26~ TIlE FRANKLIN JOURNAL ANI~

The dying materials chiefly made use of by Mr. Steart~ are, marl= re'ore ba]k, quercitron bark, best blue Aleppo galls, sulphate of iron, ~nd acetate of alumine. A due combination of these materials pro S doces a great variety of drabs, grays, sand-colours, &c.

[3brid. Tran. Soc. ,arts.

On ]~tching and DSng $~'ures on Ivory, at one operation.

From the Transactions of the Society got" the encouraffement ok" Arts, Manufac- tures and. Commerce.

'l'm~" usual mode of ornamenting ivory in black, is to env, rave t h e patte.'n or design, and then to fill up the cavities thus produced, witlx ha,'d b!ack varifish. The demand for engraw~d ivory in ornamented inlayfl% and for other purposes, is considerable, a(though the p r i ce paid for it is not such as to encourage artists of much ability,to devo t e themse!ves to this work, which consequently is trivial ill design a n d coarse m execution. Mr. Cathery 's improvement consists in cm~er- ing the ivory with engraver's varnish, and drawing the design w i t k el{ etching needle; he then pours on a menstruum composed of o n e humlred and twenty grains of fine silver, dissolved in one o u n c e measure of nitric acid, and then diluted with one quart of pure d i s - tilled watec. After haft an hour, more or less, according to the r e - quired depth of tint, the liquor is to be poured ott, and the surthce i s to be washed with distilled water, and dried with blotting p~per; i t is then to be exposed to the light for an hour, after which the v a r n i s h mav~ be ."emove( bye. means, of oil of tm'l)entine. The desio.n~ will n o w appear per,,~anentlv impressed on the ivory, and of a black or b l a c k - ish bvow)l coh)ur, Which will come to its full t int after exposure, f o r a day or two, to tim light.

T[~e property which nitrate of silver possesses, of giving a p e r m a - nent dark stain, to ivory and many other substances, has been lonn. known; but Mr. Calhe@ has the u]erit of having advantazeouslv a n ° - plied it in a department'ol art in which it is likely to be o~ consi~der- able service, by improving the quality of the ornament, and a t t l , e same time of diminishing the cost. Varieties of colour may also b e given by substituting the salts of gold, plafina, copper, &e. for t h e solution°of silver.

Improvement in the manufacture of 3lagnetlc Needles. By Prof. A,~os EATON.

TO mmv. SILLI~IA~.

Sm'Ea,~L years of the early part of my life were devoted % a n extensive land agency, among tile western and rmrthern spurs of t h ~ Catskdl mountains. During this period, I ran most of ~he o u t l i n e s of two hundred thousand acres, beside~ l',tm: tmnpike ,'o~ds acvos.,a

AMERICAN MECHANICS' MAGAZINe, ~(]I,

fhis Alpine dlsh'ict. The difliculfie~ to which I was Mmust daily subjecled, by O~e irregularity of the magnetic needle, were often very embarras.q~. The old surveyors of that time as,sured me, that these fits, as they d~mo;ninated th(~se irregularities, were produced by the action of ma~,~el.ic ores, which they believed abounded in this moun- tainous distri'ct. At one time 1 entertained the opinion, that ! had collected thcts sufficient to demonstrate, that while snow was melth~g away, these [ilS w e r e the most frequent.

Bat ()I, c,,nlp;Mng dill@cut comI)~sses , 1 fi,und that they frequently varied, not only fr(,~ the com|u(;u direction of the maz,{etic needle, but from each other. For example, when set in some (l'ireetions, one compass wouht vary, while other coral)asses would vary when set in different directions~ and would not vary when set in the same direc- tions. On extensive alluvial plains, where we could not suspect the presence of extensive ore-beds, all these dflficulties occurred with equal fi)rce. And what appeared to be a still greater mystery, aa chauging needles, the variation seemed to be governed by the com- pass, not by the needle.

After consideriug every proposed hypothesis, and trying every proposed remedy, ! abandoned the subject, as totally incxplicabie; and contented myself with correcting tl~ese aberrations by ranging back.flags and using two compasses.

