PHYSICAL THEORIES OF HEAT. 587 



as the results of Vibratory Motion*, in 1834 and 

 1 835 ; 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 con- 

 sist of solid molecules, 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 pheno- 

 mena of conduction explained ; for if the molecules 

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

 of vibration, while the others are at rest, the vibra- 

 ting molecules propagate vibrations in the ether, 

 but these 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 molecules, it is only by the repeated im- 

 pulses 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 neces- 

 sarily," M. Ampere adds, " the same equations as 

 those found by Fourier for the distribution of heat, 

 setting out from the same hypothesis, that the tem- 

 perature or heat transmitted is proportional to the 

 difference of the temperatures." 



Since the undulatory hypothesis of heat can thus 



3 Bibliotheque Universelle de Geneve, vol. xlix. p. 225. Ann. 

 Chim. torn. Ivii. p. 434. 



