KINETIC THEORIES OF Gr.AVITATION. 249 



ing forces is daily exliibited to us in the behavior of the magnet. 

 Another possible conception is that repulsion is a positive material or 

 cetlierial atmosphere of definite radius. 



Indeed, the author's theory is really one of the superposition of two 

 systems of waves, rather than one of a single system changing its sign. 

 For he supposes that the attraction of gravity results from cetherial 

 waves of great longtli and correspondingly large excursions or ampli- 

 tudes, in which the diameter of the material atom is a vanishing quan- 

 tity ("//=0"), and there is no sensible dilference between the velocities 

 on its two hemispheres; while atomic repulsion results from such 

 small waves (smaller even than those of light) that the atom is large in 

 comparison, and the difference of the wave on its two hemispheres is 

 very notable. " Thus the conditions assumed in the mathematical the- 

 ory of heat are satisfied by supposing // to be very large and q [the ex- 

 cursion of the wave] to be very sm«ll ; and the fulfillment of these con- 

 ditions accounts for the great energy of calorific repulsion. . . Hence 

 atoms of very small size, acting upon each other by the intervention of 

 waves of which the excursions are very small, mutually repel with a 

 very great force ; and at the same time, as was shown in the Theory 

 of Ileat, the force varies very rai)idly with the distance." 



Attributing to the spherical hard atom of matter only ineitia, "it 

 would be contrary to these piinciples to ascribe to an aton> the property 

 of elasticity, because from what we know of this property by experience 

 it is quantitative, and being most probably dependent on an aggrega- 

 tion of atoms, may admit of explanation by a complete theory of mole- 

 cular forces." * Of this fundamental property however, — necessarily 

 precedent to idl theory of wave action, — no explanation is given. 



That the author did not feel entirely satisfied with his vibiatory theory 

 of molecular forces, would a])pear fiom his returning to the subject two 

 years later with the remark : " Such vibrations, when we calculate their 

 effect only to the first power of the velocity, are found to produce simply 

 oscillations of small spherical bodies submitted to their action, and not 

 motion of translation. To account for the latter, it is necessary to pro- 

 ceed to the consideration of eflects due to the second power of the ve- 

 locity Lastly, there is yet another physical force, the 



relations of which to an cetherial medium and to other modes of force 

 are not readily made out : I mean the Ibrce of gravity. If however, all 

 the other forces are modifications of aitherial pressure, it is reasonable to 

 suppose that this one is of the same kind. I have ventured to reason 

 on this supposition, and have attempted to deduce (I think with success) 

 the known laws of gravity from the dynamical action of tetherial waves 

 of much larger magnitude than those which correspond to molecular 

 forces." t 



While it is comparatively easy to explain the origin of heat-waves 



* L. E. D. Phil. Mag., February, 1800, vol. six, pp. 89-91. 

 tL. E. D. Phil. Mag., April, 18G2, vol. xxiii, pp. .319, 320. 



