WITH THE ENGLISH STANDARD.. 249 



thus fixed, the graduated fcale was transferred ; one of the 

 divifions was placed exactly under one of the micrpfcopes, 

 and the micrometer fcrew was turned in order to meafure the 

 fraction, exprefling the diftance of the other microfcope from 

 another divifion. 



The comparifon was repeated in the fame manner the 4th Precife refult at 

 Brumaire (26th Odober laft) at the houfe of one of the Com-^ t# ofF ' hrcn " 

 mittee, and after feveral experiments, agreeing very fatisfac- 

 torily with each other, it was found that at the temperature 

 12.75° centigrade, or 55° of Fahrenheit, the ftandard of pla- 

 tina was 39.3781, and that of iron 39.3795 Englifh inches. 



The two metres being conitru£ted to be equal at the tempe- Reduction to the 

 rature of melting ice, thefe operations may be verified by re- ten ? p . erat . ure of 

 ducing their refults to that temperature. For this determina- 

 tion we are provided with the accurate experiments made by 

 Borda, and the committee of weights and meafures, on the 

 dilatation of platina, brafs, and iron ; from which it appears, 

 that for every degree of the decimal thermometer, platina ex- 

 pands .00000856; iron .00001156; and brafs .00001783; 

 (for Fahrenheit's fcale thefe quantities become 476, and 642, 

 and 990 parts in an hundred millions.) From thefe data we find 

 that, at the freezing point, the ftandard metre of platina was 

 equal to 39.38280, and that of iron to 39,38265 Englifh inches 

 of M. Pi&et's fcale. The difference is lefs than the 500th of 

 a line, or the 200000th of the whole metre, and is therefore 

 wholly inconfiderable. 



The refult of the whole comparifon is therefore this. Sup- Standard metre 

 pofing all the meafures at the temperature of melting ice, each at 3 * ls — 

 of the ftandard metres is equal to the 10000000th part of the lift inches. 

 quadrant of the meridian, and to 39.38272 Englifh inches of 

 M. Pidet's fcale. 



At the clafs of mathematical and phyfical fciences of the 

 National Inftitute, 6 Nivofe, year 10. 



Legendre, Mechain, and Prony, Reporter. 



This report is approved, and its conclufions adopted by the 

 clafs. Certified in conformity with the original by Delambre. 



Paris, 26 Nivofe, year 10 (16th January, 1802). 

 [The reft of this Paper if by the learned Secretary to the Royal 

 Inftitution, Dr. Young.] 



On examining the reduction of the ftandards of platina and Revifion by Dr, 

 iron to the freezing point, it appears that they differ fomewhat Youn S» 



lefs 



