﻿Principles of Molecular Physics. 283 



say only that with the scanty knowledge we have of the bodies 

 that move in heavenly spaces, and after the discovery of so many 

 new planets, the existence of which had never been suspected 

 before, it would be too rash on the part of a man of science to 

 pronounce that no other cause exists in the heavens to which we 

 can trace the change of Encke's comet course, except a resisting 

 medium. The more so, since Encke's comet shows a regular acce- 

 leration of its motion, instead of a retardation. Now acceleration 

 does not proclaim, but refute, the theory of a resisting medium ; 

 and therefore Encke's comet and all the other celestial bodies with 

 one loud voice proclaim, and witness in fact, the absolute non- 

 existence of a resisting medium " (Molecular Mechanics, pp. 1 78, 

 179). 



Professor Norton goes on arguing : 



" The fact that no sensible resistance is experienced by the pla- 

 nets does not necessarily imply, as he supposes, that the aether is not 

 repulsive. For, in the first place, if the molecules of the planetary 

 mass have the constitution I have attributed to them, the impinging 

 sether must take effect upon either the sethereal or the electric atmo- 

 spheres of the molecules, and so may be mostly expended in the ge- 

 neration of heat and electric currents. I have in fact undertaken to 

 show, in my paper on Molecular Physics, that the earth may derive 

 its magnetic condition and a certain portion of its heat from the 

 impact of the sether of space." 



In this argument the learned Professor assumes (1) that the 

 molecules of the planetary masses have the constitution which he 

 has attributed to them, and (2) that the impinging sether spends 

 the greatest part of its impetus in producing heat and electric 

 currents. The first of these assumptions has been examined 

 sufficiently, I believe, in the preceding pages. With regard to 

 the second (which apparently would not stand without the first) 

 I may add that, in my opinion, no possible production of heat 

 and electric currents affords a sufficient ground for assuming a 

 reduction of resistance and retardation. Impact is a mechanical 

 fact, the first, direct, immediate result of which is not a produc- 

 tion of heat or of electric currents, but simply a communication 

 of motion in a certain direction. Accordingly the impact of 

 aether on a planet primarily and directly tends to check its velo- 

 city of translation through space : and only inasmuch as the 

 effect of this effort cannot instantaneously be transmitted from 

 the surface of the planet, where it is exerted, to the remaining 

 molecules of the planetary mass, it gives rise to intermolecular 

 motion. In other words, the generation of heat or of electric 

 currents depends upon the actual diminution of the velocity of 

 translation as a previous condition, intermolecular motion being 

 the result of a preceding change in the mutual relation of mole- 



