2 L8 Dr, J. Croll on //«' Transformation of Gracit//. 



corn, performing mechanical work as truly as it is done by heat ; 

 and all tins is supposed to take place without gravitation sus- 

 taining any loss. The only thing supposed to be lost is posi- 

 tion or space to pass over. Gravity is the real agent that 

 performs the work ; and yet it is supposed to sustain no loss 

 thereby. Heat in the steam-engine is the agent that perforins 

 the work ; but it would be considered absurd to say that no 

 heat was lost, and that what was lost was simply space in the 

 cylinder, along which the piston could move. The absurdity 

 seems, however, to be quite as great in the one case as in 

 the other ; and it appears as much a violation of the principle 

 of conservation to suppose that gravitation could perform work 

 without loss as that heat could do so. That form of energy 

 called heat is weakened by the act of raising the loaded piston 

 against gravity. May not that form of energy called gravity 

 be also weakened by the act of pulling the piston down ? 



It is true that the pressure of the steam has a dynamical 

 origin, and that in the performance of work there is a loss of 

 pressure resulting from a loss of molecular motion. May not 

 the same be equally true of gravity ? In fact, if gravity has 

 a dynamical origin, it must hold equally true of gravity and of 

 heat. If the force of gravity, for example, results (as it, how- 

 ever, probably does not) from the impact of ultramundane 

 corpuscles, as advanced by M. Le Sage, then there must be a 

 loss of force resulting from a loss of corpuscular motion when 

 work is performed, as truly as in the case of the steam-engine ; 

 in fact the two cases are exactly parallel. 



That space is not a form of energy but simply a condition, 

 becomes further evident from the nature of kinetic energy in 

 the form of motion. The kinetic energy of a moving body is 

 equal to its mass multiplied by the half-square of its velocity. 

 Now it must be observed that the energy possessed by the 

 body depends upon its velocity, and is entirely independent 

 of the amount of space passed over. A body moving with a 

 certain velocity possesses the same amount of energy what- 

 ever may be the space passed over. A one-pound weight 

 moving at the rate of 1000 feet per second possesses 15,625 

 foot-pounds of energy, whether it moves over one thousandth 

 of a hairbreadth or over one thousand miles. It would not pos- 

 sess any more energy without a change of velocity though it 

 were to continue its course onward in space through all 

 eternity. The energy possessed is the same whether the 

 space passed over be infinitely great or infinitely small, 

 which would not be the case if space were itself a form of 

 energy. 



In order to perceive more clearly the true relationship of 



