Clock (Gnv64)

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A CST PUBLICATION

THE

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BYNAVKALA ROYILLUSTRATEDBYSURENDRA SINGHRATHOREDESIGNED BYSUBIRROY

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6. Atomic clock-

the ultimate

timekeeper

5 Digital quartz

wrist-watch

1. Early man,

recording time by

observing shadows 2 Sundial

4. Portable

timepiece

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T

Miniscule atoms vibrating at 23, 870, 129,300 cycles per second. A radio frequencycharged to match their strength. Trapped in a

mass of pipes, pumps and tubes. Theresult-an explosioh! Or so onewould imagine.All this is just to tell you the time. Time as

recorded by an atomic clock. And time soaccuratethat if you were to go by it, you wouldbe late for school by only one second in

1,700,000 years!

The atomic clock has made man's powersalmostmagical. Today wecan record not onlyevery second but every nanosecond andpicosecond of any occurrence, even theslowing down of the Earth.

Man's need for accuracy and perfection is

not new. Morethan 4000years ago he beganto realize the importance" of measuring time.Earlier, he spoke of events that happened somany 'suns' or 'moons' ago or at the time ofthe 'heavy snows' or the 'big flood'.

In ancient India, just as amonthwas dividedinto thirty days, a day was divided into thirtymuhurtas. (Day and night were taken together).

Distinctive names were given to each of themuhurtas.

Both 'day' and 'night' appeared as naturalunits of time in our earliest literary productions.Expressions like 'many dawns and nights' or'days subdue the nights' occur in the Rig Veda.

The 'ahoratra' (that is, day combined with

night) meant a duration of 24 hours.Aryabhata, one of our greatestmathematicians and astronomers, discussesthe units of time in his masterpiece, theAryabhatiya, written around 500 A.D. In the

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chapterKalakriya Pada, he talks about ayearbeing divided into twelve months; a month into

30 days; a day into 60 nadis and a nadi into60

vinadis. (A nadiwas equalto

24 minutes, avinadi to 24 seconds).Meanwhile, Babylonian priests, fascinated

by mathematics, were making efforts toachieve precise methods that would divideeach day into 24 hours and each hour into 60

minutes.

Those of you who are adventurous, take acue from King Alfred-the Saxon King who

invented the candle-clock.

Candles of the same size, he noticed, burn

down at the same rate. So, Alfred took a

handful of candles, each a foot long, and

The Babylonians noticed that the position of

a shadow changes during the day. So, theyfixed a pole in a sunny place and observed itsshadow as it moved. The shadow, they

discovered, was long at sunrise and graduallygot shorter and shorter until it reached a certainpoint when it began to lengthen again. At

sunset the shadow was as long as at sunriseand at noon it was the shortest.

marked them with a number of bands. Each

band represented a certain division of time,

say, one hour. He could tell how much timehad passed by noting how manydivisions had

burned away.

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Similarly, the Indianswho were studying themovements of the sun, the moon and otherplanets, developed several simpleastronomical instruments like the gnomon,

staff, are, wheel and the armillary sphere.They cast the almanac, that is, a calendar

listing the days, weeks and monthsof the year,calculated on the basis of the movements ofthe sun, moon and other heavenly bodies.

Even as early societies measured the year,the month and the day, they felt the need for

devices that would monitor and indicate timeprecisely. Gradually, one development led toanother and, as with most things scientific,literary or religious, it was an exchange of ideasand achievements between India on the onehand and West Asia and the Mediterraneanworld on the other that produced the so called'first' clocks.

Da Tim

The study of shadows led to the making of

shadow clocks and sundials.

A shadow clock consists ofa length ofwoodwith a crosspiece and a traverse bar whoseshadow marks the passage of the sun, whilea sundial is basically a dial face with a pointerin the centre. The pointer, also known as

gnomon, is a flat piece of metal which pointsnorth in the northern hemisphere and south in

the southern hemisphere. Its upperedge slantsupwards at an angle correspondiAg to thelatitude or the distance that it is away from theEquator. The shadow of the gnomon movesacross a scale around the dial as the sun

moves across the sky.

