the Structure of (lie Earth. 



ceive attraction and repulsion of the very same particles exert- 

 ing reciprocal influence at one and the same time. 



For this, among other reasons, it is not unsatisfactory to 

 consider heat as a substantial cause of repulsion between par- 

 ticles which are endued with a mutually attractive power. 



Exhibition of heat is attended with dilatation of bodies, as 

 abstraction of it is with contraction. The integrant particles are 

 approximated in one case, and rendered more distant in the 

 other. The cause of increased remoteness is a repellent one ; 

 none merely divellent being implied. It may be conceived as a 

 material substance, equally diffused throughout infinite space, 

 or tending to uniform dissemination, whenever that equality is 

 by any cause locally disturbed. 



In such a state of equilibrium, a fluid purely repulsive, as 

 heat is here supposed to be, would be an unresisting medium, 

 offering no opposition to the inertness of matter. Equally dif- 

 fused and perfectly balanced, it presents no resistance to mo- 

 tion nor opposition to rest. For such repulsion, exercised on all 

 sides alike, cannot disturb repose ; nor can it impede progres- 

 sion of a body, or of a mass of matter moving consentaneously ; 

 since the fluid, alike repulsive in all directions, impels the mov- 

 ing body in accordance with its motion, precisely as much as it 

 conversely opposes it on the other part. But it may resist the 

 coarctation of matter, between portions of which it is inter- 

 posed: because the approach of matter moving contrariwise 

 cannot take effect, without disturbing the equal diffusion of the 

 repulsive fluid, by pressure of portions which are by that ap- 

 proach displaced. 



It is only in maintenance or retrieval of such uniform diffu- 

 sion, that heat exerts an influence upon the particles of gravi- 

 tating matter disseminated in it, or between which it is inter- 

 posed ; and affects the position and relative distances of those 

 particles by an energy contrary to their mutual attractive power. 

 By those conflicting forces, a substance is made to pass through 

 all the stages from the solid to the gaseous state. 



Heat has been conceived as pushing apart the minute por- 

 tions of matter, between which it penetrates in seeking its own 

 umform difHision ; and as insinuating itBclf for the same end 



