MECHANICS. 73 



a. If the props be A, B, C, (fig. 8.), and if W 

 be placed with its centre of gravity at D, and 

 if ADG, BDF, CDE, be drawn, the pressure 



When D coincides with the centre of gravity of the 

 triangle ABC, the pressure on each of the props is 

 the same. 



b. If W be supported by more than three props, the 

 problem appears to be indeterminate, or to admit of 

 innumerable solutions. 



Nevertheless, if the centre of gravity of W, as it 

 rests on the plane, be the same with the centre of 

 gravity of the figure made by joining the tops of the 

 props by straight lines, the pressures on the props 

 are all equal to one another. 



c. The lever is the simplest of the mechanical powers, 

 and appears to be the first that was attempted to be 

 explained. ARISTOTLE has treated of it in his Me- 

 chanical Questions, and has even endeavoured to re- 

 duce some other of the mechanical powers to the 

 lever. The first accurate explanation, however, 

 was given by ARCHIMEDES, Lib. i. de Equiponde- 

 rantibus, Prop. 6. 



d. The lever is used in mechanics in various forms and 

 combinations. The compound lever is, where one 



3 lever 



