Reflections on Heat. 179 



From these facts we might conclude a priori, that 

 those bodies which, when warm, give off many calorific 

 rays would, when colder than the surrounding objects, 

 give off to them many frigorific rays. This is exactly 

 what my experiments have made evident to me. 



In experiments made with bodies of the same size, 

 and of the same material, the intervals of temperature 

 being equal, the frigorific influences of cold bodies have 

 always appeared as real and effective as the calorific in- 

 fluences of warm bodies. 



To one of the bulbs of a thermoscope, the tempera- 

 ture of which was 20 of Reaumur's thermometer, were 

 presented at the same time and at equal distances two 

 disks of metal of the same diameter. The .temperature 

 of one of these disks was o (that of melting ice), that 

 of the other was 40. The index of the instrument by 

 remaining at rest showed that the bulb was cooled by 

 the rays from the cold body as much as it was heated 

 by the rays from the warm body. 



If the surface of one of the disks, it matters not of 

 which, is blackened, the intensity of the radiation from 

 this blackened disk is increased to such an extent that 

 the other can no longer counterbalance it ; but if the 

 second one is blackened also, the equality of action is 

 immediately re-established. 



If the emanations from warm and cold bodies are 

 really undulations in an extremely rare and elastic fluid 

 which has been called ether, the communication of heat 

 and cold ought to be similar to the communication of 

 sound ; and all the mechanical contrivances which have 

 been invented to increase the intensity of sound ought 

 to be just as applicable for increasing the effects pro- 

 duced by these emanations from warm and cold bodies ; 



