THE ANIMAL MACHINE 



record those, namely, of Old Egypt and of Old Baby- 

 lonia in full possession of the principle of the wheel 

 as applied to vehicles. Modern mechanics have, of 

 course, improved the mechanism as regards details, 

 but the wheels depicted in Old Egyptian and Babylonian 

 inscriptions are curiously similar to the most modern 

 types. Indeed, the wheel is a striking illustration 

 of a mechanism which continued century after century 

 to serve the purposes of the practical worker, with seem- 

 ingly no prospect of displacement. 



MODIFIED LEVERS 



For the rest, the mechanisms which primitive man 

 learned early to use in adding to his working efficiency, 

 and which are still used by the hand laborer, are vir- 

 tually all modifications of our familiar type-implement, 

 the lever. A moment's reflection will show that the 

 diversified purposes of the crowbar, hoe, shovel, ham- 

 mer, drill, chisel, are all accomplished with the aid of 

 the same principles. The crowbar, for example, 

 enables man to regain the power which he lost when 

 his members were adapted to locomotion. His hands, 

 left to themselves, as we have already pointed out, give 

 but inadequate expression to the power of his muscles. 

 But by grasping the long end of such a lever as the 

 crowbar, he is enabled to utilize his entire weight in 

 addition to his muscular strength, and, with the aid 

 of this lever, to lift many times his weight. 



The hoe, on the other hand, becomes virtually a 

 lengthened arm, enabling a very slight muscular motion 



[57] 



