and the Mode of its Communication* 85 



of 10 degrees (namely, from the point of 50 degrees to 

 that of 40 degrees above the temperature of the air of 

 the room) in 33 minutes and 42 seconds ; whereas 

 the other vessel, which was not over ice, required 39 

 minutes and 15 seconds to cool through the same in- 

 terval. 



Experiment No. 30. On repeating this experiment 

 the next day, the air of the room still remaining at 63, 

 the times of cooling through the given interval were as 

 follows : 



Min. Sec. 



The vessel suspended over the ice-cold platter, in . 33 15 

 The other vessel, in 39 3 



From the results of these experiments (which were 

 made with the greatest possible care) it appears that 

 the radiations of cold bodies act on warmer bodies at a 

 distance^ and gradually diminish their temperatures. 



It will likewise be evident, when we consider the 

 matter with attention, that the cooling of the vessel 

 which was suspended over the ice-cold platter was in 

 fact considerably more accelerated by the frigorific radia- 

 tions from that cold surface than it appears to have 

 been when we estimate the effects produced simply by 

 the difference of the times taken up in the cooling of 

 the two vessels, without having regard to any other 

 circumstance. 



These times are, no doubt, inversely as the velocities 

 of cooling ; but, as all the heat lost by the vessels dur- 

 ing the time of their cooling did not pass off through 

 their flat bottoms, and as the rays from the cold sur- 

 face fell on the bottom only of the vessel which was sus- 

 pended over it, without at all affecting its covered sides, 

 the velocity with which the heat made its way through 



