FOR MEASURING THE EXPANSION OF SOLIDS. 
445 
The expansion of Copper. 
Length of Bar. 
From 32° to 212° = .0017182 X 6.5 =.01116830 
From 392° to 572° = .0018832 X 6.5 = .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 
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 0042 1 
by Iron bar 00457 
by Copper bar 00493 
Mean .00457 
in which the extreme results differ from the mean not .0004 inch, or one four- 
teenth 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 
