182 ON THE RADIATION OF CALORIC. 



much caloric. This reasoning will be much confirmed, by 

 considering the circumstances which will occur, when the sur- 

 face of the thermometer is supposed to be changed. Fig. 5, 

 let P be a thermometer with a surface of polished metal, and 

 B a blackened thermometer, and their radiating and reflecting 

 powers as above. Let A be any body. Then while they are 



fP - - I] -. - il 

 all in (Bquilibno, A acts as 1, of which -J reflects, > radiates, J. 



IB - - iJ - - iJ 



Now, if the temperature of A be changed, it is the reflection 

 from the thermometers that will be proportionably altered; 

 their radiation will remain the same till their own temperatures 

 are changed. Let A be heated till its action is as 2. Then, 



- - II -. - il - - If] - - - - i] 

 reflects, > radiates, > sum, > defect from 2, > . 



- - fJ - - fl - - I*-' - - - - JJ 



But it is this last quantity, namely, the difference between the 

 action of the thermometer and that of the heated body, which 

 operates to raise the temperature of the thermometer ; and 

 therefore, that with the blackened surface will shew 3 times 

 the sensibility to heat that the polished one does. 

 Next let A be cooled till its action is as |. Then, 



(P - - 11 - - il - - 11 i) 



■s reflects, > radiates, > sum, |> excess above |, >■ 



vB- - i' - - sJ- -iJ - - - - -f-' 



Bub it is this last quantity, the difference between the action 

 of the thermometer and that of the cold body, which affects 

 the temperature of the thermometer, and therefore the black- 

 ened 



