MECHANICS. 9& 



eommon centre of gravity, lines be drawn to every 

 one of the given points; the forces which draw 

 in a direction of these lines, and are proportional 

 te them, will be in equilibria. 



HUGENII, Opera varia, torn. i. p. 288. 



a. It follows from the above propositions, that by 

 means of a rope, a small power may be made to 

 raise a very great weight to a small height ; and 

 also, that if a rope is stretched horizontally between 

 two points, its own weight will prevent it from be- 

 coming perfectly straight, whatever force be employ- 

 ed to stretch it. The curve which a flexible chain 

 or cord forms, when suspended by its two extremi- 

 ties, and either hanging freely, or having any de- 

 gree of tension applied to it, is called the Catenaria. 



SECT. III. 



OF FRICTION. 



156. JJESIDES the resistance which the mecha- 

 nical powers, and the machines compounded of 

 them, are intended to overcome, an impediment to 

 their motion is always observed when the moving 

 parts are in contact with one another. This im- 

 pediment to motion is called Friction. 



The 



