PHYSICAL THEORIES OF HEAT. 1S3 



verso vibrations ; for no wise pliilosopher would attempt ai, explanation 

 by ascribing poles to the emitted particles, after the experience winch 

 Optics affords, of the utter failure of such machinery. 



But here the question occurs, If heat consists in vibrations, whence 

 arises the extraordinary identity of the laws of its propagation with the 

 laws of the flow of matter ? How is it that, in conducted heat, this 

 vibration creeps slowly from one part of the body to another, the part 

 first heated remaining hottest ; instead of leaving its first place and 

 travelling rapidly to another, as the vibrations of sound and light do I 

 The answer to these questions has been put in a very distinct and plan 

 sible form by that distinguished philosopher, M. Ampere, who published 

 a Note on Heat and Light considered as the results of Vibratory 

 Motion* in 1834 and 1835 ; and though this answer is an hypothesis, 

 it at least shows that there is no fatal force in the difficulty. 



M. Ampere's hypothesis is this ; that bodies consist of solid mole- 

 cules, which may be considered as arranged at intervals in a very rare 

 ether ; and that the vibrations of the molecules, causing vibrations of 

 the ether and caused by them, constitute heat. On these suppositions, 

 we should have the phenomena of conduction explained ; for if the 

 molecules at one end of a bar be hot, and therefore in a state of vibra- 

 tion, while the others are at rest, the vibrating molecules propagate 

 vibrations in the ether, but these vibrations do not produce heat, 

 except in proportion as they put the quiescent molecules of the bar 

 in vibration ; and the ether being very rare compared with the mole- 

 cules, it is only by the repeated impulses of many successive vibrations 

 that the nearest quiescent molecules are made to vibrate ; after which 

 they combine in communicating the vibration to the more remote 

 molecules. " We then find necessarily," M. Ampere adds, " the same 

 equations as those found by Fourier for the distribution of heat, setting 

 out from the same hypothesis, that the temperature or heat transmitted 

 is proportional to the difference of the temperatures. " 



Since the undulatory hypothesis of heat can thus answer all obvious 

 objections, we may consider it as upon its trial, to be confirmed or 

 modified by future discoveries ; and especially by an enlarged know- 

 ledge of the laws of the polarization of heat. 



[2nd Ed.] [Since the first edition was written, the analogies between 

 light and heat have been further extended, as I have already stated. It 



8 Bibliotheque Univei'selle de Geneve, vol. xlix p. 225. Ann. Chim. torn. Ivii 

 p. 434. 



