4>34 Compar'ifon ^ftf^e Definitive Mdre, ^c. 



propntd the following method, which was adopted :— -It 

 coiililled hi tracing out, on a fuiall Hip or rule of metal, of 

 the i a aic thick Of ft; us the Englifh rule, a very delicate line 

 pcrpejvdicular to the length of the rule. This piece of metal 

 was made to red againll a fixed knee, and the microfcopc 

 with fixed threads was brought to the line above mentioned : 

 th£ piece of metal containing that line was then removed, 

 and the metre to be compared was put in its room, with one 

 of ita^:xtreuiilie3 relting againft the fixed knee, and the piece 

 of mictal placed at the other. It is here evident tlr.U the line 

 iraceU out on the piece of metal was in this new pcjfition at 

 the exact diftance of a metre tVom its former pohlion when 

 refting againtt the fixed knee; and, by making the threads 

 of the fecond microfcopc correlpond with this line, the di- 

 ftaoce between the points of interiection of the two tiueads 

 was exattly a metre. To cfiimate the metre in Engliih 

 jnchc"s, nothing then was necelfary but to put into its rooiji 

 the divided rule, to place a line of one of its divifions under 

 that of the interfection of the threads which 'Wa? fixed, aixd 

 to eftipijatx; at the other extremity, by means ot the luicro- 

 jTiiCtcr^ the fraftion of divifion, which witli the whole nuni- 

 J}.er of th.cfe divifions gave the lencth of the metre. 



" The compavifon was repeated on the 4th of Brumaire 

 ft the houfe of one of the connnifiioners by the u)eihod here 

 jdefcribed 5 and after feveral obfervations, which eorref]><mded 

 jjj a very fiitisfaoiory manner, it was found that, at thg tem- 

 peratme of 1275 degree* of tlie centigrade thermometer, the 

 pjatina flandard of the metre was 39*37^ J, aawJ tlie iron 

 ^landard 39'3795 Engliih inches. 



" The two n)Ctres having been confl:rucled to be equal at 

 <.hc temperature of freezing, the operation from which the 

 preceding refuiis were obtained may be verified by finding 

 what the ratios would be at that temperature. For this de- 

 termination we have the correct experiments of Borda, and 

 the connuiffion of weights and meafurcs on the dilatation ot 

 platina, copper, and iron, from which it refidls, that for 

 one degree of the centigrade thermometer, platina dilates 

 0-00000856, iron o'OQooii^^, and copper 0-00001783; 

 and from thefo data it is found that, at tlie temperature ol 

 freezing, tlie plalin.a metre of the InPiitute is equal to 

 '?9-382Bo, and the iron metre to 39'3i>265 Englidi inches, 

 mcafured on thg lUindard of C. Pictet. 



" The difi'erence 000015 between thefe two lengths, lefs 

 than T^-ryS^\ of a line, •or ^^-..'oocth of a metre, may be abfo- 

 tutcly neglected. The refult of our labour therefore is, that, 

 fuppofing the platina and iron Ilandar.ds of the metre belong- 



iiiiZ 



