272 
MR. DANIELL ON A NEW REGISTER- PYROMETER 
Table YII. (Continued.) 
Expansion of the Metal Bars. 
Expansion of 
Black-lead Register. 
Difference from Mean. 
Lead 
. . . absolute .01542 
apparent .01223 
. =.00319 . 
. +.00085 
Brass 
. . . absolute .01045 
apparent .00/99 
. =.00246 . 
. +.00012 
Gold 
. . . absolute .00794 
apparent .00552 . 
. =.00242 . 
. +.00008 
Silver 
. . . absolute .01034 
apparent .00814 
. =.00220 . 
. -.00014 
Mean .00234 
In five instances out of these nine, the difference of the expansion of the 
black-lead from the mean does not exceed j— ^dths of an inch, two being in 
deficiency, and three in excess : and it is worthy of observation that they are 
the metals whose dilatations have always been considered the most regular, 
and concerning which there is the least difference of authorities, viz. gold, 
silver, platinum, copper, and brass. The greatest difference is in the tin, 
which amounts to nearly j^dths of an inch in excess ; and it is more than 
probable that the absolute expansion of this metal has not hitherto been 
obtained with sufficient precision, and that it even varies in different states. I 
shall return to this subject in the second part of this Paper, which I reserve 
for a future communication ; in which I hope to be able to lay before the 
Society observations and tables of the dilatations of metals to their melting 
points. It is my intention in this first part to touch no further upon the 
subject of expansion than is sufficient to establish confidence in the pyrometer 
as a measure of heat. 
Another confirmation of the precision of these observations may be derived 
by calculating the expansion of the black-lead register for the 150°, from the 
greater expansion previously determined by the boiling point of mercury for 
590° : .00831 : : 150° : .00209 
which only differs i0o %dths of an inch from the above mean. 