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ight Time

Shadow clocks and sundials recorded time

during the day, provided, of course, it was aclear, sunny day, but when night came theywere of absolutely no use. That was whenpeople thought of making water-clocks.

A water-clockconsists of a container with asmall hole at the bottom through which thewater can escape. The gradual fall in the levelof the water marks the passage of time. As the

level drops,. it exposes more and more of ascale marked with the hours. To ensure thatthe water drops steadily, the container musthave sloping sides.

The Greeks and Romans used water-clocksfor limiting the time of speeches in the lawcourts. The amount of water put into the

container at the start of a speech dependedon the importance of the case to be argued!Alas! Ifthe winter happened to be too severe,

the water froze and these clocks could notoperate.

Th and Of T"m

As the world progressed, a better method of

measuring time had to be thought of. Areasonably accurate and reliable timekeeperdeveloped was the hourglass.

An hourglass is a particular kind of

sand-glass or 'ghantika yantra' as it wasknown in India. It consists of two glass bulbsjoined by a narrow neck and set in a stand.One of the bulbs contains very fine, dry sand.

To measure the hour, the glass is inverted sothat the sand-filled bulb is on top. Graduallythe sand drains into the bottom bulb and afterexactly one hour the top bulb is empty. Thesand drains at a steady rate, no matter howmuch is left in the top bulb. This method wasquite successful and very soon sand-glasses

were madein

groups of four. There was a1/4

hour, a 1/2 hour, a3/4 hour and an hourglass.That, incidentally, was the origin of the

expression, 'the sands of time are running out'

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Shadow clock Water clock Hourglass

•.-.

If you look at the flowers carefully, you will

notice that some open at 6 a.m., someat 7 a.m.

and others at 8 a.m. Similarly some flowersclose early and some late. So it was that in

19th century England, flowers were laid out in

beds in the form of a clock face. The blooming

or closingof

each bed depicted the hourof theday.

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Ding-Dong

While the sun, the sand, shadows and waterhelped man record the hours, there was still

no sign of a clock that ticked.The exact date of the invention of mechanical

clocks is unknown. The earliest examples,apparently, go back to about 1250A.D. Thesewere based on the massive clock-work modelsthat had been devised by astronomers andmathematicians to study the heavenly bodies.

They were made of wrought iron and wereused atop cathedrals and other buildings. Theregulation of these clocks was clumsyand theywere as much as one hour wrong each day.

By 1389, however, clocks had improvedgreatly. They had bells to ring notonlyon thehour but at every quarter as well.

Strictly speaking, a clock is an instrument

that has a bell and strikes the hours andsometimes the quarters too though we tend to

call any instrument that measuresthe passageof time a clock. Other kinds of time-measurersshould be called timepieces.

Itwas not until the 16th century that clockssmall enough for the. house were developed.

The first movable clocks became possiblewhen weights were replaced by the springdrive. Clocks became the newest and mostexpensive toy in the royal courts. Princes andnoblemen took great delight in organising theirday by it. A banquet would be arranged tobegin at 8 o'clock instead of at sunset andpeople spoke in terms of a place being five

hours away instead of half a day. Thatwas alsowhen 'appointments' were first made.The clock incidentally was thefirst complex

mechanical device to enter the home.

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Around 1660 the pendulum came into use.It was the Italian astronomer, Galileo who

contributed largely to the discovery of thependulum. In 1581, during an earth tremor,Galileo is said to have timed the swings itcaused in a hanging lantern in Pisaagainst thebeats of his pulse. He found that beginningfrom a central point, the lantern swung thesame distance to the left as to the right, in the

same length of time. From this he formed thetheory of isochronism or things performed in

equal times.In 1641 Galileo started applying this theory

to timepieces. He died in the following year.His son Vincenzio continued his father's workand made drawings for pendulum timepiecesin 1649. But he too died without completing a

clock.Finally in 1656, a Dutchman, Christian

Huygens designed the first practical pendulum

clock.

