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 

 possibilit3^ and ail the substances of modem organic 

 chemistry came into existence. 



The energ}^ 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 



