252 Dr. J. CroU on the Transformation of Gravity. 



as the equivalent of the motion gained, is simply the distance 

 between the stone and the ground. Consequently space is 

 not only made a part of the potential energy, but the only 

 part out of which the kinetic energy has been generated — 

 space or distance from the ground being the form in which 

 the energy of the falling stone previously existed. 



Gravity a Space-pervading Force. — The fact that gravity 

 increases inversely as the square of the distance may be re- 

 garded as evidence of the truth of the views advocated by Fara- 

 day*, Waterstont, and others, that it is a force pervading 

 space external to bodies, and that on the mutual approach of the 

 bodies this force is not increased as is generally supposed, but 

 the bodies merely pass into a place where the force exists with 

 greater intensity ; for in such a case the intensity of the 

 force, in the space external to any body, is inversely as the 

 square of the distance from the centre of convergence of these 

 lines of force. When a stone, projected upwards, recedes from 

 the earth, its vis viva is transferred to space, and exists there 

 as gravity. When the stone approaches the earth, the force 

 existing in space is transferred back to the body and reappears 

 as vis viva. 



"The integral of gravitation," says Mr. Waterston, "is a 

 function of space. . . . Each element of radial distance has 

 associated with it a fixed element of mechanical force, to be 

 given or taken from all bodies traversing it." 



Gravity supposed to be an Impact or a Pressure. — It is now 

 generally admitted that the conception of attraction does not 

 represent the modus operandi of gravitation, because attrac- 

 tion implies action at a distance, or, in other words, that a 

 thing acts where it is not, which is just as impossible as that 

 a thing can act when it is not. Gravity, in all probability, is 

 of the nature of an impact or a pressure. Some of our most 

 eminent physicists state that the force of gravity must either 

 result from impact of ultramundane corpuscles, in some respects 

 analogous to that of the particles of a gas (which has been 

 found to be capable of accounting for gaseous pressure), or it 

 must result from difference of pressure in a substance con- 

 tinuously filling space, except where matter displaces it. 



That gravity is a force of the nature of pressure is, I think, 

 beyond all doubt ; but that this pressure results from the im- 

 pact of corpuscles or from difference of pressure in a substance 

 filling space is purely hypothetical. Why not assume it to 



* Phil. Mag. April 1857 : Proceedings of the Eoyal Institution for 

 1855. 



t Phil. Mag. [IV.] vol. xv. 



