450 Mr. J. Croll on certain Hypothetical Elements 



that this definition contains something more than a mere state- 

 ment of the facts determined by observation. It contains a hy- 

 pothetical explanation of the facts. 



Let A and B be two particles of matter. We know experi- 

 mentally that they tend towards each other with a force inversely 

 as the square of their mutual distance ; but the ordinary defini- 

 tion of gravity goes further than this. It not only asserts that 

 they tend towards each other, but it asserts that this force or 

 tendency arises from A attracting B, and B attracting A. It 

 asserts that B moves towards A because B is attracted by it. 



It was demonstrated by Newton, and has been proved by 

 general observation and experience, that bodies tend towards 

 each other with a force varying inversely as the square of the 

 distance, and directly as the mass of the bodies. But it never 

 w T as demonstrated or proved by any one that the bodies attract 

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

 tends towards 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 " attraction " 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 

 towards B. It is not necessary that we should go beyond this, 

 and attempt to explain the cause of this tendency. 



Trifling as this assumption, included in the theory, may at 

 first sight appear to be, it will be found that almost all the diffi- 

 culties 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 towards each other does not 

 imply any 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 Bnicke 

 remarks, " includes that of an action at a distance." 



No principle will ever be generally received that stands in op- 

 position 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 cannot act before it is, or when it is 

 not "*. It probably was with the view of reconciling this hy- 



* For an account of the metaphysical origin of these adages, see a work 

 by the author, 'Philosophy of Theism/ p. 112. Walford, Jackson, and 

 Hodder, Londou, 1857. 



