OF THE MECHANICAL POWEl'.S 



69 



at A. The reason why the machine must be drawn 

 further than the whole length C B is, because the weight 

 F rises perpendicular to C B. 



To the inclined plane may be reduced all hatchets, 

 chisels, and other edge-tools which are chamfered only 

 on one side. 



5. The fifth mechanical power or machine is the 

 wedge, which may be considered as two 

 equally inclined planes D E .Fand CE F, 

 joined together at the bases e E F O : 

 then D C is the whole thickness of the 

 wedge at its back A B C D, where the 

 power is applied : E F is the depth or 

 height of the wedge : D F the length of 

 one of its sides, equal to C jF the length 

 of the other side ; and O JF is its sharp 

 edge, which is entered into the wood in- 

 tended to be split by the force of a ham- 

 mer or mallet striking, perpendicularly 

 on its back. Thus, A B b is a wedge 

 driven into the cleft C D E of the wood 



LECT. 

 III. 



\\ hen the wood does not cleave at any distance be- 

 fore the wedge, there will be an equilibrium between 

 the power impelling the wedge downward, and the re 

 sistance of the wood acting against the two sides ol 

 the wedge when the power is to the resistance, as half 

 the thickness of the wedge at its back is to the length 

 of either of its sides ; because the resistance then acts 

 perpendicular to the sides of the wedge. But, when the 

 resistance on each side acts parallel to the back, the 

 power that balances the resistances on both sides will 

 oe as the length of the whole back of the wedge is to 

 double its perpendicular height. 



When the wood cleaves at any distance before the 

 wedge (as it generally does) the power impelling the 



The 

 wedge. 



