A WILD THEORY. 



65 



modes of using the lever, as we have already seen, depends 

 on the difference between the lengths of its two arms. A 

 yoke of oxen, drawing with a force of 500 pounds on the 

 long arm of a lever 25 feet long, will exert a force on the 

 short arm of six inches equal to 50 times 500 pounds, or 

 25,000 pounds, on the stump. 



It was after an examination of the great power which 

 may be given to the lever by increasing this difference 

 that Archimedes exultingly exclaimed, " Give me but a 

 fulcrum whereon to place my 

 lever, and I will move the earth !" 

 Admitting the theoretical truth of 

 this exclamation, and supposing 

 there could be a lever which he 

 might have used for this purpose, 

 its practical impossibility may be \ 



Fig. 56. 



quickly understood by computing 

 the whole bulk of the globe ; for 

 such is its enormous size and cu- 

 bical contents, that Archimedes 

 must have moved forward his 

 lever with the strength of a hun- 

 dred pounds and the swiftness 

 of a cannon ball for eight hundred million years to have 

 moved the earth the thousandth part of an inch ! 



WHEEL AXD AXLE. 



In treating of the lever, it was shown to be capable of 

 exerting a force through a small distance only. Hence, 

 if a heavy body were required to be elevated to any con- 

 siderable height, it would be necessary to accomplish it 

 by a succession of efforts. This inconvenience is removed 

 by a constant and unremitted action of the lever in the 

 form of the wheel and adcle. 



Let the weight, ic (fig. 56,) be suspended by a cord 



