274 KINETIC THEORIES OF GRAVITATION. 



In this resume of kinetic theories, doubtless other names, well de- 

 serving notice, have been overlooked from want of more extended re- 

 search 5 but it is believed that the foregoing survey comprises essentially 

 all the forms of the hypothesis of primeval motion which have been 

 propounded. The general tenor of this line of speculation has been 

 well set forth in an able review of " The Atomic Theory of Lucretius," 

 which appeared in the North British Eeview for 1868. 



'.'The most plausible suggestion yet made by this school is that a 

 single omnipresent fluid aether fills the univ^ersej that by various 

 motions of the nature of eddies, the qualities of cohesion, elasticity, 

 hardness, weight, masS) or other universal properties of matter are 

 given to small portions of the fluid which constitute the chemical 

 atoms; that these, by modifications in their combination, form, and 

 motion, produce all the accidental phenomena of gross matter ; that 

 the primary fluid by other motions, transmits light, radiant heat, mag- 

 netism, and gravitation; that in certain ways, the portions of the fluid 

 transmuted into gross matter can be acted upon by the primary fluid 

 which remains imponderable or very light, but that these ways differ 

 very much from those in which one part of gross matter acts upon 

 another ; that the transmutation of the primary fluid into gross matter, 

 or of gross matter into primary fluid, is a creative action wholly denied 

 to us; the sum of each remaining constant."* The hypothesis of the 

 transmutation of SBther, or of the evolution of " matter," is not how- 

 ever necessarily involved in that of referring all conditions, properties, 

 and powers of matter to "a mode of motion." 



General Conclusions. 



In the conception of a statical pressure of aether constantly acting 

 inwardly on concentric spherical surfaces, there is the obvious irration- 

 ality of a stable non-equilibrium. Nor is there any real difference in 

 the conception of an aether having concentric increments of density 

 outward, in which ordinary matter is buoyed, as it were, toward the 

 center: a scheme in which every particle of matter finds itself in the 

 midst of its own little spheres of rarefaction, and in which such center 

 of aetherial rarity is supposed to blindly follow the flying stone in what- 

 ever direction hurled at the caprice of an idle boy. Entirely too much 

 importance has beoi attached to this conception as a speculation of 

 Newton, when it was evidently an unconsidered and merely obiter dictum 

 suggestion, utterly repudiated by him in later years. 



Omitting then any further consideration of the statical method of 

 explaining gravitation by pressure, we find that Icinetic systems are 

 essentially of two classes, the hypotheses of emissions or corpuscles, 

 and the hypotheses of fluid undulations. It is proposed to show that 

 no form of either hypothesis can satisfy the two Newtonian conditions 

 of a scientific theory — verity and sufficiency. 



"North British Review, March, 18GS, vol. xlviii, p. 127 of Am. edition. 



