THE CONQUEST OF NATURE 



much more powerful blow than with the shorter lever 

 of the flexed arm. But however ingenious the manipu- 

 lation of the natural levers, a full utilization of muscu- 

 lar energy is possible only when they are supplemented 

 with artificial aids, which constitute primitive pieces of 

 machinery. 



These aids are chiefly of three types, namely, in- 

 clined planes, friction reducers, and levers. The use 

 of the inclined plane was very early discovered and 

 put into practise in chipped implements, which took 

 the form of the wedge, in such modifications as axes, 

 knives, and spears of metal. All of these implements, 

 it will be observed, consist essentially of inclined planes, 

 adapted for piercing relatively soft tissues of wood or 

 flesh, and hence serving purposes of the greatest prac- 

 tical utility. 



The knife-blade is an extremely thin wedge, to be 

 utilized by force of pushing, without any great aid from 

 acquired momentum. The hatchet, on the other hand 

 and its modification the axe has its blunter blade 

 fastened to a handle; that the principle of the wedge 

 may be utilized at the long end of a lever and with the 

 momentum of a swinging blow. Ages before anyone 

 could have explained the principle involved in such 

 obscuring terms as that, the implement itself was in use 

 for the same purpose to which it is still applied. Indeed, 

 there is probably no other implement that has played 

 a larger part in the history of human industry. Even 

 in the Rough Stone Age it was in full favor, and the 

 earliest metallurgists produced it in bronze and then 

 in iron. The blade of to-day is made of the best tern- 



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