258 ON l^li NATi.«^RE OF HEAT. 



and Euler their ethereal medium ; althouj^h both supposi- 

 tions are equally hypothetical. 

 Neglect of in- It fnust be acknowledged, that in investigating the nature 

 ductien of caloric, we subject ourselves to the imputation of false 



philosophy. We neglect the method of induction, and seek, 

 as the ancients did, occult causes. So much are we involved 

 in the trammels of theory, that we are scarcely able, in some 

 and recourse u> ^'^'^^^^^^s* ^^ express a single fact, without implying the ex- 

 hypoihcsis too istence of something perfectly hypothetical ; this is very 

 much the case with our present subject, heat, and with the 

 science of electricity. AVe are educated in the belief of such 

 hypotheses, and do not doubt of their truth, until a consider- 

 able progress has been made in the study of them. It ig 

 not one of the least of the uses of investigations like the 

 present, to teach us how very little all hypotheses ought to 

 be relied on, and how very much and how constantly they 

 ought to be distrusted. 



The Nature of the Vibration of Heat, 



Kature of the Heat may possibly depend, not on the presence of any 

 Vibration of material fluid in the interstices of bodies, but on a state of 

 intimate vibration of their particles. The temperature or 

 ' degree of heat may be greater or less, according as these 



vibrations may be more or less frequent in any given time; 

 or, as it may be expressed, according to the intensity of the 

 vibration. By this term I wish only to express the relative 

 state of the vibration; that vibration I suppose to be the 

 most intense, which occasions the highest temperature. 

 Objection to ^" objection which has always been urged to the hypo- 

 the hypothesis, thesis of vibration is, that the propagation of heat does not 

 obey the established laws of motion. '* Were they the same, 

 its propagation ought to be momentary through elastic bo- 

 dies, and should be more or less rapid through others, ac- 

 cording to their elasticity." 



Answer to the '^^ *^^ ^""^^ P^*"^ ^^ ^^'^ objection, it may be answered, 

 first part of it. that the propagation of heat through elastic bodies is indeed 

 momentary ; for this is the radiation of caloric. Previously^ 

 to considering the second part of the objection, it will be] 

 necessary to consider somewhat of the nature of the vibra- 

 tions, 



