1 2 Qn Machines in General. 



inent should always change by imperceptible degrees; which 

 occasions, among other things, some remarks upon hy- 

 draulic machines. 



Finally, L terminate this production by some reflection!* 

 upon the fundamental laws of the communication of move- 

 ment, which, if they be not agreeable to every body, have at 

 least the merit of brevity. 



I repeat that this Essay has merely for its object machi- 

 nery in general ; each machine has its peculiar properties : 

 here we have only to do with those which are common to 

 all ; these properties, although sufficiently numerous, are in 

 some measure all comprehended in one very simple law : 

 it is this law I purpose to explain, to demonstrate, and de- 

 velop, always regarding machines under the most general 

 and direct point of view. 



Introduction. 



I. There is no want of excellent treatises upon machi- 

 nery : the properties peculiar to those in frequent use, and 

 particularly to those called simple, have been inquired after 

 and expounded with all possible sagacity. In my opinion, 

 however, too little attention has been bestowed in the de- 

 velopment of those iproperties which are common to ma- 

 chinery in general, and which for this reason no more 

 belong to the cords of a machine than to the lever, the 

 vice, or any other machine, whether simple or com- 

 pound. 



It is not, however, because geometricians have neglected 

 to ascend to the general principles of equilibrium or move- 

 ment ; but it is only, as it were, en passant that they have 

 spoken of their application to the' theory of machines pro- 

 perly so called : and perhaps there is none of these prin- 

 ciples to be found whteh unites to a rigorous demonstration 

 a sufficient generality, to make it answer solely and in- 

 dependently for the solution of the various questions which 

 may be proposed, as well upon the equilibrium as upon the 

 movement of machines, i. e. for reducing every question to 

 a business of geometry and calculation ; — this is the true 

 object of mechanics. 



II. Among 



