between Metallic Masses having different Temperatures. 459 



want of connexion of the order of the metals as vibrators with 

 their thermo-electric properties (and especially the absolute inert- 

 ness of antimony and bismuth), convinced me, after a long series 

 of experiments, undertaken with this view, that I was wrong. 



61. The strict and simple connexion with the conducting 

 powers of the metals for heat and electricity, afforded a firm basis 

 for speculation, and I was soon forced to consider heat as the sole 

 agent in the case, all idea of electricity being necessarily aban- 

 doned, as soon as it was established that ^erwo-electricity had no 

 share in the action. The general laws above quoted seem to be 

 all resolvable into this, " that there is a repulsive action exercised 

 in the transmission of heat from one body into another, which has 

 a less power of conducting it." These repulsions only take place 

 between bodies having a certain amount of conducting power, 

 below which some metals fall ; it must be excitable in a most 

 minute space of time ; and is energetic in proportion to the dif- 

 ference of conducting power of the substances, and to their diffe- 

 rence of temperature. 



62. It seems most probable, therefore, that the repulsive action 

 alluded to, depends on the internal motions of heat itself. It were 

 easy to frame a hypothesis which would be sufficiently plausible, 

 and represent the phenomena. I forbear, however, from doing it 

 at present, because our ignorance of the internal constitution of 

 bodies, and the mechanical process of the conduction of bodies, is 

 such as to render hypothetical reasoning upon such data almost 

 useless. That repulsion does exist in the case of heat, can hardly 

 admit of a doubt. The reason that we cannot render it visible 

 in ordinary cases, is no doubt that the repulsion of the heat in 

 two approximate molecules of bodies is too small to be weighed 

 in our balances. Consequently, two bodies equally heated and 

 placed together, manifest no sensible repulsion. In such a case 

 every portion of heat is kept in equilibrium by the equal and op- 

 posite repulsions of the molecules on each side of it, which is the 



VOL. XII. PART II. 3 N 



