KINETIC THEORIES OF GRAVITATION. 249 



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

 Auother possible conception is that repulsion is a positive material or 

 setherial atmosphere of definite radius. 



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

 systems of waves, rather thau one of a single system changing its sigu. 

 For he supposes that the attraction of gravity results from aetherial 

 waves of great length and correspondingly large excursions or ampli- 

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

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

 on its two hemispheres; while atomic repulsion resu'ts 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 /z to be very large and q [the ex- 

 cursion of the wave] to be very small ; 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 Heat, the force varies very rapidly with the distance." 



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

 would be contrary to these principles to ascribe to an atom 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 all theory of wave action, — no explanation is given. 



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

 of molecular forces, would appear from 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 effects due to the second power of the ve- 

 locity Lastly, there is yet another physical force, the 



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

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

 the other forces are modifications of aetherial 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 retherial waves 

 of much larger magnitude thau those which correspond to molecular 

 forces." t 



While it is comparatively easy to explain the origin of heatwaves 



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

 tL. E. D. Phil. Mag., April, 1862, vol. xxiii. pp. 319, 320. 



