ON THE ORIGIN OF FORCE. 47I 



tilings there would take place periodically, so to speak, 

 a winding up from a lower to a higher state of potential 

 energy, to be subsequently exchanged for newly-created 

 vis viva. But as we can have no such ct priori assur- 

 ance, can only assume such restoration to be possible, 

 and can see no means of effecting it, if possible, other- 

 wise than by foresight and prearrangement ; the one 

 equally with the other is an unknown function, vari- 

 able within unknown limits, and susceptible of fluc- 

 tuations to an unknown extent, nor can we have any, 

 the smallest, right to assert that what is expended in the 

 one form is, necessarily, laid up in reserve for further use 

 in the other. It would be very diftcult, I apprehend, to 

 show whether in the winding up of a clock, or the build- 

 ing of a pyramid, taking into consideration all the various 

 modes in which vis viva disappears and reappears in the 

 expenditure of muscular power, the evolution of animal 

 heat, the consumption of the materials of our tissues 

 (laying aside all question as to the evolution of force 

 from intellectual effort), the propagation of vibratory 

 motion, and a thousand other modes of transfer; the total 

 vis viva of this our planet is increased or diminished. 

 That it should remain absolutely unchanged during the 

 process is in the last degree inconceivable. The amount 

 of 7!is viva latent in the form of heat or molecular 

 motion in the sun and planets in our immediate system 

 may bear, and probably does bear, a by no means inap- 

 pretiable ratio to that more distinctly patent in the form 

 of bodily motion in the periodical circulation of the 

 planets round the sun, and the sun and planets round 



