234 KINETIC THEORIES OF GRAVITATION. 



annihilated in regard to A, and the force in A will be annihilated at 

 the same time."* Although it is certainly true that when B is removed 

 to an infinite distance from A, the power of A upon B will be infinitely 

 diminished, it is not a sound inference that "the power in A will be 

 infinitely diminished." The same inaccuracy occurs in the assumption 

 that if an isolated particle " could not gravitate" it could have " no force 

 of gravity." This is but another expression of the not unusual sophism 

 that force has no existence unless in active exercise. 



Varying his illustration to attack the problem of mass, Professor 

 Faraday thus further unfolds his difficulties: "The particle A will 

 attract the particle B at the distance of a mile with a certain degree of 

 force ; it will attract the particle C at the same distance of a mile, with 

 a power equal to that by which it attracts B. If myriads of like par- 

 ticles be placed at the given distance of a mile, A will attract each with 

 equal force. . . . How are we to conceive of this force growing up 

 in A to a million-fold or more ? And if the surrounding particles be 

 then removed, of its diminution in an equal degree? Or how are we 

 to look upon the power raised up in all these outer x^articles by the 

 action of A on them, or by their action one on another, without admit- 

 ting (according to the limited definition of gravitation) the facile genera- 

 tion and annihilation of force ?" The substance of this enigma is com- 

 prised in the corollary to our second proposition. Striking out the 

 fallacious expression "of this force growing up in A," which has already 

 beeu sufficiently criticised, surely the case as stated, is a very good 

 illustration of " conservation." The hypothetical generation and anni- 

 hilation of the distant particles surrounding A are just as "facile" as 

 the hypothetical " generation and annihilation of force " exercised by 

 them; but no whit more so. As if one should say, imagine the clock 

 wound up, and it will run a week. The equation is correct only on con- 

 dition that both the terms are equally real or equally imaginary. 



Inasmuch as the accepted definition of gravitative force (deemed by 

 Faraday so objejctionable) is merely the summation of an over^'helming 

 induction derived from a ceaseless observation, the question naturally 

 arises, to what point are the difficulties imagined by him supposed to 

 tend ? " The principle of the conservation of force would lead us to 

 assume that when A and B attract each other less because of increas- 

 ing distance, then some other exertion of power, either within or with- 

 out them, is proportionately growing up. And again that when their 

 distance is diminished, as from 10 to 1, the power of attraction, now in- 

 creased a hundred-fold, has been produced out of some other form of 

 power which has been equivalently reduced."! Were gravity merely a 

 dynamic energy, generated in time and space by an anterior and exte- 

 rior force, the inference would undoubtedly be correct. Conversely, the 

 utter falsity of the inference, as established by all experience, in which 



* L. E. D. Phil. Mag. 1857, vol. xiii, pp. 228, 2^9. 

 t £oco ci/a^., pp. 230, 231. 