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Despite the discoveryof the spiral spring andthe pendulum, some clocks continued to be

weight-driven. They were cumbersome andugly. So someone thoughht of enclosing theweights and cords in acupboard-like case. Loand behold! the grandfather clock was born.Andwhat astately clock it turned out to be!

Even today grandfather clocks are speciallydesigned for those who like to use it as a

c1ock-cum-furniture piece and bring a bit ofold-world charm into their homes.

1 i i i i i i i i i i i i i i ~ = = = = = = = = = = = = = = = = O

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, pro" Tim'

By this time the value of a clock wasbeginning to be realized by more and more

people. They wanted timepieces small enoughto be carried about.

It was a German, Peter Hele, who made thispossible. He invented the coiled spring whichformed the foundation of all future spring-driven clocks and watches. But the power ofa spring becomes less as it uncoils. So Hele's

timepieces, though unique, were no good astimekeepers. A few years later this problemwas overcome by the incorporation of a deviceknown as the fusee and spring which enabledmore reliable small clocks to be made.

By and by further improvements were madeas people the world over worked on variousmethods of keeping time.

Maharaja Jai Singh II of Jaipur wasmotivated by a strong desire to set up highlyefficient, modern observatories for producingaccurate astronomical data. With the result,

during the early 18th century a large numberof giant instruments, including the Samrat

Yantra (Sundial) were constructed in stone.This was the first time that sundials were set

up in India. Jai Singh constructed severalobservatories. The one at Jaipur is the mostfamous. It has a huge masonry gnomon orsundial pin, whose shadows show the hourofthe day perfectly. New Delhi's 'Jantar Mantar'(observatory) is a big draw.

Jaipur observatory

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Chronometer designedby John Harrison

••

,

Ocean navigations were still controlled by

calculations based on the position of the sun,moon and stars. This inaccurate methodinvariably produced navigation errors becauseeveryminute lost bymistiming could put a shipas much as 15 kilometres off course.

John Harrison of England spent many years

designing a clock for sailors. His fourth attemptproved successful and in 1761 a chronometer

accurate to half a minute ayear was produced.A chronometer keeps time in all variations of

temperature and tells people at sea exactly

how long they have been plying east or west.

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The world gets its time from the sun-a day

being recorded from noon to noon. But, owingto the rotation of the earth on its axis,noontime would differ from place to place. To

avoid this confusion the world has been

divided into 24time zones by imaginary lines,known as meridians. Each time zone is

15 degrees apart and represents a differenceof one hour.

At Greenwich Observatory, England, is the

prime meridian, where Greenwich Mean Time(G.M.T.) is recorded. This is the absolute

standard of time, on which all other times arebased.

When the sun is directly over the prime

meridian, it is 12 noon at Greenwich. At

Inscientific technological work, G.M.T. hasnow been replaced by Coordinated Universal

Time (UTC) which is based on data collectedby Bureau International de I'Heure (BIH),

Stockholm, in the next zone east, it is past

1 o'clock. On the other hand the time zones tothe west of Greenwich are hours behind. New

York, for instance, is five hours behind G.M.T.

If we were to strict ly follow the one hour

difference between each time zone,

especially in a country like India, which

occupies more than one zone, we would have

to adjust our watches while travelling from

Bombay to Calcutta!

Indian Standard Time (I.S.T.) is based on

the meridian which passes through Mirzapur

in U.P. and is 82.5° E of Greenwich. That ishow we in India are 5-1/2 hours ahead of

G.M.T. I.S.T. is maintained and disseminated

by the National Physical Laboratory in Delhi.

Paris. BIH collects data from atomic clocksaround the world and provides an international

atomic time scale which is moreaccurate thanG.M.T.

