408 ME. W. HOPKIXS OX THE COXSTEECTIOX OE A XEM" CAEOEDIETEE. 
Sandstone (building stone). 
Q=8-882«V-l)+-03720 
Polished Limestone. 
Q= 9-106 a%a^-l)+ -03720 . 
Unpolished Limestone (same block). 
Q= 12-808 («'-!) + -03720 (^.^yV^^ 
The approximate equality of the different values of Q for these substances under 
similar conditions, is what would have scarcely been anticipated. The value of Q. 
however, for the surface of silver, as shown by Duloxg and Petit, is very much smaller 
than the preceding values. Such appears also to be the case ■s^ith mercun' and polished 
steel. But in this last case the surface of the steel and its radiating power are affected 
by high temperatures, at which also an amount of vaporization takes place from the 
surface of mercury, which affects the indications of the instrument. 
