
actic
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22Q
uadr
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cor
e18
9Q
uadr
uple
x12
8de
crem
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4un
iver
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183
Qua
ntity
, cel
ls jo
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in'2
9un
it of
22R
ecei
ver,
tele
phon
e15
4R
heos
tat
98R
elay
, The
85 c
oils
in"
seri
es "
and
" q
uant
ity "
86 d
iffe
rent
ially
wou
nd86 89
128,
132 86 13
043
, 94 4
IND
EX
-co
ntin
ued
PAG
ESe
cond
ary
cells
, cha
rgin
g of
118
chem
ical
act
ion
of11
7di
stri
butio
n of
vol
tage
s of
126
form
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of p
late
s of
118
elec
tro-
mot
ive
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e of
118
grou
ping
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126
resi
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ce o
fun
iver
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ries
," c
ells
join
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resi
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join
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Shun
t, ga
lvan
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mul
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er o
f...
..67
resi
stan
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f67
univ
ersa
l66
, 70
Shun
ted
cond
ense
r14
2Si
gnal
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cond
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r14
2Si
liciu
m-b
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e16
6Si
mul
tane
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tele
grap
hy a
nd te
le-
phon
y17
4Si
ngle
cur
rent
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88,,
dup
lex
96 u
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wor
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124
nee
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81c
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124
Skew
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40So
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unde
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89
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d90
Spac
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94H
pagn
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82sp
ark
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133
Spec
ific
indu
ctiv
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paci
ty93
, 107
resi
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, 166
Spur
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res
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nce
92St
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f el
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otiv
e fo
rce
.14,
18
141a
nilit
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85Il
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93in
duct
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162
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s18
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rand
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67fi
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182
Hul
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136
capa
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138
core
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140
elec
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9In
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136
priit
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ater
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f13
7re
sist
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188
tom
pori
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eff
ects
139
test
s du
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layi
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f20
6ii
wor
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spe
ed o
f14
0Su
bter
rane
an c
onst
ruct
ion
188
Supe
rim
pose
d te
leph
one
circ
uit
172
Supp
orts
181
Susc
eptib
ility
41Sw
itch
-spr
ing
test
-bo
x21
2Sy
mm
etri
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wis
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116
125
77,9
1 9227
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63,6
6
Tel
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Ter
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ard,
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one
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the
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thre
e w
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Tes
ting
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and
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tsT
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s m
irro
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e te
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ime
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rans
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Tre
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ell,
The
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nd c
onst
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219
PAG
ESy
phon
rec
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ange
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314
316
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318
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218
921
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219
419
264
, 140 14
020
217
617
117
114
615
717
018
818
9 22 22 22 22 22 21 22 22 .21
2122
, 64 21 21 22 22 22 21 22 22 120
66, 7
0 74
/1w
ires
, joi
ntin
g of
Uni
t mag
netic
fie
ld7
pole
of c
apac
ity,,
of c
urre
ntof
ele
ctro
-mot
ive
forc
eof
for
ceof
qua
ntity
,,of
res
ista
nce
of w
ork
Uni
tsab
solu
teC
.G.S
.de
rive
del
ectr
ical
elec
tro-
mag
netic
elec
tro-
stat
icfu
ndam
enta
lm
agne
ticpr
actic
alU
nive
rsal
bat
tery
sys
tem
shun
tsU
p an
d do
wn
stat
ions
11un
iver
sal w
orki
ng o
f 12
3U
prig
htin
g so
unde
r18
0V
anry
ssel
berg
he s
yste
m17
4V
olt,
The
22V
olta
's c
onta
ct s
erie
s9
Whe
atst
one
brid
ge19
81
fba
ttery
for
200
Wir
es, l
eadi
ng in
181,
187
, 215
num
beri
ng o
f18
7in
cab
le18
9W
irin
g18
5Z
ero
pote
ntia
l4,
72
CIT
Y A
ND
GU
ILD
Sof
LO
ND
ON
IN
STIT
UT
E.
TE
LEG
RA
PH
Y A
ND
TE
LEP
HO
NY
.
SYL
T...
s_A
_BIT
S 19
04-5
.