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165 80

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r10 1 2

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3 4 5 6I

9 10 11 ~ 13 14 15 16 17 18 19 20 21 22

Meridiansshowing 24time zones

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'po zo EI eric ff c ' o nd

It was in 1900 that the possibility oftransmitting electrical impulses from a centralsource to drive clocks was developed. Electricclocks were made in 1918 by Henry EllisWarren, an electrical engineer fromMassachusetts.

The French brothers, Pierre and PaulJacques Curie, had identified the 'piezoelectric effect' in 1880, which meant that

certain crystals vibrate at a constant frequencywhen a controlled alternating voltage is appliedacross them and also that bending or strikingthe crystals produces an electric charge.

In 1929, Warren Alvin Marrison of NewJerseywas the first to applyquartz crystals toelectric clocks.

With this it became possible to measure timespans of a few thousandths of a second.

Today with the atomic clock being used inhigh-speed calculations, all one seems to be

doing is catching up with time!

Day after daytime moves on-not a secondslower or faster than the previous day!

How does this happen? What is it that makesthe hands ofthe clock go round so accurately?

Let us take an ordinary mechanical clock andturn it inside out.

The first thing you do is to wind the clock.When you do this, you are actually winding acoiled spring or the mainspring within the

clock. One - two - 'three - four - round andround goes the coil until it is tight. Butremember, easy does it. For, an extra turnand-snap-the spring goes!

So, you have wound the mainspring justenough and left it. Nowwhat? The coil at oncebegins to unwind. In this way it releases acertain force which drives all the wheels thatactually make up a clock.

But if these wheels just went round andround merrily, it would serve no purpose. Theirmovement has, therefore, to be regulated.

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2 _ . . . . .-+ -

3

•

4

5

Inside a clock

1. Winding key 2. Mainspring 3. Centre wheel

4. Escapewheel 5. Escapement 6. Hairspring

7 Balance-wheel

6

7

The heart of the c10c is the part known asthe regulator. This is a device that controls the

rate at which a clock keeps time. There aredifferent kinds of regulators. The balancewheel is one that is commonly used in mostmechanical watches. This is a delicate wheelwith a pivot at the centre which is connectedto a very fine spiral spring called a hairspring.The hairspring turns the balance-wheel. But

again, not round and round. Its movement isarrested by a lever called a rocker which hastwo pallets. Whichever way the balance-wheelturns, the rocker stops it and the hairspringimmediately pulls it back the other way. Thusthe balance-wheel is kept twisting a half turnone way, a halfturn the otherway. And this isrepeated over and over again. Once the

balance-wheel is set in motion it will move to

and fro in the same length of time.The balance-wheel is connected to a device

known as the escapement which, in turn, is

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The rocker engages one tooth of

the escapewheel and the clock

goes 'tick'

The Escapement

1. Hairspring2. Balance-wheel

3. Rocker

4. Escapewheel

The rockerengages thenext tooth

of the escape wheel andthe clock

goes'tock'.

~ -

connected to the mainspring through a mainwheel, known asthe driving wheel. (I hope youare counting the wheels!)

The escapement consists of a toothed wheelknown as anescapewheel and the rocker (thesame as theonementioned earlier). It has two

jobs. One is to ensure that power 'escapes'from the mainspring. The other, that it

'escapes' at the rate laid down by the regulator,so that eventually the hands of the clock canturn accurately. How does it do this?

We said earlier thatwhen the balance-wheelturns, its movement is arrested by arocker andimmediately the hairspring pulls it back. Thismovement is exactly in step with themovement of the escapement. For, when the

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balance-wheel takes a half turn one way, oneof the pallets ofthe rocker releases atooth ofthe escape wheel and allows it to rotate till itis stopped again by the other pallet. The time

taken by a tooth of the escapewheel to pushaside the first one and then the otherpalletofthe rocker is the time taken bythe clock to gofirst ' tick' and then 'tock'. Thus the clockmoves in a series of jerks controlled by theescapement and the regulator.

