SCIENTIFIC RECREATIONS. 



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No body can give unlimited work, therefore the perpetual motion theory is 

 untenable and impossible. 



The pendulum is considered the nearest 

 approach to perpetual motion. This is so well 

 known that no description is needed, but we may 

 say a few words concerning it. By the diagram, 

 we see that if we lift the ball to b, and let it fall, 

 it will .descend to /, and pass it to a opposite, 

 nearly as far from / as b is from it. So the oscil- 

 lations will continue, each beat being less and less, 

 till rest is reached by the action of gravity (page 

 23). Were it not for friction and the pressure of 

 the air, the oscillations would continue for ever ; 

 as it is, it declines by shorter swings till it remains in equilibrium. 



The seconds' pendulum oscillates sixty times an hour, and must be of 

 a certain length in certain places. In London it is 39*1393 inches, and 

 furnishes a certain standard of length, and by an Act of Parliament the yard 

 is divided into 36 parts, and 39*1393 such parts make the seconds' pendu- 

 lum in the latitude of London (in vacuo) in a temperature of 62. 



Fig. 35. The pendulum. 



Fig. 36. Centrifugal Force. 



But the same pendulum will not perform the same number of oscilla- 

 tions in one minute in all parts of the globe. At the equator they will be 



