300 On Machines in General. 



movemenl, except by insensible degrees ; — we must solely 

 except those which by their very nature are subject to un- 

 dergo different percussions, like most kinds of mills ; but 

 even in this case, it is clear that we should avoid every sud- 

 den change which is not essential to the constitution of the 

 machine. 



LIX. We may conclude from this, for example, that the 

 method of producing the greatest possible effect in a hy- 

 draulic machine moved by a current of water, is not to 

 adapt a wheel to it, the wings of which receive the shock 

 of the iluid. In fact, two good reasons prevent us from pro- 

 ducing in this way the greatest effects : the first is, as we 

 have already said, because it is essential to avoid every kind 

 ol" percussion whatever ; the second is, because after the 

 shock of the fluid there is still a velocity which remains to 

 it as a pure loss, since we sliould be able to employ this 

 remainder in still producing a new effect to be added to the 

 first. In order to make the most perfect hydraulic machine, 

 I. e. capable of producing the greatest possible effect, the 

 true difficulty lies, 1st, In managing so as that the fluid may 

 lose abcoluiely all its movement by its action upon the ma- 

 chine, or at least that there should only remain precisely the 

 quantity necessary for escaping after its action ; 2d, Another 

 difficuhy occurs in so far as it loses all this movement by 

 insensible degrees, and without there being any percussion, 

 either on the part of the fluid, or on the part of the solid 

 parts among themselves : the form of the machine would be 

 of little consequence ; for a hydraulic machine which will 

 fulfd these two conditions will always produce the greatest 

 possible eff"ect : but this ))rol)!tm is very difficult to resolve 

 ill general, not to say impossible; it may even happen that 

 in the physical state of things, and in respect of their sim- 

 plicity, there can be nothing btttiT than wheels moved by 

 shocks : and in this case as it \.- impossible to fulfil at once 

 the two conditions most desirable, the more we wish to 

 make, the fluid lose of its movement in order to attain the 

 first condition., the stronger will be the shock ; the more, on 

 the contrary, .ve wish to moderate the shock in order to ap- 

 proach the second, the less will the fluid lose of its move- 

 ment. 



