of the principal Ph(snomena of Heat, 347 



son a particle of heat attempting to escape from the surface of 

 a metallic body is more strongly drawn back by the attractive 

 force of the particles than at the surface of other bodies. 

 The metals have therefore less radiating power than any other 

 substances. 



11. The particles of heat emerging from the surfaces of solid 

 bodies at angles so small as to be drawn back again into their 

 substance, form collectively an atmosphere enveloping those 

 surfaces, and extending, there is reason to believe, to distances 

 considerably greater than the interval which separates the 

 solid particles from one another. It is to this atmosphere 

 that we must attribute the repulsive power exerted at the sur- 

 faces of bodies, metallic bodies especially, by virtue of which 

 mercury is depressed in a barometer tub^, and a steel needle 

 floats on the surface of water. By strong pressure this en- 

 veloping atmosphere may be expelled from between two me- 

 tallic surfaces, and the attractive force of their particles then 

 coming into play, they adhere with considerable force. The 

 reflexion of heat at the surfaces of bodies also appears to be 

 due to the action of this enveloping atmosphere. 



12. It may facilitate the apprehension of my meaning to 

 observe, that a particle of matter, with its revolving particles of 

 heat, is supposed to have a resemblance to the sun, with its 

 accompanying bodies, in the solar system. The planets, re- 

 volving in elliptic orbits, represent the particles of latent heat ; 

 the comets, if indeed any of them revolve, as formerly sup- 

 posed, in parabolic or hyperbolic orbits, represent the par- 

 ticles of sensible heat. Future observations will, perhaps, en- 

 able us to determine the law of the forces by which these minute 

 movements are regulated, as accurately as we are now ac- 

 quainted with the law of gravitation. The preceding conclu- 

 sions are, however, independent of the particular law of those 

 forces. 



January 27, 1837- 



P.S. I have assumed, in conformity with the views of La- 

 place and other mathematicians, that the particles of solid 

 matter mutually attract each other. But the preceding con- 

 clusions hold good though no such force of attraction exists, 

 or even if we suppose with iEpinus that the particles mu- 

 tually repel each other, a supposition which is by no means 

 incompatible, as Dr. Roget has observed*, with the phaeno- 

 mena of gravitation. There are certainly strong reasons in 

 support of this last hypothesis. 



* See SciENTinc Memoibs, Part III. p. 469.— Edit. 

 2 Y2 



