the new-york exhibition illustrated.

ere long require the decision of this point, and in that case Eater s ®®®°” " Pdulum at Paris ought to have a standard relation to the metre posrtively estab-lished, so that original standards can be made without stint or res n ®property of the pendulum which Huygens demonstrated, t a 1 s. een "

pension and oscillation are reciprocally convertible, and Katei s simp eweight, by which the pendulum can be brought to oscillate u ®* 0 ? e< L, r , I . p<!en twhen suspended in turn on the two opposite knife edges, w ic ^ enthese centres; these together, give a most exact means of determiningof the seconds pendulum, which length for the same locality is a so

But the merits of the several natural units became a foregoneAcademy Commission, when they had decided to use the qua ran o t m -j’and to make the fundamental standard unit of metrology, equa olionth of this quadrant. When the metre had thus been adopte , ®

Commission was marked by every excellence, and its execution 6 n

highest energy and enthusiasm, especially on the part of those metre

who measured the arc whence the final metre was derived. P adopted

deduced from the Peru arc measured by Bouguer and La Con a ™^ e, -w-^ c ] ia j n an qfor use during the great arc measurement, specially execute yDelambre; an arc prolonged by Biot and Arago to the Island of Fo ^

the South, and by Gen. Boy to the Isle of Wight on distlir bances

results of this measurement so triumphantly consummated a . Weights andof the Eevolution, had been properly shaped, a new Commission ot ^

Measures was constituted, embracing a long array of distinguis e ^ ’. g ftgfrom France alone, but from several other European states. _ j, a .

follows: Berthollet, Borda, Brisson, Coulomb, Darcet, De am re, n( j’y angrange, Laplace, Lefebvre-Gineau, Legendre, M6chain, Monge, ron pjenchdermonde, members of the Institute of France; Lenoir an ° ’ g a jbi

instrument artists; Anae and Yan Swinden from the Batavian epu ,

from Sardinia; Bugge from Denmark; Ciscav and Pedray^si romfrom the Tuscan Republic; Franchini from the Roman Be P u . ’ Ues frora

from the Cisalpine Republic; Multedo from the Ligurian Repuic, -^ eun j er

the Helvetic Republic; and Yassali from Piedmont: Lavoisier, 1 ®were also associated. This Commission proceeded from the ma eria w ]dchto frame a thorough, unibasal, universal, and decimal system o me i

system was both legally and practically adopted. velv to

The metre or unit of length is multiplied and divided by e ^ ’ for

give the other denominations of length, Latin numeral pre xes _

the submultiples, and Greek ones for the multiples in forming nam ,

'« faW. hundred, » fcr . tt.ue.nd,

(0,1), one-tenth, centi for (0,01), one hundredth, milk fo ( , L cent ilitre, andThese prefixes are used with all the basal units, thus. cen ’ ^ Qr wood

centigramme. The are or land unit is ten metres square . ^ and

measure is a cubic metre. The litre or unit of capacity measure ’ m or un itliquid, is one-tenth of a metre cubed, or a cubic decimetre. water a t its

of weight, is the weight in vacuo of a cubic centimetre o „ nT1 fains five

maximum density, or 4° centigrade. The franc or monetary uni ’ ^ach

grammes of an alloy composed of nine parts of silver an ° ne ° tJ]e kilometremultiple or submultiple can be used as an independent uni . . meagure -

»th. uni. 1. counting road di.ttnc., ft. »!!«».« "T.ti.

ments, and the kilogramme for commercial weights. ^ an( j usa g e onlyprefixes have only become usage for the metre, lltre an S™? ’ , the een tutere

derives the hectere and the centiere from the a/re ; the eefrom the stcre ; and the decime, and the centime from , , oornpu tations

This system, so systematical in its parts, and so we a ap bag ever

and ordinary convenience, is certainly far better than any °^ i Tin . vfirsa] _ and

—v/iuiutti j vauvuvv) —j — i-»v a universal and

existed. It was framed in the high hope that it wou ^indefinable units,that it would put an end to the chaos of incommensura e a nniversal, it iswhich has too long harassed the world. If any system ® c0 ® systematic

clearly destined to be this one, for no other which prevai s tba t this

merit, or is even entitled to be called a system.. ts Already it has

consummation is not to be wholly despaired of in t e u u orn fi a rdy, Mo-been legalized in Spain, France, Belgium, Switze:rlan , c i an , doptec i a

fiena, Piedmont, Poland, and Greece, while the Zollverem States ^na i ^

modification of the metre system. On our own con men , ’ - c0 _ Thus far

vails in Chili and Columbia, and has recently been a op e r w j tb tfi e

bas it progressed: the question now is as to its ^ e n ^eZn^er how corn-sturdy and conservative Anglo-Saxon nations. rendering more sensible

merce is yearly multiplying international con ac s, ^ _ t geemg not en tirelythe inconveniences arising from manifold units ’ be mo llified into