Now we have a perfect, isochronic motiongoing. This means, a movement that goes toand fro in the same length of time constantly.This movement has to be transmitted to the

hands of the clock.

ri U

The hour, the minute and the second handmust necessarily go round at different speeds.

Forthis reason theirmovements are controlledby gear wheels.Gear wheels, as you may know, are discs

with teeth cut out of them. These teeth linktogether with the teeth from other wheels sothat, when one wheel turns, the others alsoturn-but in the opposite direction.

If two gear wheels of the same size areinterconnected, theywould rotate at the samespeed. If one of the wheels is half the size ofthe one that it is connected to, the smallerwheel will go round twice in the same time as

the big wheel would take to go round once.The arms ofthe clock work on this principle.

They are thus connected to gears of different

sizes so that they can go round at differentspeeds.

___________________G

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Falling weights were used to power theearliest clocks, especially the grandfather and

grandmother clocks. They worked through aseries of wheels driven by a falling weight on

a cord. The pendulum, which acted as therocker, regulated the rate at which the wheels

turned. The pendulum and escapementtogether produced the 'tick' or forward jerk in

the clock. This was transmitted to a finger that

showed the time.A pendulum is a very good regulator. This is

because the swings or oscillation:;; of apendulum are regular and steady. You can seethis for yourself if you tie a weight on a piece

of string and allow it to swing back and forth.

The Pendulum

4

3

5

< ~ U I r - - - - 2

1. Rocker 2. Escapewheel

3. Pendulum rod 4. Bob

5. Weignt

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E c ron" CI c

While the method of working remains thesame for all modern clocks, the material used

varies. For instance, in research laboratoriesand for astronomical observations two

extremely precise kinds of electronic clocksare used today. They are the quartz crystalclock and the atomic clock.

Quartz is one of the commonest minerals.Sand is made up almost entirelyof small grains

of quartz. Usually it is milkywhite or has shadesof various colours, but sometimes it is as clear

as glass. This form is called rock crystal. In

bulk form quartz is crystalline..Pure quartz has interesting electrical

properties which make it suitable for regulatingthe mechanism of a clock. When an electriccurrent is passed through a quartz crystal, thecrystal vibrates atan almost perfectly constantrate. The rate of the vibration depends on the

thickness of the crystal. The thinner it is, thefaster it vibrates. The faster it can be made to

The front ofa quartz

crystal clock

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The atomic clock is the most accuratetime-keeping machine to date. It can measure

time intervals of a millionth of a second. It usesthe vibrations of either ammonia or caesiumatoms as a regulating device. These atomsvibrate very regularly and rapidly-thousands

of millions of times every second. .The principle of the atomic clock was

worked out in 1946 by the American physicist,

Dr. Willard Frank Libby. The first such clockwas made two years later at the NationalBureau of Standards in Washington D.C. In

1969 the U.S. Naval Research Laboratory builtan atomic clock, counting the oscillations of

the ammonia atom. The National PhysicalLaboratory at New Delhi, has five caesiumatomic clocks.

To look at, the atomic clock is nothing likean ordinary clock. It is a complicated mass oftubes, pipes, pumps and electronic gadgets.A radio frequency is charged to match the

vibrate, the smaller is the time interval that canbe measured.

In a quartz clock the crystal is made so thinthat it vibrates 1,000,000 times a second. This

makes it possible to measure time intervals ofa few thousandths of a second.

At major sports tracks events are filmed anda quartz-crystal timing mechanism in thecamera runs all through the race. It directs thefigures through a prism on to the film to givesplit-second timing of the finish.

