400 W. A. Norton—Physical Constitution of the Sun, 



led to infer that the repulsive action exerted hy the sun upm mat- 

 ter in the state of the cometary vapors, probably consists, either wholly 

 or partially, in repulsive impulses propagated in the heat waves 

 proceeding from the sun. 



Let us now see whether any confirmation of these inferences, 

 and any additional light in the direction of our present iBquirv. 

 can be obtained on the substantial ground of Ten-estrial Ph\s- 

 ics. The definite question presented for consideration,' is 

 whether the results of observation or experiment afford any 

 indication of a direct repulsive action exerted by radiant heat 

 on the atoms of bodies. It is universally admitted that radiant 

 heat, when imbibed by a body, acts as a repulsive or separating 

 agency among its molecules. It is also conceived that the con- 

 duction of heat is by radiation from atom to atom. The most 

 natural inference from these facts is that the waves of radiant 

 heat, which pass from atom to atom, directly urge the atoms away 

 from each other by repulsive impulses. Instead, however, of 

 adopting this simple idea, physicists have generally been in- 

 clined to refer the expansion of bodies from heat to some 

 mode of motion of the atoms, originated by the heat received; 

 though no detailed satisfactory explanation has yet been given 

 of the manner in which such motions would directly originate 

 an expansion. Strangely enough this notion is even entertained 

 by physicists who regard heat as the only cause of the repulsion 

 subsisting among the molecules of bodies. It should here be 

 noted, that if the expansion of all bodies of matter fi-om heat 

 is to be ascribed to a direct impulsive, or repulsive action of heat 

 waves proceeding from one atom and falling upon the surroinid- 

 ing atoms, then this force takes effect at the greatest distances 

 by which the atoms are separated in the rarest gas under the 

 feeblest pressure; and we would thus be led to expect that 

 heated bodies in contact with each other might manifest signs 

 of repulsion. 



In point of fact, many evidences of a heat repulsion subsist- 

 ing between particles of different bodies, in contact or in close 

 proximity, have been adduced by different experimentalists, 

 and writers on physics, some of which may be briefly men- 

 tioned. 



1. " When pure silica, in an extreme state of division is 

 highly heated, the slightest motion then causes the particles of 

 the powder to slide over each other, and the surface of the 

 powder is thrown into undulations almost like those oi a 

 liquid." 



2. A rise of temperature is attended with a decrease ot 

 capillary attraction. Also the frictional resistance to the flow 

 of water in pipes is diminished by heat. " 



