[ I2 3 ] 
that they concluded the fame proportion between the 
power and refiftance would obtain in general. 
I have already mentioned the proportion which the 
power that drives the wedge mult have to the refift- 
ance in cleaving timber, when the wedge exactly fills 
the cleft ; which cafe however feldom happens ; for 
the wood generally fplits to fome di fiance before the 
wedge. And then, in order that there may be an 
aequilibrium between the power driving the wedge 
and the refiftance of wood, the former muft be to 
the latter, as the fine of half the vertical angle of 
the wedge, to the cofine of the angle which the fide 
of the cleft makes with the fide of the wedge. The 
truth of which is eafily underftood from what was 
proved in the third cafe of the wedge ; for the cofine 
of the angle, contained between the fide of the cleft 
and the fide of the wedge, is the fine of the angle 
which the fide of the wedge contains with the direc- 
tion in which the wood recedes j becaufe, as the cleft 
opens, the wood mull recede in lines perpendicular to 
the fides of the cleft ; and in the direction of thofe 
lines doth the refiftance of the wood adt on the fides 
of the wedge. 
The inclined plane is reckoned by fome writers 
among the mechanic powers; and I think with rea- 
fon, as it may be ufed with advantage in raifing 
weights. * 
Let the Line A B [Tab. VI. Fig. 4.] reprefent the 
length of an inclined plane, AD its height, and the line 
BD we may call its bafe. Let the circular body GEF, 
be fuppofed to reft on the inclined plane, and to be 
kept from falling down it by a firing C S tyed to its 
center C. Then the force with which this body 
S 2 ilretchei 
