278 CLASSICS OF MODERN SCIENCE 

 time. In practice, indeed, this ratio is by no means attained ; a gretic 

 portion of the work of the falling water escapes unused, inasmuch as 

 part of the force is unwillingly sacrificed for the sake of obtaining 

 greater speed. 



I will further remark, that this relation remains unchanged whether 

 the hammer is driven immediately by the axle of the wheel, or whether 

 — by the intervention of wheel- work, endless screws, pulleys, ropes; — 

 the motion is transferred to the hammer. We may, indeed, by such 

 arrangements, succeed in raising a hammer of ten hundred weight, 

 Vv'hen by the first simple arrangement, the elevation of a hammer of 

 one hundred weight might alone be possible; but either this heavier 

 hammer is raised to only one-tenth of the height, or tenfold the time 

 is required to raise it to the same height; so that, however we may 

 alter, by the interposition of machinery, the intensity of the acting 

 force, still in a certain time, during which the mill-stream furnishes us 

 with a definite quantity of water, a certain definite quantity of work, 

 and no more, can be performed. 



Our machinery, therefore, has, in the first place, done nothing more 

 than make use of the gravity of the falling water in order to overpower 

 the gravity of the hammer, and to raise the latter. When it has lifted 

 the hammer to the necessary height, it again liberates it, and the ham- 

 mer falls upon the metal mass which is pushed beneath it. But why 

 does the falling hammer here exercise a greater force than when it is 

 permitted simply to press with its own weight on the mass of metal? 

 Why is its power greater as the height from which it falls is increased ? 

 We find, in fact, that the work performed by the hammer is de- 

 termined by its velocity. In other cases, also, the velocity of moving 

 masses is a means of producing great eflfects. I only remind you of 

 the destructive effects of musket-bullets, which, in a state of rest, are 

 the most harmless things in the world. I remind you of the wind- 

 mill, which derives its force from the moving air. It may appear 

 surprising that motion, which we are accustomed to regard as a non- 

 essential and transitory endowment of bodies, can produce such great 

 effects. But the fact is, that motion appears to us, under ordinary 

 circumstances, transitory, because the movement of all terrestrial 

 bodies is resisted perpetually by other forces, friction, resistance of 

 the air, etc., so that motion is incessantly weakened and finally neu- 

 tralized. A body, however, which is opposed by no resisting force, 



