44 MECHANIC POWERS. 



Let A B (Fig. 3.) be a plane parallel to the hori- 

 zon, and A D a plane inclined to it; and suppose 

 the whole length A D to be three times as great as 

 the perpendicular D B. In this case, the cylinder 

 E will be supported upon the plane D A, and kept 

 from rolling, by a power equal to a third part of 

 the weight of the cylinder; therefore a weight may 

 be rolled up in this inclined plane by a third part 

 of the power which would be sufficient to draw it 

 up by the side of an upright wall. 



It must also be evident, that the less the angle 

 of elevation, or the gentler the ascent is, the 

 greater will be the weight which a given power 

 can draw up; for the steeper the inclined plane is, 

 the less does it support of the weight; and the 

 greater the tendency which the weight has to roll, 

 consequently the more difficult for the power to 

 support it: the advantage gained by this mechanical 

 power, therefore, is as great as its length exceeds 

 its perpendicular height. 



To the inclined plane may be reduced all hat- 

 chets, chisels, and other edge-tools. 



THE WEDGE. 



The wedge may be considered as two equally 

 inclined planes, joined together at their bases; then 

 D C (Plate 3. fig. 4.) 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; 

 B F the length of one of its sides; and O F is its 

 sharp edge, which is entered into the wood intended 

 to be split by the force of a hammer or mallet 

 striking perpendicularly on its back. Thus, A B 

 (Fig. 5.) is a wedge driven into the cleft C E D of 

 the wood F G. 



When the wood does not cleave at any distance 

 before the wedge, there will be an equilibrium be- 