The
Exa
min
atio
n w
ill in
clud
e qu
estio
ns f
ound
ed o
n su
ch s
ubje
cts
asth
e fo
llow
ing
:-O
RD
INA
RY
GR
AD
E.
1. T
he f
unda
men
tal p
rinc
iple
s of
Ele
ctri
city
in th
eir
appl
icat
ion
to th
eE
lect
rica
l Eng
inee
ring
indu
stri
es.
2. U
nits
of
Mea
sure
men
t.St
anda
rds
ofre
sist
ance
, the
ir p
ract
ical
cons
truc
tion
and
adju
stm
ent ;
ele3
tro-
mot
ive
forc
e an
d ca
paci
ty ;
effe
cts
of te
mpe
ratu
re v
aria
tion.
3. G
alva
nom
eter
s-pr
inci
ples
and
man
ufac
ture
of-
(a)
abso
lute
,(b
)se
nsiti
ve, (
c) c
leld
bea
t, (d
) as
tatic
, (e)
dif
fere
ntia
l.Sh
unts
, ord
inar
y an
dco
nsta
nt r
esis
tanc
e.
4. R
esis
tanc
e co
ils-c
onst
ruct
ion
of ;
gaug
e an
d ki
nd o
f w
ire
;m
etho
dsof
win
ding
and
insu
latin
g.5.
Con
dens
ers-
cons
truc
tion
and
test
ing
of.
6. I
nduc
tion
coils
-con
stru
ctio
n an
d pr
inci
ple
of e
mpl
oym
ent.
7. C
all b
ells
-mag
neto
and
bat
tery
bel
ls; m
agne
to g
ener
ator
s an
d th
eir
cons
truc
tion.
8. I
nstr
umen
ts n
eces
sary
for
the
equi
pmen
t of
an e
lect
rica
l tes
ting
room
-(a)
for
land
line
s, (
b) f
or c
able
s; m
etho
ds o
f us
ing
the
appa
ratu
s in
the
sim
pler
for
ms
of te
stin
g ;
appa
ratu
s re
quir
ed b
y lin
emen
.9.
Ele
ctri
cal t
estin
g as
app
lied
to th
e in
spec
tion
of a
ppar
atus
and
toth
e de
tect
ion
and
rem
oval
of
faul
ts.
10. F
aults
in la
nd a
nd s
ubm
arin
e lin
es ;
thei
r na
ture
and
the
gene
ral
prin
cipl
e of
loca
lisat
ion.
CIT
Y A
ND
GU
ILD
S O
F L
ON
DO
N I
NST
ITU
TE
SY
LL
AB
US
- co
ntin
ued.
11. E
ssen
tial q
ualit
ies
of ir
on a
nd s
teel
for
tem
pora
ry a
nd p
erm
anen
tm
agne
ts r
espe
ctiv
ely
; met
hods
of
mak
ing
perm
anen
t mag
nets
; tr
eatm
ent
of ir
on f
or e
lect
ro-m
agne
ts ;
sim
ple
calc
ulat
ions
as
to th
e ef
fect
ive
pow
erof
a p
erm
anen
t mag
net o
r an
ele
ctro
-mag
net.
12. T
he c
onst
ruct
ion
of te
legr
aph
and
tele
phon
e lin
es, o
verh
ead
and
unde
rgro
und.
13. M
etal
lic c
ircu
it sy
stem
of
wor
king
tele
phon
es a
nd it
s ad
vant
ages
;
indu
ctiv
e di
stur
banc
es a
nd m
etho
ds o
f ov
erco
min
g th
em;
theo
ry o
f su
chm
etho
ds.
14. T
he c
onst
ruct
ion
of s
ubm
arin
e ca
bles
, and
the
sim
pler
of
the
phen
omen
a co
nnec
ted
with
cab
les.
15. T
he s
impl
er s
yste
ms
of te
legr
aphy
wor
ked
by h
and,
incl
udin
g th
edo
uble
cur
rent
dup
lex.
16. B
atte
ries
use
d in
tele
grap
hy a
nd te
leph
ony
;pr
inci
ples
, act
ion
and
cons
truc
tion
;m
etho
dsof
grou
ping
;un
iver
sal
batte
ryw
orki
ng ;
appl
icat
ion
cf s
econ
dary
bat
teri
es to
uni
vers
al w
orki
ng.
