NATURAL PHILOSOPHY. 123 



accomplished when we wind up our clocks and watches. The man who 

 winds the clock or watch communicates to the weight or to the spring a 

 certain amount of power, and exactly 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 

 Avheels 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 our 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 pre- 

 viously 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 communicate to it by the unaided effort of the arm in throwing ii. 



From these examples you observe, and the mathematical theory has cor- 

 roborated this for all purely mechanical, that is to say, for moving forces, 

 that all our machinery and apparatus gcnerat3 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 perpetual 

 motion, which should only make use of pure mechanical forces, such as 

 gravity, elasticity, pressure of liquids and gases, could only be sought after 

 by bewildered and ill-instructed people. But there are still other natural 

 forces which are not reckoned among the purely moving forces, heat, 

 electricity, magnetism, light, chemical forces, all of which nevertheless stand 

 in manifold relation to mechanical processes. There is hardly a natural 

 process to be found which is not accompanied by mechanical actions, or 

 from which mechanical work may not be derived. Here the question of a 

 perpetual motion remained open ; the decision of this question marks the 

 progress of modern physics. 



In the case of the air-gitn, the work to be accomplished in the propulsion 

 of the ball was given by the arm of the man who pumped in the air. In 

 ordinary firearms, the condensed mass of air which propels the bullet is ob- 

 tained in a totally different manner, namely, by the combustion of the pow- 

 der. Gunpowder is transformed by combustion for the most part into gas- 

 eous products, which endeavor to occupy a much larger space than that 

 previously taken up by the volume of the powder. Thus, you see, that, by 

 the use of gunpowder, the work which the human arm must accomplish in 

 the case of the air-gun is spared. 



