246 Dr. J. Croll on the Transformation of Gravity, 



anv height : but if ii can only descend through one foot and no 

 more, one foot-pound of the potential energy stored up in the 

 form of gravity can be transformed into the kinetic form ; but 

 if two feet, three feet, ten feet, fifty feet, and so on be supplied, 

 two foot-pounds, three foot-pounds, ten foot-pounds, and soon 

 of potential energy will be converted into kinetic. The amount 

 of transformation will be in proportion to the amount of the 

 space condition supplied. When the stone reaches the ground 

 no further transformation can take place, not because the 

 potential energy is exhausted, but because no further space 

 condition is available. But were a hole dug through the 

 earth the stone would continue its descent, and transformation 

 would go on till the earth's centre was reached, when the 

 entire amount of potential energy of gravity acting on the 

 stone would have disappeared and no further transformation 

 of potential energy into kinetic would be possible — not, how- 

 ever, as before, because there was no more space condition, 

 but because there would be no more gravitating force acting 

 on the stone. 



It is gravity, and gravity alone, which imparts motion to 

 the stone. No work is performed on the stone by space ; 

 space and time merely supply the conditions for the work 

 being done. That which, in the potential state, becomes trans- 

 formed into kinetic energy must be gravity, not space. The 

 kinetic energy which appears as the stone descends must have 

 previously existed in the form of gravity, not as space. This 

 truth is so self-evident that it can hardly be denied by any 

 one who will reflect on the subject. But if the kinetic energy 

 be derived from gravity, then there must be a decrease of 

 gravity proportionate to the increase of kinetic energy, or 

 else the principle of conservation is violated. If a force be 

 transformed into something else, say into kinetic energy, then 

 it cannot be what it was before transformation, but must be 

 what it is transformed into, viz. kinetic energy*. 



* Mr. Lewes, in his l Problems of Life and Mind ' (vol. ii. p. 358), lays 

 it down as a fundamental principle that force is invariant and cannot be 

 expended or even transformed. Every unit of force, according to him, 

 remains unalterably the same in amount. His views seem to be : — that 

 when the forces balance one another there is rest, static equilibri 



rium 



but when there is an excess of pressure in one direction, motion or vis 

 viva results ; but the forces themselves are invariant, and never increase 

 or diminish. This is just the fundamental error which I have been 

 combating. Force, I consider, is energy in the potential form ; motion is 

 energy in the kinetic form. Neither the one nor the other remains con- 

 stant, but both are in a state of change. That which remains constant 

 is the sum total of* both. And as the one is convertible into the other, it 

 necessarily follows that the one must decrease as the other increases, and 

 pice versa. 