17. T
he p
rinc
iple
s in
volv
ed in
the
elec
tric
al tr
ansm
issi
on o
f so
und
and
spee
ch; t
he v
ario
us s
yste
ms
of te
leph
ony
and
the
inst
rum
ents
em
ploy
edth
erei
n, in
clud
ing
rece
iver
s,tr
ansm
itter
s,ca
llbe
lls,
and
exch
ange
switc
hboa
rds.
18. N
atur
e an
d m
etho
ds o
f pr
even
ting
dist
urba
nces
by
eart
h cu
rren
ts.
19. T
estin
g of
mat
eria
ls e
mpl
oyed
in th
e co
nstr
uctio
n of
line
s an
dap
para
tus.
20. M
etho
ds o
f pr
otec
ting
circ
uits
and
appa
ratu
s fr
om li
ghtn
ing
and
from
oth
er e
xtra
neou
s he
avy
curr
ents
.
HO
NO
UR
S G
RA
DE
.C
andi
date
s fo
r H
onou
rs m
ust h
ave
prev
ious
lypa
ssed
in th
e O
rdin
ary
Gra
de.
In th
e H
onou
rs E
xam
inat
ion,
whi
chm
ay b
e ei
ther
in-I
. Tel
egra
phy,
or I
I. T
elep
hony
, mor
e di
ffic
ult q
uest
ions
will
be
set i
n th
esu
bjec
ts o
f th
eO
rdin
ary
Gra
de, a
nd in
add
ition
a k
now
ledg
e w
ill b
e re
quir
ed o
f :-
SEC
TIO
N I
.-T
EL
EG
RA
PHY
.
1. T
he s
yste
ms
of h
igh
spee
d, q
uadr
uple
x, m
ultip
lex,
and
type
-pr
intin
gte
legr
aphs
act
ually
in u
se in
Gre
at B
rita
in.
2. T
he m
anuf
actu
re, l
ayin
g, te
stin
g, w
orki
ng, a
nd r
epai
ring
of
sub-
mar
ine
cabl
es.
CIT
Y A
ND
GU
ILD
S 01
` L
ON
DO
N I
NST
ITU
TE
SY
LL
AB
US
--C
ontin
ued.
3., P
ract
ical
met
hods
for
the
supp
ly o
f cu
rren
t oth
er th
an b
y pr
imar
yba
tteri
es.
4. T
he c
omm
erci
al a
dapt
abili
ty o
f th
e va
riou
s sy
stem
s of
tele
grap
hy.
5. E
xpla
natio
n of
theo
ry o
f th
e W
heat
ston
e B
ridg
e, ta
ngen
t gal
vano
-m
eter
, and
ref
lect
ing
galv
anom
eter
.
6. R
epea
ters
-pri
ncip
les
and
cons
truc
tion;
em
ploy
men
t and
adj
ustm
ent ;
for
sing
le a
nd d
oubl
e cu
rren
t, si
mpl
ex a
nd d
uple
x, a
nd h
igh
spee
d ci
rcui
ts.
7. C
ause
s of
lim
iting
the
spee
d of
aut
omat
ic te
legr
aph
wor
king
, and
.m
etho
ds o
f re
duci
ng th
eir
effe
ct.
8. D
aily
and
oth
er p
erio
dica
l tes
ts in
theo
ry a
nd p
ract
ice.
9. W
irel
ess
tele
grap
hy. SE
CT
ION
1I.
-TE
LE
PHO
NY
.1.
Tra
nsm
itter
s an
d R
ecei
vers
-var
ious
for
ms,
con
stru
ctio
n an
d sp
ecia
lfe
atur
es; a
djus
tmen
t ;m
ater
ials
.
2. T
rans
latio
n fr
om s
ingl
e w
ire
to d
oubl
e w
ire
syst
ems
and
from
cir
cuit
to c
ircu
it by
mea
ns o
f co
nden
sers
and
of
indu
ctio
n co
ils.
3. M
etho
ds o
f w
orki
ng te
leph
ones
and
tele
grap
h in
stru
men
ts s
imul
ta-
neou
sly
on th
e sa
me
wir
e ;
theo
ry o
f.4.
