98 Inquiry concerning the Nature of Heat, 



These researches appear to me to be the more inter- 

 esting, as I have long been of opinion that it must be 

 by experiments of this kind (showing in what manner 

 the temperature of bodies are affected reciprocally at 

 different degrees of temperature and at different dis- 

 tances) that the hypothesis of radiation must be estab- 

 lished or proved to be unfounded. 



When I speak of heat as being communicated to air 

 immediately by a hot body which is cooled in it, I mean 

 only that it is not first communicated to other neighbour- 

 ing bodies, and then given by them to the particles of air 

 with which they happen to be in contact. In this last- 

 mentioned way much of the heat, no doubt, which a hot 

 body loses when cooled in air is ultimately communi- 

 cated to that fluid. 



I am far from supposing that the particles of air 

 which, coming into contact with a hot body, are heated 

 in consequence of that near approximation receive heat 

 in any other manner than that in which other bodies at a 

 greater distance receive it. If in the one case it be gen- 

 erated or excited by the agency of calorific rays or un- 

 dulations caused by the hot body, it must, I am per- 

 suaded, be excited in the same manner in the other. 



The reason why the particle of air which is in imme- 

 diate contact with a hot body is heated, while other par- 

 ticles near it are not affected by the calorific rays from 

 the hot body which are continually passing by them, 

 through the air, is, I conceive, because the particle 

 heated is at the surface of the fluid (air), where these rays 

 are either reflected, refracted, or absorbed ; but when a 

 ray has once passed the surface of a transparent fluid, it 

 proceeds straight forward, without being farther affected 

 by it, and consequently without affecting it, till it conies to 



