172 ELEMENTS OF GENERAL SCIENCE 



of the latter to help themselves in getting this work done. 

 In this chapter we shall study about work and the means of 

 accomplishing it. 



190. Different methods of working. When our ancestors 

 were living in a state of savagery, as they did many centu- 

 ries ago, their ways of working were doubtless as primitive 

 as the methods in use at the present time among some sav- 

 age tribes. The first men doubtless did everything with their 

 unaided hands, but soon they learned that a heavy object 

 could be pried up with a stick more easily than it could be 

 lifted by the hands, that a sling would throw a stone harder 

 than the unaided hand, that a log could be rolled up an in- 

 cline if it was too heavy to be lifted, and that an arrange- 

 ment of rope and pulleys would make it possible to hoist very 

 heavy weights by the use of small force. Gradually the more 

 intelligent part of mankind has developed the use of simple 

 machines and combinations of them, until now there is scarcely 

 any work done without the use of some sort of mechanical 

 contrivance. The simple machines, which are the basis of the 

 devices which we employ to assist us in working, are the lever, 

 the pulley, the inclined plane, the wheel and axle, the screw, 

 and the wedge. 



The knowledge of the use of machines is of great value to 

 civilized man. If we had been compelled to depend on bare 

 hands and our own physical strength alone for accomplishing 

 all sorts of work, our present civilization could not have de- 

 veloped. We should be in very much the state of the tribes 

 in those parts of Africa, Asia, and Australia where the soil is 

 dug with a stick and goods are transported on the backs of 

 men. The use of various contrivances which assist in the ac- 

 complishment of work, and the knowledge of their possibili- 

 ties, are among the marks which distinguish civilized people 

 from savages. 



191. A problem in work. If a savage wishes to remove his 

 dugout canoe from the water, he knows no way to do so but 



