THE ORGANISM AS A MECHANISM 81 



in waste heat now propel ships and windmills. Tides, 

 with their incredibly great mechanical energy, now 

 simply warm up the crust of the earth by an infini- 

 tesimal fraction of a degree daily, and produce heat 

 which at once radiates into space. Who doubts that 

 by and by this energy too will become accumulated 

 for human use ? Multitudes of chemical reactions 

 were potential, so to speak, in the molecules of 

 petroleum, while the energy which might have pro- 

 duced them ran to waste. But under human activity 

 this energy became directed and made to produce 

 chemical reactions formerly existing only in their 

 possibility, and all the substances of modern organic 

 chemistry came into existence. 



The energy, then, of human activity has been directed 

 towards averting or retarding the progress towards 

 dissipation, or irrecoverable waste, of cosmic energy — 

 that of the sun's radiation, and of the motions of 

 earth and moon. Human activity has accumulated 

 available energy. The difference of water-level 

 between Niagara and the rapids below represents 

 available mechanical energy. A few years ago an 

 enormous quantity of this energy became irredeemably 

 lost in waste heat every twenty-four hours : now it 

 remains available for work ; and this quantity of work 

 retained is enormously greater than is the human 

 energy which was expended on erecting the water- 

 power installation there. 



The processes studied by physics and chemistry 

 are therefore irreversible ones. We can conceive a 

 perfectly reversible process, as in the Carnot heat- 

 engine, but this is a purely intellectual conception, 

 formed as the limit to a series of operations which 

 approximate closer and closer to an ideal reversibility. 

 It is a conception that has no physical reality — a 