impossible that in some way, our generic se 0n the other hand,

a final conformity, so conducive to practical con ' nations w jll but add

this very extension of weighing and measuring a s inconveniences

to the resistance which must always be excited by

Zt - 01 u— >» «

ernmont to that of France, France presented to the United States in 1852, a fullset of her standard measures of length and capacity, weights and balances. M.A. Vatembre made himself active in procuring the interchange. This presenta-tion embraced a complete collection of all the apparatus, weights and measuresbelonging to a bureau of verification; a brass metre, litre, and kilogramme, byGambey, and finally, a standard steel metre prepared and verified by Silbermannwith the utmost care. Our space prohibits detailed references to the numerousitems included in this gift, and we must be content with a brief discussion of Sil-bermann’s metre, now at the Crystal Palace. This was laid off and compared bya new process and comparing apparatus of Silbermann’s invention, which cer-tainly possesses peculiar merit. It gives botli a line and end measure standardmetre, and the comparison with the conservatory platinum standard of Francegives for its length raO.9999774. There is, however, reason for questioning thepresent accuracy of the two prototype metres of the State and Interior Depart-ments of France. They were made from platinum, worked witli the aid of mer-cury, which was supposed to have been wholly driven off by heating, but whichis now suspected of having left a trace of mercury in the body of the bar, suffi-cient by its slow transfusion and evaporation to have produced a change ofstructure and of length. One is also slightly bent, and altogether, they are perhapsless trustworthy than their ruder iron contemporaries. One of the iron metres whichTralles retained from those made under his charge for distribution to the severalmembers of the great Commission, was presented by him to Mr. Ilassler and isnowin the U. S. Department of Weights and Measures, though it is the propertyof the Am. Phil. Society. This is doubtless a higher authority than Silbermann’sor the Treasury platinum metre, and we may look for some farther light on thecondition of the two platinum prototypes, from a careful pyrometer comparisonbetween the Silbermann and Committee metres.

Notwithstanding the ingenuity and ostensible delicacy of Silbermann’s compar-ing apparatus, it seems to us not equal to Saxton’s pyrometer, a specimen of whichvery perfect instrument is now at the Crystal Palace. Silbermann’s comparing ap-paratus professes to appreciate one ten-millionth of a metre (not the one-hnndred-thousandtli, as stated by Nickl5s, in the January No. American Journal of Science-see his accounts in January and May Nos. 1853). Saxton’s pyrometer is now so ar-ranged that one-twenty-five-thonsandtli of an inch is magnified into a unit of gra-duation about one-fourth of an inch long, from which the one hundred-thousandthof an inch, or about one four-millionth of a metre is easily read, and this readingcould, with perfect facility, be made much more minute, if desired. Whitworth’smachine, which reads to millionths of an inch, is not adapted to long bars, andinvolves some liabilities to incidental errors, peculiarly unfitting it for verifyinglength standards. The truth is, that the minuteness of reading is no criterion of' positive practical accuracy, for this is contingent on numerous other circumstan-ces of condition. It is because the minimum reading in Silbermann’s arrangementquite exceeds the probable degree of correctness in magnifying the motion and inappreciating disturbing causes, that it is liable to be over-estimated in respect toprecision. In Saxton’s pyrometer the magnifying of minute variations in lengthis effected in a simpler and more reliable manner than in any other arrangementnow known to us, and it presents the advantage of being applicable to bars of anylength, and of removing the observer to such a distance that the heat of his bodyis not a sensible disturbing cause. The rotating mirror is a peculiarly felicitousdevice, which unites nearly all desirable elements for experimenting on the dilata-tions and contractions of bars. Its use in comparing and verifying the bars forCoast Survey bases, has deservedly established it as a special favorite on accountof its united delicacy and convenience. Large experience in its use has not indi-cated any advantage from increasing its minuteness of subdivision for readingsInappreciable changes of temperature affect it sensibly with a bar six metros longwhen indeed it becomes the most sensitive of thermometers. The pyrometerhas been the means of leading to a more perfect compensation for temperaturevariations in the Coast Survey base apparatus, than could have resulted from theuse of any other means now known. It also affords the best index of the accu-racy of this compensation in each base measuring tube. It is only applicable toverifying end measures. For engraving and comparing engraved lines on stand-ards, the arrangement of Silbermann seems worthy of great reliance, as isTroughton’s also.

The workmanship of the French weights, measures, and balances is not gene-rally of that high order which might have been anticipated, though this fact willexcite no great wonder, when it is known that all these articles are made by con-tract, and not in a government establishment. The standards for ordinary com-mercial verifications are only capable of insuring moderate accuracy, though forthe purposes intended, this is doubtless adequate. There is in these standards acertain rudeness of aspect quite surprising to American eyes, for it cannot bedoubted that in tools, implements, and utensils, American mechanics have a higherappreciation and a quicker sense of fitness, convenience, and artistic expressionthan is to be found in any other country. The French standard wood sheet-ironand tin measures of capacity for commercial verifications, are hardly equal in styleto the commonest buckets in our market, and the balances corresponding have asingular clumsiness of construction. The routine life of old communities, prevents