Con
ditio
ns w
hich
lim
it th
e di
stan
ce to
whi
ch te
leph
onic
tran
smis
sion
is p
ossi
ble
;us
e of
iron
and
cop
per
wir
es.
5. I
ndiv
idua
l cal
ls f
or s
ever
al s
tatio
ns o
n on
e ci
rcui
t-th
eory
and
prac
tical
arr
ange
men
t.6.
Exc
hang
e sw
itchb
oard
sys
tem
s fo
r si
ngle
and
for
dou
ble
wir
es.
Mul
tiple
sw
itche
s.
7. S
witc
hes,
Int
erm
edia
te, e
tc.
8. A
utom
atic
Cal
l Box
es.
9. H
ughe
s's
Indu
ctio
n B
alan
ce.
It s
houl
d be
und
erst
ood
that
gen
eral
ly th
e in
trod
uctio
n of
sui
tabl
eill
ustr
ativ
e di
agra
ms
in a
nsw
ers
is to
be
desi
red.
E4e
eleg
rapi
dfd
rani
tleA
ND
4.
4ecn
thet
was
est
ablis
hed
in M
arch
, 189
3, a
nd it
is th
e on
ly te
legr
aph
jour
nal p
ublis
hed
in th
e U
nite
d K
ingd
om.
-±13
+-
Cfr
e &
Leg
al*
gran
itic
is th
e or
gan
of th
e Po
stal
Tel
egra
ph C
lerk
s' A
ssoc
iatio
n,th
e m
ost p
ower
ful o
rgan
isat
ion
inth
e B
ritis
h C
ivil
Serv
ice,
and
is a
lway
s fu
ll of
new
s of
the
grea
test
impo
rtan
ce a
nd in
tere
st to
all
Tel
egra
phis
ts.
ijt -
deg*
6 ra
ni&
devo
tes
spec
ial a
ttent
ion
to te
chni
cal m
atte
rs, a
nd s
ome
of th
e w
orks
now
rec
ogni
sed
as te
xt b
ooks
of
Tel
egra
phy
and
Tel
epho
ny h
ave
firs
t app
eare
d in
ser
ial f
orm
inits
pag
es.
((le
Ect
egra
pt C
4ron
ic1e
is p
ublis
hed
each
alte
rnat
eFr
iday
, pri
cetw
open
ce.
Post
fre
e su
bscr
iptio
n 29
. 6d.
for
six
mon
ths
(thi
rtee
nis
sues
).
Edi
tori
al O
ffic
es: 1
29, P
epys
Roa
d, L
ondo
n, S
.E.
Publ
ishi
ng O
ffic
es: T
he C
o-op
erat
ive
Prin
ting
Soci
ety
Ltd
.,T
udor
Str
eet,
Lon
don,
E.C
.
EV
ER
YD
ESC
RIP
TIO
N°F
GE
NE
RA
L_C
OM
ME
RC
IAL.
