DISCOVERY OF THE LAWS OF MOTION. 41 



properties of machines by means of this principle. 

 This is done, for instance, in Les Raisons des 

 Forces Mouvantes, the production of Solomon de 

 Caus, engineer to the Elector Palatine, published at 

 Antwerp in 1616; in which the effect of toothed- 

 wheels and of the screw is determined in this 

 manner, but the inclined plane is not treated of. 

 The same is the case in Bishop Wilkins's Mathe- 

 matical Magic, in 1648. 



When the true doctrine of the Inclined Plane 

 had been established, the laws of equilibrium for 

 all the simple machines or Mechanical Powers, as 

 they had usually been enumerated in books on 

 Mechanics, were brought into view ; for it was easy 

 to see that the wedge and the screw involved the 

 same principle as the inclined plane, and the pulley 

 could obviously be reduced to the lever. It was, 

 also, not difficult for a person with clear mecha- 

 nical ideas, to perceive how any other combination 

 of bodies, on which pressure and traction are 

 exerted, may be reduced to these simple machines, 

 so as to disclose the relation of the forces. Hence 

 by the discovery of Stevinus, all problems of equili- 

 brium were essentially solved. 



The conjectural generalization of the property 

 of the lever, which we have just mentioned, enabled 

 mathematicians to express the solution of all these 

 problems, by means of one proposition. This was 

 done by saying, that in raising a weight by any 

 machine, we lose in time what we gain in force ; 



