for Measuring the Expa7isio7i of Solids. 199 



The expansion of Copper. 

 Length of Bar. 



From 32° to 212° = •0017182x6-5 =-01116830 



From 392^ to 572° = •0018832x6-5 = -01224080 



•02340910 

 From 212° to 392° = Mean of the above = -01170455 



Total expansion from 32° to 572° = -03511365 



Add for the expansion from 572° to 660°, the 



temperature of boiling mercury, calculated 



at the highest rate : — 



180°: -0018832:: 88°: -00920675 = "00920675 



•04432040 

 Deduct expansion for 32°, the experiment with 



the pyrometer having commenced at 64°.... = -00305457 



Calculated at the lowest rate : — 



180: -0017182: : 32°: -00305457 f 



Real expansion of the bar by Dulong and Petit = '04126583 



If from the real expansion thus obtained -04126 



we deduct the apparent expansion obtained by the 



pyrometer -03633 



The remainder -00493 

 will be the expansion of the black-lead. ~ 



We thus obtain the expansion of 6-5 inches of 

 black-lead ware, 



from 64° to 660° by platinum bar -00421 



by iron bar -00457 



by copper bar -00493 



Mean -00457 

 in which the extreme results differ from the mean not -0004 

 inch, or one-fourteenth of the whole. 



When we take into consideration the great difference in the 

 total expansion of these three metals, as well as the differences 

 in their several rates of increase with the increasing tempera- 

 ture, such an accordance appears to me to be perfectly deci- 

 sive of the accuracy of the pyrometer. 



It will be unnecessary for me to trouble the Society with 

 the details of the experiments by which I determined the ex- 

 pansion of several other metals to the boiling point of mer- 

 cury; it will be sufficient to state the results in a tabular form. 

 I thought that it would add nmch to the interest of the de- 



