NATURAL PHILOSOPHY. 129 



Tims, in our steam engines, we convert a portion of the heat of the glowing 

 coal into work, by permitting it to pass to the less warm water of the boiler. 

 If, however, all the bodies in nature had the same temperature, it would be 

 impossible to convert any portion of their heat into mechanical work. Ac- 

 cording to this, we can divide the total force store of the universe into two 

 parts, one of which is heat, and must continue to be such ; the other, to 

 which a portion of the heat of the warmer bodies, and the total supply of 

 chemical, mechanical, electrical, and magnetical forces belong, is capable of 

 the most varied changes of form, and constitutes the whole wealth of 

 change which takes place in nature. 



But the heat of the warmer bodies strives perpetually to pass to bodies 

 less warm by radiation and conduction, and thus to establish an equilibrium 

 of tcmpei-ature. At each motion of a terrestrial body, a portion of mechan- 

 ical force passes by friction or collision into heat, of which only a part can 

 be converted back again into mechanical force. This is also generally the 



* 



case in every electrical and chemical process. From this, it follows that the 

 first portion of the store of force, the unchangeable heat, is augmented by 

 every natural process, while the second portion, mechanical, electrical, and 

 chemical force, must be diminished ; so that if the universe be delivered 

 over to the undisturbed action of its physical processes, all force will finally 

 pass into the form of heat, and all heat come into a state of equilibrium. 

 Then all possibility of a further change would be at an end, and the com- 

 plete cessation of all natural processes must set in. The life of men, ani- 

 mals, and plants, could not of course continue if the sun had lost its high 

 temperature, and with it his light, if all the components of the earth's sur- 

 face had closed those combinations which their affinities demand. In short, 

 the universe from that time forward would be condemned to a state of eter- 

 nal rest. 



These consequences of the law of Carnot are, of course, only valid, pro- 

 vided that the law, when sufficiently tested, proves to be universally correct. 

 In the mean time there is little prospect of the law being proved incorrect. 

 At all events we must admire the sagacity of Thomson, who, in the letters 

 of a long known little mathematical formula, which only speaks of the 

 heat, volume, and pressure of bodies, was able to discern consequences 

 which threatened the universe, though certainly after an infinite period of 

 time, with eternal death. 



I have already given you notice thai our path lay through a thorny and 

 un re freshing field of mathematico-mechanicak developments. ~\Ve have 

 now left this portion of our road behind us. The general principle which I 

 have sought to lay before you has conducted us to a point from which our 

 view is a wide one, and, aided by this principle, we can now at pleasure re- 

 gard this or the other side of the surrounding world, according as our inter- 

 est in the matter leads us. A glance into the narrow laboratory of the phy- 

 sicist, with its small appliances and complicated abstractions, will not be so 

 attractive as a glance at the wide heaven above us, the clouds, the rivers, 

 the woods, and the living beings around us. While regarding the laws 

 which have been deduced from the physical processes of terrestrial bodies, as 