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gici
pTIP
PR
INT
1N6
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BY
C9O
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ITO
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1'
TR
ZID
EU
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N15
T5
7' h
e
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NE
W. 9
f'C
9OPE
2IT
IVE
PRIr
`IT
E,1
2,
AN
D A
r
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OR
AT
ION
ST
RE
ET
:.N
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MO
UN
T S
T M
AN
CH
EST
ER
,
RU
TH
ER
FOR
D:S
TN
EW
CA
ST
LE O
N -
TY
NE
IND
EX
.PA
GE
" A
" Po
les
182
Abs
olut
e ga
lvan
omet
er68
units
22, 6
4A
ccum
ulat
or11
8ft
char
ging
of
118
91ch
emic
al a
ctio
n of
117
dist
ribu
tion
of v
olta
ges
126
tiel
ectr
o-m
otiv
e fo
rce
of 1
18fo
rmin
g of
pla
tes
118
resi
stan
ce o
f11
6A
der's
rec
eive
r15
4A
mal
gam
atio
n14
Am
pere
22ho
ur12
5tu
rns
40A
mpe
re's
rul
e89
Ano
de11
4A
rtif
icia
l cir
cuit
95, 1
05, 1
41A
stat
ic g
alva
nom
eter
56pa
ir56
Bal
listic
gal
vano
met
er66
Bat
tery
cel
ls9
bich
rom
ate
18,,
Cla
rk's
sta
ndar
d18
,,D
anie
ll12
grou
ping
of
27.,
Leo
lano
he14
,,se
cond
ary
113
resi
stan
ce, m
easu
rem
ent o
f19
6ft
hal
f -d
efle
ctio
n m
etho
d 19
6,,
dim
inis
hed
defl
ectio
nm
etho
d19
7B
ell t
elep
hone
, as
rece
iver
146
,,as
tran
smitt
er14
5f t
doub
le p
ole
154
Bic
hrom
ate
cell
18, 1
58B
indi
ng18
6B
lake
's tr
ansm
itter
146
Bou
cher
isin
g18
1B
reak
ing
stra
in17
9st
ress
186
Bri
tann
ia jo
int
186
Bur
netis
ing
181
C.G
.S. u
nits
21C
able
s, c
ore
of19
0dr
y co
re19
0 ip
aper
cov
ered
190
test
s du
ring
layi
ng o
f20
6C
apac
ity10
5un
it of
22C
apill
iary
attr
actio
n18
Car
bon
tran
smitt
er14
8te
mpe
ratu
re e
ffec
ts u
pon
148
" C
asca
de,"
arr
ange
men
tof
con-
dens
ers
111,
177
Cat
hode
114
Cel
ls9
aggl
omer
ate
Leo
lanc
he16
batte
ry o
f27
bic
hrom
ate
18C
lark
's s
tand
ard
18
PAG
EC
ells
, con
stan
cy o
f12
Dan
iell
12"
dry
"16
elec
tro-
mot
ive
forc
e of
20, 2
9E
.P.S
.16
6gr
oupi
ng o
f27
in o
ppos
ition
37in
par
alle
l arc
29, 8
0in
qua
ntity
25, 8
0in
ser
ies
27, 8
0el
ectr
o-m
oriv
e fo
rce
of27
resi
stan
ce o
f27
Lec
lanc
h 6
14, 1
58re
sist
ance
of
29, 3
0se
cond
ary
113.
sim
ple
10st
anda
rd14
, 18
sum
mar
y of
19ta
ble
of20
Cir
cuits
72.
artif
icia
l96
, 105
open
and
c.o
sed
74C
lark
's s
tand
ard
cell
18C
lose
d ci
rcui
t wor
king
74C
o -e
ffic
ient
of
mag
netis
atio
n42
Coe
rciv
e fo
rce
6C
omm
utat
or81
Com
pens
atin
g m
agne
t55
, 62
ere
sist
ance
68C
ompo
site
dry
cor
e19
1C
onde
nser
72,,
adju
stm
ent o
f10
9ft
coils
109
grid
141
prac
tical
for
m o
f10
7sh
unte
d14
2tr
iple
109
Con
dens
ers
in "
casc
ade"
111,
177
Con
duct
ivity
, joi
nt52
/9te
st20
1C
ondu
ctor
, con
duct
ivity
of
52fo
r lin
e w
ires
178
mec
hani
cal t
ests
of
179
resi
stan
ce o
f21
Con
duct
ors
join
ed in
" m
ultip
le a
rc"
51an
d in
sula
tors
Con
stan
t of
galv
anom
eter
64re
sist
ance
68C
onst
ruct
ion,
aer
ial
178
Itun
derg
roun
d18
8C
orde
aux
insu
lato
r17
9C
ore
of c
able
189
elec
tro-
mag
riet
43qu
adru
ple
189
Cou
lom
b22
Cre
osot
ing
181,
182
Cro
ss -
over
sys
tem
166
Cro
ss -
talk
164
Cur
bing
cur
rent
142
Cur
rent
, div
isio
n of
54in
duce
d81
tt ft ft ft ff
IND
EX
-co
ntin
ued.
PAG
EC
urre
nt, m
axim
um o
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Dif
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91
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galv
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195
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185
Dir
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er73
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102
tfft
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124
curr
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123
Dou
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89un
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96D
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duct
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163
Dyn
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ft ft IP ft ft
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193
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194
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152
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79, 2
15 40
