162 ON THE INTERACTION OF NATURAL FORCES. 



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 the 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 com- 

 pressed air has generated no working force, but simply 

 gives to the bullet that which has been previously com- 

 municated to it. And while we have pumped for perhaps 

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

 pended 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 communicate to it by the unaided 

 effort of the arm in throwing it. 



From these examples you observe, and the mathe- 

 matical theory has corroborated this for all purely 

 mechanical, that is to say, for moving forces, that all our 

 machinery and apparatus generate no force, but simply 

 yield up the power communicated 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 per- 

 petual motion, which should make use solely of pure 

 mechanical forces, such as gravity, elasticity, pressure of 

 liquids and gases, could only be sought after by be- 

 wildered and ill-instructed people. But there are still 

 other natural forces which are not reckoned among the 

 purely moving forces, heat, electricity, magnetism, light, 