A quartz crystal clock can have a dial ordigital face. The battery makes the crystaloscillate at its natural rate. A divider circuit in

the watch converts the natural vibration rate toone pulse per second. A motor converts thesevibrations into one-second 'ticks'. These aretransmitted to the clock face again by a set ofwheels.

t Of Tim

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.. -- Theatomic beam chamberof a caesium atomic clockL . . - - _ ~ - { ] - - - - - \ 7 - - - - - - - _ - - Istrength of the atom that is used. The radiofrequency (maintained at the correct rate by

constant electronic checking) makes the clockadvance one second after the number of

vibrations has been counted off electronically.Atomic clocks are used for high-speed

navigation calculations an9 by advancedresearch scientists and astronomers.

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For the rest ofus there are a variety of clocks

available these days. Aside from mechanicalclocks there are those that run on electricity.Some of them merely use electricity as a

source of power to drive the clock mechanism.In some battery-operated ones, the electricitypowers a small electric motor which rewindsthe mainspring of theclock every fewminutes.In large public clocks electricity is used to

power amotorwhich winds up aweight drivingthe clockwork.The most common electric clocks, however,

use electricity not only to power them but alsoto regulate them. They arecalled synchronousclocks. In these clocks the motor driving themechanism keeps in step with the rapid

alternationof

the electric current.And if you attempt to listen to the 'ticks' in

an electric clock, you will not be able to hearthem, because an electric clock has no'tick-tacks'. It has no rocker and no hooks. A

8

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Electric clocks

small electric motor turns the wheels and thewheels turn the hands. As the electric motoralways runs at the same speed the hands of

the clock point to the right time without the'tick-tack' sound.

tTlo

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Many of us have come across deligh fulclocks that chime or say 'cuckoo' and

wondered how they work. At times one haseven been tempted to go behind the 'cuckooclock' and see if there is a real bird in there!There are actually two whistles that make

the 'cuckoo' sound. Little boxes, calledbellows, blow air through the whistles. If youlisten carefully, the first 'coo' is shorter thanthe second. The twowhistles tooting, one afterthe other, make the 'cuckoo' sound.At one o'clockthe clock 'cuckoos' one time.

At two o'clock two times and so on. Whatmakesthe clock 'cuckoo' the right numberoftimes?A catch flips out of a notch in a special wheel

when it is time for the clock to 'cuckoo'. The

wheel turns a short way, the little door popsopen, the bird comes out and bows and thewhistles go 'cuckoo'! As long as this wheelturns, the clock 'cuckoos' overand overagain.

Thewheel turns when the catch is out of thenotch. The catch slides on the edge of theturning wheel. The wheel stops when the catchfalls into the next notch. With that the 'cuckoo'

sound also stops.

A cuckoo clock

'cuckoos' on the

hour

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From themoment the alarm clock wakes usup we know it is one mad rush-to catch the

bus, to school, to work, to get back home, toplay and to sleep. All this must bedonewithin

the 24 hours we have allotted ourselves eachday.It is not surprising then that people discard

their watches to counteract the pressure of

work when they want to go away to a quietplace on a real holiday!

When we say a clock has jewels, whatexactly does it mean?The moving parts of a watch, that is, the

escape wheel, the balance-wheel and so onturn in bearings often made of jewels. Such

bearings, called jewelled bearings, are used

because they are hard and can withstand yearafter year of constant use. So next time yousee a watch that claims 17 jewels, don't look

puzzled!

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This book, one of a series of informationbooks, introduces the child to a variety of

clocks-ancient and modern. It explains in

a simple manner how the clock works.

Others in this series include:

• TheTelevision

• The Telephone• The Mator Car• The Aeroplane• The Ship• The RailwayTrain• The Computer

@by CBT 1988Reprinted 1990, 1993, 1995, 1997, 1999, 2001, 2003, 2004, 2006.

Published by Children's Book Trust, Nehru House,

4 Bahadur Shah Zafar Marg, New Delhi-110002 and

printed at its Indraprastha Press. Ph: 23316970-74

Fax: 23721090 e-mail: [email protected]

Website: www.childrensbooktrust.com

- -------- ----- ------ --- --- - - -ISBN 81-7011-398-9

788170113980

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