CHAPTER XV 



MAN'S INVENTIONS FOR TRANSFERRING AND TRANS- 

 FORMING ENERGY 



Tools. Primitive man early found that it was to his 

 advantage to use something besides his own hands and feet 

 to apply his energy. Probably the first tool that he used 

 was a stone which he threw at some animal he wished to 

 kill for food. Soon he found * 



that if he put the stone in 

 a strip of hide and swung 

 it around his head, he could 

 send it with greater force. 

 Thus he invented the sling, 

 probably the first device 

 for transferring energy and 

 the first war machine. 



Since then he has not 

 only invented many ma- 

 chines that have enabled 

 him to exert his own physi- 

 cal energy to greater advantage, but he has also devised 

 machines which make it possible for him to use the energy 

 that exists in the world about him. This ability to utilize 

 the energy of nature has made the life of modern man very 

 different from that of his 'savage ancestors. Without ma- 

 chines there could be no large cities, no manufacturing, 



459 



MAN'S FIRST WAR MACHINE 



