KINETIC THEORIES OF GRAVITATION. 253 



(ion or verification, " The whole theory however of attractive and re- 

 pulsive forces, regarded as due to vibrations of the aether, is incomplete 

 for want of an a priori determination of the composition and value of 

 the quantity II."* 



In 187G, the author returns to the discussion with a view "to correct 

 in certain respects that investigation, [the one last cited,] and to carry it 

 a step further." And in dealing with a residual effect of vibration, 

 " which in fact is the attraction of gravity? and determining that the 

 accelerative force is independent of the size of the atom or molecule, 

 he says: "This result expresses the force of gravity as due to the at- 

 tractive action of a molecule of a higher order as to magnitude than the 

 molecule of molecular attraction. For distinction, a molecule of this 

 superior order might be called a gravity-molecule. Its magnitude may 

 still be considered to be so small that in comparison with the magni- 

 tudes of »<jrrestrial and cosmical masses, it may be treated as an infini- 

 tesimal quantity Lastly, it is to be noticed that on account of 



the large value of A for gravity- waves, they do not suffer sensible retarda- 

 tion or refraction in passing through gross bodies. I have ou several 

 previous occasions, tieated of the problem of gravitating force theoreti- 

 cally, and by slow steps have approximated to its solution ; but before 

 the present attempt, I had not succeeded in exhibiting satisfactorily the 

 rationale of this kind of attraction by vibrations,'' t 



Such is an imperfect abstract of the most carefully-studied and the 

 most diligently-elaborated exposition of the wave-theory of attraction 

 which has yet been proffered to the scientific world. Discussed with 

 the earnestness and candor of a fervent conviction, and with all the 

 resources of a high order of mathematical culture and ability, the re- 

 sult yet fails, sadly and fatally, to satisfy the conditions of the problem. 

 Strong as is the author's assurance that he has successfully grasped by 

 his formulas and equations the several functions embraced in the first 

 three of our propositions,^: this is by no means mathematically estab- 

 lished; and the last three propositions are hopelessly ignored and vio- 

 lated. We have st-eu that Elasticity, that puzzling u occult quality," 

 driven out from the sober presence of the purely rational atom, has in an 

 inexplicable manner, slipped in by the back-door of oetherial pressure. 



Naturam expvllts furca, tamen usque recurret, 

 FA mala ptrrumpet furtim faslidia vietrix. 



With the multitudinous duties imposed upon the much-suffering 

 aether, in all the varying ranges and orders of undulations derived from 

 atoms and from molecules with ever-changiug motions, amid all the 

 perturbations and transformations of the mechanical energy of matter, 



* L. E. D. Phil. Mug., September. 1872; vol. xliv, pp. 203,204, 209. 



+ Phil. Mag., September, 1876, vol. ii, p. 191. 



i Principles of Mathematics ami Physics, p. 499. In the concluding chapter of the 

 work, the author diaws strength aud encouragement from a quotation of the celebrated 

 '• Third Letter to Beutley.'' 



