CHAPTER IX 



A PERFECT LUBRICATING SYSTEM 



We are now to see how a certain difficulty, one which 

 taxes the ingenuity of designers of all kinds of moving 

 machines, has been successfully surmounted in the con- 

 struction of the human body. The difficulty is that of 

 making one part rub or move on another — the piston 

 within its cylinder, the axle within its bush — with the 

 least amount of friction, and therefore with the least 

 waste of power. No matter how truly a shaft is made 

 and set within its bushes, or how perfectly the shaft may 

 revolve within its bearings, friction of the grossest kind 

 will still be produced, with the result that the engine 

 wastes its power in making its joints red-hot, thus 

 ruining the essential parts of its machinery. But if we 

 separate the shaft from its bearings by a coating of oil 

 and succeed in maintaining that coating in place, then 

 friction will be reduced to a minimum ; the bushes 

 remain cool, and the power of the engine is expended 

 in work. The ideal system which engineers seek to dis- 

 cover is one which will maintain a delicate and uniform 

 film of oil between moving surfaces. The particles of the 

 oil film act as microscopic ball-bearings, on which the 

 revolving shaft turns. But the ideal system is difficult to 

 come by for two reasons : (i) every shaft or axle tends to 

 squeeze the film from that part of the bearings on which 

 the pressure is greatest — just the situation where the film 

 is most needed ; (2) the film is constantly wasting from 

 such friction as is unavoidable, hence this waste has 

 steadily to be made good. 



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