258 Introduction to the Study of Science 



These few applications of the principle of the lever may 

 suffice to indicate its importance to man. The mechanical 

 advantages were probably first studied and described by the 

 ancient Greek mathematician and scientist, Archimedes (about 

 287-212 B.C.), who in his enthusiasm over its importance de- 

 clared that if he had " a place whereon to stand " and apply 

 his lever, he could move the world. From this it is evident 

 that inventors in primitive ages devised in the lever a most 

 useful machine. Its utility, in whatever form it may be em- 

 bodied, lies in the fact that it gives man with his limited power 

 a great advantage in overcoming resistance or weight. This 

 is true whether it is employed in moving heavy bodies or in 

 doing other kinds of work. Through his ingenuity man has 

 turned the principle of this simple machine to all sorts of com- 

 plex and intricate uses in machines ranging from the ordinary 

 pry to the windlass, the watch, the steam shovel, and the loco- 

 motive. 



107. Friction. The use of the drag as a vehicle leads 

 directly to the discovery that a heavy load can be moved more 

 easily over a smooth surface than over a rough. Dragging 

 may be made easier by means of sled runners ; but with the 

 use of runners there must be some improvement of the trails 

 or roads over which heavy loads are frequently dragged or 

 hauled. It is a clearly recognized advantage to reduce as much 

 as possible the resistance encountered in moving heavy loads 

 over roads. To-day such resistance is generally known as 

 sliding friction. Thus progress in road making is intimately 

 associated with improvements in vehicles ; both being designed 

 to reduce sliding friction to the minimum. 



The wheel and axle. One of the most important discoveries,- 

 ranking with that of fire and of the bow and arrow, was the 

 wheel which turns on a shaft or axle. To make the ends of 

 poles or the runners of a sled or drag slide over rough or soft 

 earth, was far from easy, and it required great strength for 

 heavy loads and allowed only a slow rate of progress in favor- 



