WHEEL AND AXLE. 75 



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 dif- 

 ference that Archimedes exultmgly exclaimed, " Give 

 me but a fulcrum whereon to place my lever, and I 

 will move the earth !" Admitting the theoretical truth 

 of tliis exclamation, and supposing there could be a 

 lever which he might have used for this purpose, its 

 practical impossibility may be quickly understood by 

 computing the whole bulk of the globe ; for such is 

 its enormous size and cubical contents, that Archim- 

 edes must have moved forward his lever with the 

 strength of a hundred pounds and the swiftness of a 

 cannon ball for eight hundred million years to have 

 moved the earth the thousandth part of an inch ! 



SECTION IV. 

 WHEEL AND AXLE. 



In treating of the lever, it was shown to be capa- 

 ble of exerting a force through a small distance only. 

 Hence, if a heavy body were required to be elevated 

 to any considerable height, it would be necessary to 

 accomplish it by a succession of efforts. This incon- 

 venience is removed by a constant and unremitted 

 action of the lever in the form of the ivheel and axle. 



Let the weight, w {Fig. 56, p. 76), be suspended by 

 a cord from the end of the lever, a b, and a wheel at- 

 tached to the lever, so that this cord may wind upon 

 it as the weight is elevated ; then let the power be ap- 

 plied at the other end by means of a cord, and a larger 



