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 



all in aquiUbrio, A acts as 1, of which * 



P _ - 3 



reflects, 

 B - - iJ 



- - i] 

 diates, I . 



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

 from the thermometers that will be proportion ably altered ; 

 their radiation will remain the same till their own temperatures 

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



A — — "4" I ~ ~ 4 I "" — -*-4T J — — - — ^- I 



reflects, \ radiates, \ sum, [ defect from 2, \ . 

 B - -* f J - - f) - - liJ - - - - fJ 



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 - - II ". - il " -II - " - - -i) 



-s reflects, [ radiates, > sum, > excess above £, f 



(b - - V - - f J - - u V 



But> 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 



