WEIGHT. 



In computing tlie foregoing table we have, as on former 

 occafions in this work, reckoned the French metre at 39.371 

 Englifh inches, and the correAnefs of this meafure is of the 

 greateft importance to fcience. It was that originally deter- 

 mined by M . Piftet,in the National Inftitute, by comparing the 

 platina metre with the brafs yard made by Mr. Troughton, 

 which was agreed upon by the Royal Society of London, as 

 the beft medium among our different ftandards, and the moft 

 accurate in its divifions. In making the neceflary deduftions 

 for the etfcfts of temperature on the different metals, Borda's 

 tables of expanfion were ufed ; but from other tables and 

 ftandards different lengths of the metre have been determined ; 

 particularly by Dr. Maf]<elyne, who made it 39.370226, and 

 lately by Capt. Kater, who comes ftill nearer to Piftet, 

 making it 39.37071. But unlefs fuch meafurements are 

 made from the fame flandard yard, and with the fame tables of 

 expanfion, perfeft agreement cannot be expefted ; and then it 

 will be neceffary to determine the important queflion, whe- 

 ther fuch tables and ftandards are quite corre£h ? In fhort, 

 an approximation to perfect accuracy is as much as can be 

 hoped for. It is, however, fatisfaftory to obferve, that the 

 difference between the determinations of M. Pi&et and Capt. 

 Kater is fcarcely difcernible, even in the moit delicate opera- 

 tions of an obfervatory, as it does not amount, when applied 

 in meafuring the pendulum, to more than one-third of a 

 fecond in twenty-four hours. But for all general purpofes 

 the difference is wholly imperceptible. 



This near agreement, therefore, confirms the'propriety of 

 our continuing Piftet's meafure, which is fanftioned by gene- 

 ral ufage both in England and France, and has the addi- 

 tional advantage of numerical fimplicity, which, for com- 

 mercial purpofes, is no flight recommendation. 



Before we enter upon the fubjeft of commercial weight, 

 fome general view ought to be given of the operations now 

 about to take place on the pefidulum in the two hemi- 

 fpheres, as alluded to in our quotation from Laplace. 



The experiments intended by the French, in a voyage of 

 difcovery to the fouthern hemifphere, are to be made with 

 pendulums of an extremely fimple conftruftion, the aftrono- 

 mical rates of which are previoufly afcertained at the Paris 

 obfervatory. In thefe pendulums no maintaining power is 

 applied, nor any compenfation for temperature. The ther- 

 mometer, therefore, and the magnitude of the arc of vibra- 

 tion, muff be continually obferved, and the neceffary cor- 

 reftions applied, as in the experiment of Borda explained in 

 Delambre's Aftronomie, vol. iii. p. 579. Pendulums of a 

 fimilarconftruAion were employed bythe French aftronomers, 

 M. Biot and M. Arago, at the royal obfervatory of Green- 

 wich, and in other parts of Great Britain during the laft year 

 (18 17); but the refult of their experiments has not yet 

 reached us. 



A very correA and beautiful apparatus has lately been 

 erefted at our royal obfervatory, for the purpofe of meafur- 

 ing the length of the pendulum ; and alfo with a view of 

 determining, with extreme exaftnefs, the difference of the 

 force of gravity at Greenwich and Paris, or, in other words, 

 the comparative weight of bodies in thefe two latitudes. 



This apparatus does not very effentially differ from that 

 of Borda, except that a cyhndrical rod of a given length is 

 affumed as a flandard, and the difference between this cy- 

 linder and the whole vibrating fyftem is determined by a 

 micrometer motion given to the fteel table. In the French 



apparatus the fleel table remains fixed, and the meafuring- 

 rod is lengthened by means of a fcrew, till the lower furface 

 comes in contaft v.ith the plane of the table. 



We have hkewile obferved, that in Mr. Pond's appa- 

 ratus, the pendulum of the clock is, by an ingenious con- 

 trivance, brought almoft into contaft with the experimental 

 pendulum, by which the coincidences can be diflinftly ob- 

 ferved with a high optical power. 



In the expedition which has been lately fent by the 

 Britifli government to explore the arftic regions, experi- 

 ments are to be made for fimilar purpofes, but with different 

 apparatus. Two famous clocks, by Shelton, which were 

 ufed by captain Cook, are fent. Each is furnifhed with a 

 new brafs pendulum of an entire piece, which can only vary 

 in length by change of temperature, and this is to be 

 allowed for from conftant obfervation of the thermometer. 

 The rates of the clocks in London have been accurately 

 determined ; and if the fame can be afcertained at or near 

 the pole, the refult will be very important. 



In concluding our view of the philofophy of weight, 

 its varieties on the furfaces of the planets fhould be noticed ; 

 which are determined on the fame principles as on the fur- 

 face of the earth. See Planet, and System. 



The weight of bodies on the furface of the fun is com- 

 puted by Laplace to be about twenty-five times greater than 

 on that of the earth ; without, however, allowing for the 

 diminution of gravity by centrifugal force, which he calcu- 

 lates to be about -j-. See Centrifugal Force. 



Weight, in Commerce, denotes the quantity of any com- 

 modity or fubflance, which is determined by being placed in 

 a fcale againft fome known flandard or weight. The art of 

 weighing is therefore of the utmofl importance, as it fumifhes 

 the befl pradlical means of afcertaiuing the quantity of mat- 

 ter in any given body, and thence the value of mofl of the 

 neceflfaries of life. 



Weights are generally made of flone, iron, lead, brafs, 

 or mixed metal ; and they are moflly flamped by pro- 

 per authorities, denoting that they have been fized or 

 compared with fome known or legal flandard. See 

 Standard, and alfo Measure. 



The weights of aU nations differ from each other, and fre- 

 quently in the fame country a great diverfity prevails. The 

 common denomination is the pound, of which there are 

 moflly two forts, one for weighing the precious metals, and 

 the other for common articles ; fuch are the troy and avoir- 

 dupois weights in England. The former is generally divided 

 into twelve ounces, and the latter into fixteen. But their 

 divifion and multiples, as well as relative proportions, 

 are extremely various. We fhall confider them here under 

 two diflinft heads, viz. Ancient Weights, and Modern 

 Weights. 



Ancient Weights. — From the great importance of 

 weights and meafures, their adjuflments mufl have been co- 

 eval with the firft regulations of civil fociety ; and hence 

 their origin is too remote to be traced by any authentic 

 hiflory. The only ancient weights that are known wirfi 

 any degree of certainty are thofe of the Jews, Greeks, and 

 Romans. 



The ancient Jews, having no flamped coin, weighed all 

 their gold and filver in the following fimple manner, di- 

 viding their talent into 50 maneh, and their maneh into 

 60 fhekels. 



Table 



