ON TH£ MERIDIAN, 35 



The micrometer head was then turned fo as to bring the wires to a 

 coincidence, and the revolutions of the head and the parts of a revo- 

 lution were noted dovrn. This wa^ done to each of the ten di vifions. 

 and a mean taken, which gave 18 revolutions and 5.0 parts for ihe 

 meafure of ^'^th of an inch. 



The microfcope was then taken to the oppoiite ride of the fcale 

 where every inch is divided into ten parts, and each of thefe being 

 meafured after the above manner, the whole g?5ve a mean of 18 revoo 

 iutions, 50 parts to -/^.th of an inch, Now each of thefe 



INCHES. 



revoluiions is s 20 p:*rts, fa that by aliowrng 28 r. 50 p. to - o 10000 

 Wc have i revolution or 120 parts « - - ^»o°545 



I parr or _.l.Ti-'h 01 a revolution - = » - 0.000045 



This account of the procefs and arrangement being pre.mifed the 

 refuris of the experiments mace on the 2 i ft, 22d and 23! Oclober 

 were as follows : 



Oct, 'Z\?i,-~Onc hundred feet o^ hrsiis meafure was laid off from the 

 fcale in the temperature of 65, i*^ and the ftandard chain was applied 

 at ihe fame temperalure, when the cxcefs oi the chain 



INCI-IES 



above 100 feet of bra fs was 21,3583 r. equf^l - - ..11598 



And fmce 100 feet of brafs expands more than 100 feet of 

 fteel by ,00493 to i*" of temperature, and the chain coin- 

 ciding with the brafs meafure at the temperature of 50^, 

 we have i5°.ix,oo495 inches, or - - - - 0,07474 



Which the chain ought to have fallen fhort, had there been 

 no wear, but as the chain exceeded it by - - 0,11598 



Their fum is, what it has lengthened - - * - 0.19072 



