io6 Inquiry concerning the Nature of Heat y 



bodies, and the slower undulations, occasioned by the 

 vibrations of those colder bodies, will act as frigorific 

 rays on the hot body ; and these reciprocal actions will 

 continue, but with decreasing intensity, till the hot 

 body and those colder bodies which surround it shall, 

 in consequence of these actions, have acquired the same 

 temperature, or until their vibrations have become iso- 

 chronous. 



According to this hypothesis, cold can with no more 

 propriety be considered as the absence of heat than a 

 low or grave sound can be considered as the absence of 

 a higher or more acute note ; and the admission of rays 

 which generate cold involves no absurdity and creates 

 no confusion of ideas. 



On a superficial view of the subject, it may perhaps 

 appear difficult to reconcile solidity, hardness, and elas- 

 ticity with those never-ceasing motions which we have 

 supposed to exist among the constituent particles of all 

 bodies ; but a patient investigation of the 'matter will 

 show that the admission of that supposed fact, instead 

 of rendering it more difficult to form distinct and satis- 

 factory ideas of the causes on which those qualities of 

 bodies depend, will rather facilitate those abstruse re- 

 searches. 



Judging from all the operations of nature, of the causes 

 of which we are able to form any distinct ideas, we are 

 certainly led to conclude that the force of dead matter 

 (and perhaps of living matter also), or its power of 

 affecting, that is to say, of moving other matter, or of 

 resisting its impulse^ depends on its motion. 



If, therefore, solid (or fluid) bodies have any powers 

 whatever, either of impulse or of resistance, it appears 

 to me to be more reasonable to ascribe them to the 



