Expansion and Contraction of Building Stone. 139 
tric state of the stone was not recorded, we can take no account of 
it in our deductions.. These discrepancies, however, will have but 
little effect upon the general result ; for it will be observed, that there 
is always an increase in the length of stone for an increase of tem- 
perature, when any two experiments are considered which are re- 
moved from each other by several degrees. 
From the facts ascertained concerning the expansion of other sub- 
stances, we may assume that the expansion of stone is uniform, and 
that, within the range of our experiments, each of the stones increas- 
ed in length by a common difference for each degree of the ther- 
mometer. ‘To find an approximate value for this common differ- 
ence, say for the granite, we subtract the first observed length from 
the last, and, if these experiments were accurate, the difference 
.0470, would be ninety six times the common difference ; ninety six 
being the difference in degrees between the extreme temperatures : 
the same operation being performed with the second experiment, 
and that next the last; the difference .0298, (the difference in 
lengths,) should be eighty six times the common difference. 
thus comparing the extreme experiments of those which remain, we 
obtain the following table. 
Experiments. pac Diff. in lengths. 
14 and 18 16 — .0034 
15 and 17 il — .0034 
Total, | 817 3708 
have the least weight in determining the common difference. 
