THE ORGANISM AS A MECHANISM 59 



formation of this accumulated potential energy, and 

 the reader will notice the analogy of all this with the 

 essential, unconsciously expressed activity of the animal 

 organism in its own metabolism — a point to which 

 we return later. 



Notice now that all the energy-transformations 

 we have noticed are irreversible. This is a matter of 

 deep philosophical importance, and we must devote 

 some time to it. Consider first of all the working of 

 the steam-engine ; what occurs is this — coal is burned 

 in the boiler-furnace, that is to say, potential chemical 

 energy passes into heat and this vaporises water in 

 the boiler, producing a gas at high temperature (steam.) . 

 This gas expands in the high-pressure cylinder of the 

 engine, driving forward a piston ; it expands further in 

 the intermediate cylinder, propelling its piston also, 

 and again in the low-pressure cylinder. It is then 

 cooled by passing through the condenser, and in the 

 contraction further mechanical energy is obtained. 

 The train of events thus begins with a gas at a high 

 temperature and ends with the same gas at the tem- 

 perature of the water in the condenser. The heat 

 lost is transformed into the mechanical energy of the 

 engine. But not all of it. A certain quantity is lost 

 by radiation from the boiler walls, the walls of the 

 steam-pipes, the cylinders, and other parts of the engine ; 

 also some of the energy is transformed to friction, 

 and this again to heat. In this way a very considerable 

 part of the energy contained in the coal is frittered 

 away in unavoidable heat-conduction and radiation, 

 and a last residue of it goes down the drain, so to speak, 

 with the condenser water. This loss is inherent in the 

 nature of the mechanism of the engine. 



Suppose that the energy of the engine is employed 

 to drive a dynamo. The armature of the latter rotates 



