Dr. J. Croll on the Transformation of Gravity. '24,1 



But it is not in reference to gravity alone that this space 

 condition is essential to the transformation of potential into 

 kinetic energy. It is, as we shall shortly see, a condition abso- 

 lutely necessary to the transformation of energy under every 

 possible form. In the unbending of a spring the amount of 

 work which can be performed is proportionate to the pressure 

 of the spring multiplied by the space through which the pres- 

 sure can act. The potential element, which in this case de- 

 creases as work is performed, is the tension or elastic force of 

 the spring. Space is necessary simply to allow this tension 

 to expend itself in work. It is this tension, not space, which 

 reappears as work or kinetic energy. Take also the case of 

 the steam-engine. The amount of work which can be per- 

 formed is proportionate to the pressure of the steam in the 

 piston multiplied by the space through which the piston can 

 act. When the piston reaches the end of the cylinder, no 

 more work or transformation of potential energy into kinetic 

 is possible, not because there is no more pressure or potential 

 energy to be transformed, but because there is no more space 

 to allow of transformation. But in order to secure an inex- 

 haustible supply of the sj)ace condition the ingenious device 

 of " reversing the stroke " has been adopted — that is, of trans- 

 ferring the pressure to the opposite side of the piston when it 

 reaches the end of the cylinder. By this device as much 

 space becomes available as would be were the cylinder made 

 a thousand miles in length. In fact the space condition be- 

 comes thus illimitable. But, be it observed, although the work 

 performed is proportionate to the pressure of the steam mul- 

 tiplied by the space through which the pressure acts, still it 

 is the pressure, and the pressure alone, which perforins the 

 work. True the pressure in the cylinder may be kept con- 

 stant ; but this can only be done by admitting more steam 

 from the boiler. The energy which performs the work, or, in 

 other words, which becomes transformed into work, is alto- 

 gether derived from the boiler; the reversal of the stroke 

 simply supplies the space condition for transformation. The 

 energy which disappears as work is performed is heat, not 

 space. The work performed represents so much heat lost. 

 The work is the equivalent of the lost heat, not of the space 

 passed over. "Whatever we have gained in work we have lost 

 in heat. 



Every physicist will readily admit this conclusion in re- 

 ference to an engine propelled by heat, because to suppose 

 that that could perform mechanical work without sustaining 

 loss would in fact be a violation of the principle of conserva- 

 tion. But gravitation turns our water-wheels and grinds our 



