GRAVISTATIC HEAT 337 



of the machine, the nature of the materials employed and 

 the intensity of the pressure applied. 



With this wonderful and inexhaustible source of en- 

 ergy at command mankind can reckon calmly on the fu- 

 ture, and view with equanimity the hitherto terrifying 

 prospect that our present visible supplies of unmined 

 coal will become exhausted within the next two centuries. 

 By pressure coolness, too, can be produced, though not to 

 corresponding extremes, by merely allowing water to 

 cool to its lowest point of density and, while in that state, 

 stoutly confining it against future expansion.In this con- 

 nection, permit another quotation from Professor 

 Stewart (Conservation of Energy, pp. 118, 119) : 



It may be shown that if the proposition (of conservation) be 

 true, under certain test conditions we ought to obtain certain re- 

 sults for instance, if we increase the pressure, we ought to 

 lower the freezing point of water. Well, we make the experiment 

 and find that, in point of fact, the freezing point of water is low- 

 ered by increasing the pressure, and we have thus derived an 

 argument in favor of the conservation of energy. 



Or again, if the laws of energy are true, it may be shown 

 that whenever a substance contracts when heated, it will become 

 colder instead of hotter by compression. Now, we know that 

 ice-cold water or .water just a little above its freezing point, con- 

 tracts instead of expanding up to 4 C; and Sir William Thomp- 

 son has found by experiment that water at this temperature is 

 cooled instead of heated by sudden compression. 



Let us scan the claim Mr. Stewart makes that this 

 instance he speaks of is a " proof of conservation." In 

 the first place, it will not be denied by any Conservation- 

 ist that the work done in turning the compression screw 

 is equatable in terms of units of thermal energy. Sup- 

 pose, now, that a flame were applied to the container un- 

 til the water was restored to the temperature it had prior 

 to compression, and the clamp then released. What now 

 would be the state of our dynamics account in profit and 

 loss in terms of units of energy? On the side of profits 

 there would be positively nothing, while the losses would 

 be treble, and include the mechanical energy of clamping, 

 of unclamping, and the heat of the flame yet the status 

 at the end would be precisely what it was at the outset I 



