58 OUTLINES OF NATURAL PHILOSOPHY. 



MECHANICS. 



SECT. I. 



OF THE CENTRE OF GRAVITY. 



104. IF a body fixed to a plane be preserved in 

 equilibria by a force having a given direction, and 

 attached also to a given point in the plane, it will 

 be kept in equilibria by the same force, when at- 

 tached to any other point whatever in the line of its 

 first direction. 



Let the force be attached by a thread to a given point 

 in the plane ; while the tension of the thread and 

 its direction continue, the equilibrium must conti- 

 nue. Suppose, then, that any other point in the 

 thread is fixed down to the plane, it is evident, that 

 the tension of the remaining part will not be changed 

 by that circumstance ; and therefore the equilibrium 

 must remain. 



C ARNOT has given a different proof of this proposition. 

 Prmcipes de T Eguilibre, &c. 77. 



105. If 



