MECHANICS. 87 



another, arid one of them parallel to the back of the 

 wedge, or the side to which the power is applied. 

 In the case of equilibrium, the opposite forces, in 

 the direction of these axes, must be equal to one 

 another. In this way the following theorems are 

 easily investigated. 



145. When three forces are applied perpendicu- 

 larly to the three faces of a triangular prism or 

 wedge, they will be in equilibria, if their directions 

 intersect in the same point, and if they are to ohe 

 another as the lengths of the sides to which they 

 are applied. 



146. If the resistance to the motion of an isos- 

 celes wedge be perpendicular to the back of the 

 wedge, there will be an equilibrium, when the pow- 

 er applied to the back of the wedge is to the 

 sum of the resistances, as the thickness of the back 

 to twice the height of the wedge ; and therefore if 

 the bodies are equal, the power will be to the resis- 

 tance of either of them, as half the base of the 

 wedge to the height of it. 



This proposition is most easily demonstrated on the 

 principle of the virtual velocities, ( 127. b.) 



If one of the resisting bodies only is moveable, the 

 power will be to the resistance as the base of the 

 wedge to its height. 



The 



