THE CONQUEST OF NATURE 



sizes of the wheels, and not the length of the belt or 

 chain, is the determining factor as regards the relative 

 forces required to make the wheels revolve. 



It is obvious all along, of course, since action and 

 reaction are equal, that all of the relations in question 

 are reciprocal. When, for example, we speak of a 

 pound weight on the long end of a lever balancing a ten- 

 pound weight on the short end, it is equally appropriate 

 to speak of the ten-pound weight as balancing the one- 

 pound weight. Similarly, when power is applied to 

 the lever, it may be applied at either end. Ordinarily, 

 to be sure, the power is applied at the long end, since 

 the object is to lift the heavy weight; but in complicated 

 machinery it quite as often happens that these condi- 

 tions are reversed, and then it becomes desirable to 

 apply strong power to the short end of the lever, in 

 order that the relatively small weight may be carried 

 through the long distance. In the inter-relations of 

 gearing wheels, such conditions very frequently obtain, 

 practical ends being met by a series of wheels of differ- 

 ent sizes. But the single rule, already so often out- 

 lined, everywhere holds wherever there is gain of 

 power there is loss of distance, and we can gain distance 

 only by losing power. The words gain and loss in this 

 application are in a sense misnomers, since, as we have 

 already seen, gain and loss are only apparent, but 

 their convenience of application is obvious. 



A familiar case in which there is first loss of speed 

 and gain of power, and then gain of speed at the ex- 

 pense of power in the same mechanism, is furnished 

 by the bicycle, where (i) the crank shaft turns the 



[36] 



