THE MACHINES OF THE ANCIENT WORLD 15 



simple machines and partly in their organization of 

 society. They were familiar, we know, with some or 

 all of six mechanical contrivances, known as the six 

 simple machines. These are the lever, the inclined 

 plane, the wedge, the pulley, the screw, and the wheel 

 and axle, conventionally illustrated hi Fig. 3. Let 

 us see what the advantages of these devices would be. 



The lever consists of a bar. If the distance from the 

 fulcrum, Cj to the point a, where the force is applied, 



FIG. 3.. 



is larger than that to the point b, then, as we know, the 

 lever gives a mechanical advantage. The force ex- 

 erted at 6 by the lever is as many times greater than 

 the force applied at a as the distance ac is greater than 

 be. It was not until the time of Archimedes (died 

 212 B.C.) that men knew this rule. During preceding 

 centuries, however, they must have had a very good 

 working knowledge of the lever. 

 When a man wanted to raise the end of a block of 



