270 Mr. Dauiell on a New Regislcr-2^j/rometcr, 



Table III. 



1°17' = -01119 

 1 23 = -01206 

 1 16 = -01105 

 1 23 = -01206 

 1 20 = -01163 



1 23 = -01206— Mean 1° 20' = -01163. 

 The temperature of the atmosphere was about 64'° during 

 these observations. 



Exp. 2. A bar of soft iron, of the same dimensions as that 

 of platinum, was substituted for the latter in the register. The 

 experiment was repeated five times ; twice with the register 

 immersed in the mercury, and three times exposed only to the 

 vapour. The time of exposure varied from twenty minutes 

 to ten, from the first moment when the metal began to boil. 



The following Table exhibits the several readings and the 

 appropriate expansions. 



Table IV. 

 2° 13' = -01933 



2 33 = -02224- 

 2 10 = -01890 

 2 23 = -02079 



2 20 = -02036— Mean 2° 20' = -02036. 

 The greatest variation from the mean was therefore only 

 __ 6__(iths of ail inch in the platinum experiment, and 



To!(Joo^^^^ in the iron. 



We shall now compare these results with the preceding 

 determinations of MM. Dulong and Petit. 

 The Expansio7i of Platinum. 

 Length of Bar. 



From 32° to 212° = -00088420x6*5 =-00574.7300 



From 392° to 572° = -00091827 X 6-5 ='005968755 



•011716055 

 From 212° to 392° = Mean of the above . ... =-005858027 



Total expansion from 32° to 572° =-017574082 



Add for the expansion from 572° to 660°, 

 the temperature of boiling mercury, calculated 

 at the highest rate : — 



180°: -005968755 : : 88° : •002918058 . ... =-002918058 



"^0492140 

 Deduct expansion for 32°, the experiment witli 



the pyi'ometer having been made at 64° ... =-001021742 

 Calculated at the lowest rate : — 



180° : -005747300 : : 32° : -001021742 

 Real expansion of the bar by Dulong and Petit =-019470398 



Tf 