While exercising'-fl~e students of Rensse1,~.e.r sch~)ol in land-survey* ing, at the last summer tern,, the same di{tic~fities revived the same enquiries. In a conversation with an im;;enious artist, Mr. Julius Hanks of Troy, l learned that his best compasses had in some in- stances, been subject to those fits of aberratlon, t te showed me.a compass of most elegant and accurate workmanship, with a n o n i u s and double levels, which had been returned by the purchaser on ac- count of the frequency of those fits, I carried this compass to the school with a determination to search out if possible, the cause of its frequent fits. By appiyin~ d,~licately suspended needles, whicll ,night be called a suit of ma~netrometers, I found a point in the lilnb~ wl{;ch attracted a fine needle at the distance of six tenths of an inch. This p~)int, caused the needle belon~;ing to the compass, to deviate at the distance of half an inch on each side; beyond that limit it w~s not affected. Consequently, when the course to be taken, brought the need le wiU;ia that limit, it would deviate, and point accuratclf in all other directions. Any practisinz ~urveyor will readily perceive, that i,~ tracing the li~es around a fieTd, the needle migtlt come within this limit several ti~:~es, or it might not fall within it in runMng a dozen tichl.~. Hence the suppose-d irregularity of the fits.

My co~clu~ious fl'om these experiments were, that a scale from a screw-cutter or a punch, or a teeth from a tile, &c. t,)o minute for flie eye~ might have been lodged in U~at particular point. Cm consult- lug Mr. H~uks, i~e said Ufis might frequently happen, and it was nut imp,'obttble that all those fits complained of by surveyors, migt~t be ~,aced to the same cause; it~asmuch ~.~ nil compass cards att(t ~¢radu.. ated circles were ~,vrouElit~ with very fine steel instrt~me~:ts. 'l't) iilus~

2~z THE FRANKLIN JOURNAL AND

*rate tile subject, I took out the screws fi'om the under side of the cartl, and inserted the point of the fittest sewing needle, less than the twenticth of' an inch in length; whereby I actually produced foul" ad- ditional points of disturbance.

To obviate the difficulty, Mr. Hanks cut off seven tenths of an ineh froln each pale of the needle, ground tile poles to very sharp points, and tipped them with brass caps, extending to the original

• • " T" - - " length of the needle. I his measure, by ~lthdrawmg the magnetic pales froul the sphere of attraction, proved a perfect remedy. M r . l lanks presented tile same compass to the school, where it has b e e n used ahnost daily far two months; anti it is one of the most per fec t instruments that I have ever used. I t has no more lits, and is to ta l ly undisturbed by ma,metic ores~ real or imaginary. Mr. llanks has

< ' 3 • • ~

since correete~l a theodohte m the same way, winch had been thro~v~l aside as useless tbr several years. If the disturbing steel scale is i n tile card neat- the graduated circle, Mr. t[. proposes lengthening t h e pivot aml raising the circle by introducing an additional circle beneath the graduated one. l~lut he has not made this experiment; and i t i s probable no such case will ever occur. For if it were near tile p ivot , it would not disturb the needle; and so little work is required ill t h e card with slender instruments~ that scales will not oRen be left it1 that part.

Another important advantage which will attend tipping n e e d l e s with silver, br~tss, &e. is that of )weserving the points frollt rust. l~t has been demm~strated by concmsive experiments, that m a g n e t i s m resembie~ electricity in acting most powerfully from the s h a r p e s t points. Hence the absurdity of needles made of square bars. H e n c e , a!so. the utility of preserving the finely sharpened points by tips. 1 will add, that, ot' all forms'of needk~s which I have used, the f i a t kinds are best, which are wide in the middle~ and of a trae t aper t o ~he pohtts.

Yours respectfully, A~ros g , l ' o ~ .

l?ensa'cluer ,S~hoo[, T'ro~, N. Y. Nov. 18~26. [ Silliman' s Journal.

C I N C I N N A T I I N 1826.

We have just received a very interesting pamphlet of 100 page .% under the above l:itle, written by B. Drake, and E. MansIield~ t g s ( l s . of that pbtce. The facts which"it details have been collected w i t h great industl'y~ are skilfutly arranged~ and well narrated. T h e 7 t l~ and 8th chapters, which p, resent a view of the populathm atttl mta t l l t - factures of Chlcinnati, we now present to out" readers, anti shall p r e - pare for out" next munber, a general abstract of such other p o r t i o n s , f the work, as may collie most directly w[thia the scope o f o u t - pages.