456 Mr. J. Croll on certain Hypothetical Elements 



It is, of course, perfectly true, as has been stated, that the work 

 performed by gravity is in proportion to the pull of gravitation 

 x the distance through which the pull can act. And the work 

 performed by the piston is in proportion to the pressure of the 

 steam x the length of stroke. But then, if space be nothing 

 more than a condition in the operation, the energy must be 

 derived from the pressure, not from the space. The gain of 

 energy, or the work, would be in this case exactly equal to the 

 loss of pressure or force, the space being simply the condition 

 which allows the change from force to energy to take place. 



Time and space are necessary conditions in all phenomena, 

 whether of mind or matter, but they are mere conditions. We 

 believe, in opposition to Kant, in the objective reality of time 

 and space ; but still, though space is an objective reality, a thing 

 in itself, it can no more be converted into a force or an energy 

 than it can be converted into a stone. The one supposition 

 appears just as extravagant and absurd as the other. It is just 

 as violent an assumption to suppose that time could be con- 

 verted into energy, become an efficient cause in the performance 

 of work, as that space could be so converted. Space has been 

 eternally space, and can absolutely be nothing else. 



But supposing that space could be something more than a 

 mere condition in the transference of the force of gravitation 

 into mechanical energy, still this would not reconcile the ordi- 

 nary theory with the principle of conservation. 



In the case of the loaded piston rising under the pressure of 

 the steam, we have the pressure of the steam and length of 

 space both diminishing as the vis viva or mechanical work in- 

 creases. This is in. harmony with the principle of conserva- 

 tion, for pressure or force diminishes as energy or work in- 

 creases. But in the case of gravitation matters are reversed; 

 for the force increases along with the work. As the weight 

 descends and performs work, the pressure of the weight, the 

 thing which performs the work, increases also. And when the 

 weight is rising and energy diminishing, the force or pressure 

 of the weight is not increasing but actually diminishing also. 



This difficulty, along with all the others which we have been 

 considering, will entirely vanish if we adopt the view of gravity 

 which has been ably advocated by Faraday*, Waterstonf, and 

 other physicists, viz. that it is a force pervading space external 

 o bodies, and that on their mutual approach this force is not 

 increased as is generally supposed, the bodies merely pass into 

 a place where the force exists with greater intensity ; for in 



* Phil. Mag. April 1857. Proceedings of the Royal Institution for 

 1855. 



t Phil. Mag. S. 4. vol. xv. 



