HOW WORK IS DONE 



tongs, the treadle of a lathe, or by the flexor muscles of 

 the arm, operating upon the bones of the forearm. 



But in each case, let it be repeated, precisely the same 

 principles are involved, and the same simple law of the 

 relations between positions of power, weight, and ful- 

 crum are maintained. The practical result is always 

 that a weight of indefinite size may be moved by a power 

 indefinitely long. If one arm of the lever is ten times 

 as long as the other, the power of one pound will lift 

 or balance a ten-pound weight; if the one arm is a 

 thousand times as long as the other the power of one 

 pound will lift or balance a thousand pounds. If 

 the long arm of the lever could be made some mil- 

 lions of miles in length, the power that a man could 

 exert would balance the earth. 



How fully Archimedes realized the possibilities of 

 the lever is illustrated in the classical remark attributed 

 to him, that, had he but a fulcrum on which to place 

 his lever, he could move the world. As otherwise 

 quoted, the remark of Archimedes was that, had he 

 a place on which to stand, he could move the world, 

 a remark which even more than the other illustrates 

 the full and acute appreciation of the laws of motion; 

 since, as we have already pointed out, action and re- 

 action being equal, the most infinitesimal push must be 

 considered as disturbing even the largest body. 



Tremendous as is the pull of gravity by which the 

 earth is held in its orbit, yet the smallest push, steadily 

 applied from the direction of the sun, would suffice 

 ultimately to disturb the stability of our earth's motion, 

 and to push it gradually through a spiral course farther 



