RESERVOIR OF ACCUMULATED POWER. 219 



weight or to the spring a certain amount of power, and ex- 

 actly so much as is thus communicated is gradually given out 

 again during the following twenty-four hours, the original 

 force being thus slowly consumed to overcome the friction of 

 the wheels and the resistance which the pendulum encounters 

 from the air. The wheel-work of the clock therefore exhibits 

 no working force which was not previously communicated to 

 it, but simply distributes the force given to it uniformly over 

 a longer time. 



Into the chamber of an air-gun we squeeze, by means of 

 a condensing air-pump, a great quantity of air. When we 

 afterwards open the cock of a gun and admit the compressed 

 air into the barrel, the ball is driven out of the latter with a 

 force similar to that exerted by ignited powder. Now we 

 may determine the work consumed in the pumping-in of the 

 air, and the living force which, upon firing, is communicated 

 to the ball, but we shall never find the latter greater than the 

 former. The compressed air has generated no working force, 

 but simply gives to the bullet that which has been previously 

 communicated to it. And while we have pumped for perhaps 

 a quarter of an hour to charge the gun, the force is expended 

 in a few seconds when the bullet is discharged ; but because 

 the action is compressed into so short a time, a much greater 

 velocity is imparted to the ball than would be possible to com- 

 municate to it by the unaided effort of the arm in throw- 

 ing it. 



-From these examples you observe, and the mathematical 

 theory has corroborated this for all purely mechanical, that is 

 to say, for moving forces, that all our machinery and appara- 

 tus generate no force, but simply yield up the power com- 

 municated to them by natural forces, falling water, moving 

 wind, or by the muscles of men and animals. After this law 

 had been established by the great mathematicians of the last 

 century, a perpetual motion, which should make only use of 

 pure mechanical forces, such as gravity, elasticity, pressure of 



