244 On th e Cooling of Liquids in Vessels 



however, very easy to hasten materially the heating of 

 the liquid in this case ; all that is necessary is to begin 

 by blackening the outside of the coffee-pot over the 

 flame of a candle or of a lamp, or to destroy or conceal 

 in some other way the metallic lustre. 



All the facts which I have just detailed are easily 

 explained, and, to my mind, satisfactorily, by the theory 

 of heat developed in the various memoirs on this sub- 

 ject which I have had the honour of presenting to this 

 Assembly at different times. 



If heat is nothing but a vibratory motion of the par- 

 ticles of a body, a motion which always exists in all 

 bodies, but which has greater or less rapidity or inten- 

 sity according to the temperature of those bodies, and 

 if a body which is warmer than those which surround it 

 is cooled on being exposed to their influence, not because 

 it has transferred to them something material, to which 

 the name of caloric has been given, but because of the 

 effect of the action upon it of those bodies by means of 

 their frigorific rays, that is to say, by the undulations 

 caused in the surrounding mass of the fluid ether, un- 

 der these circumstances it is evident that the nature of 

 the exterior surface of the warm body, which renders 

 it more or less capable of reflecting the rays or undula- 

 tions which reach it from surrounding objects colder 

 than itself, ought to influence to a considerable extent 

 the rapidity of the cooling process. 



Now, we know that, of all the substances with which 

 we are acquainted, the metals are the most impervious 

 to light, and, at the same time, and perhaps as a neces- 

 sary consequence, have for it the greatest reflecting 

 power ; moreover, the results of a large number of 

 experiments have shown that they also possess in an 



