262 KINETIC THEORIES OF GRAVITATION. 



bodies tend toward each other with a force varying inversely as the 

 square of the distance, and directly as the mass of the bodies. But it 

 never was demonstrated or proved by any one that the bodies attract 

 each other. The thing which has been demonstrated is that B tends 

 toward A ; but the theory does not rest here ; it goes on to account for 

 this tendency by referring it to a hypothetical cause, viz, to the ' attrac- 

 tion ' of A. This however is a mere hypothesis, and no way essential 

 to the theory. All that the theory requires is that it be demonstrated 

 that A tends to move toward B. It is not necessary that we should go 

 beyond this, aud attempt to explain the cause of this tendency. Trifling 

 as this assumption included in the theory may at first sight appear, it 

 will be found that almost all the difficulties and objections which have 

 been urged against the theory of gravitation are due in some form or 

 other to that assumption. At the very outset we have the objection 

 urged against the theory that it implies the absurdity of action at a 

 distance. Now the mere facts of gravitation imply no such thing. 

 That A and B placed at a distance should tend toward each other does 

 not imply action at a distance. A moves by virtue of a force, but it 

 does not follow that this force is at a distance from A. But if we assert 

 that A and B 'attract' each other, then we imply action at a distance; 

 for A is then affirmed to move in consequence of the force of B, and B 

 in consequence of the force of A. ' The very idea of attractive force,' 

 as Professor Briicke remarks, ' includes that of an action at a distance.' 

 No principle will ever be generally received that stands in opposition 

 to the old adage, 'A thing cannot act where it is not,' any more than it 

 would were it to stand in opposition to that other adage, 'A thing can- 

 not act before it is, or when it is not.' " * 



These venerable " adages " are about as valuable in directing us to 

 the actual facts of nature, as that other celebrated adage of Zeno, " a 

 body cannot move where it is not;" and conversely, "it cannot move 

 where it is." An equally profound dictum is, that a " cause " cannot 

 properly be said to precede its " effect," since succession implies discon- 

 tinuity. 



It may be a fact of natural law that everything "acts where it is not," 

 including even an aetherial vibration ; and certainly there is no difficulty 

 in believing it ; aud the other metaphysical axiom may be easily dis- 

 credited by the simple reflection, that were our sun suddenly blotted 

 from existence by supreme power, though all " attraction" of the planets 

 would instantly cease, its full dynamic action on the earth would con- 

 tinue unimpaired for eight minutes. Were Sirius annihilated this year, 

 it would still continue to pour upon us its lull measure of dynamic ac- 

 tion for twenty years " when it was not." The difficulty is not in the 

 possibility of posthumous action, but in the possibility of annihilation. 



As TNI ill lias very properly stated in answer to Sir William Hamilton, 

 "Action at a distance is intrinsically quite as credible as action in con- 



* L. E. D. Phil. Mag., December, 1867, vol. sxsiv, p. 450. 



