34 



THE ANIMAL AS A MACHINE. 



as the rate per second of emission of energy from a square 

 foot of the sun's surface, equivalent to 7000 horse- 

 power,^ we find that more than 0.42 of a pound of coal 

 per second, or 1500 lbs. per hour, would be required 

 to produce heat at the same rate. Now if all the fires 

 of the whole Baltic fleet were heaped up and kept in 

 full combustion over one or two square yards of surface, 

 and if the surface of the globe all round had every square 

 yard so occupied, where could a sufficient supply of air 

 come from to sustain the combustion ? — yet such is the 

 condition we must suppose the sun to be in, according 

 to the hypothesis now under consideration, at least if 

 one of the combining elements be oxygen or any other 

 gas drawn from the surrounding atmosphere." 



12. The Forms of Motor, the special machines 

 through which these transfers and transformations are 

 effected, are the following : 



(1) The animal body is a vital machine, of extra- 

 ordinary complexity, self-constructing and self-repair- 

 ing, and is automatic in its many and usually mysterious 

 internal processes. 



This machine is directed by conscious intelligence 

 and will, and, when usefully applied to the production 

 of work, is guided by the mysterious action of the mind. 

 It effects conversions of energy through the processes 

 of chemical action peculiar to the animal system. 



(2) TJie heat-engines, including steam-, air-, gas-, and 

 vapor-engines of various less familiar kinds. 



In these machines, the potential energy of fuel is, by 

 combustion, converted into the active form, and stored 



* This is sixty-seven times the rate at which energy is emitted from 

 the incandescent electric lamp at the temperature which gives 240 

 candles per horse-power. 



