[ I2 4 ] 
Wretches the firing will be to its whole weight, as the 
fine of A B D, the angle of elevation, to the fine of the 
angle which the firing contains with a line perpendicu- 
lar to A B the length of the plane. For let the radius 
C E be drawn perpendicular to the horizon, and C F 
perpendicular to AB: and from E draw EO par- 
allel to the firing and meeting C F in O. Then, as the 
body continues at reft and is urged by three forces, to 
wit, by its weight in the direction C E, by the reaction 
of the plane in the direction F C, and by the reaction 
of the firing in the direction E O ; the reaction of the 
firing, or the force by which it is ftretched, is to the 
weight of the body, as E O to C E : that is, as the 
fine of (the angle C E F, which is equal to) A B D, 
the angle of elevation, to the fine of the angle E O C, 
equal to S C O, the angle which the firing contains 
with the line C F perpendicular to A B, the length 
of the plane. 
When therefore the firing is parallel to the length 
of the plane, the force with which it is ftretched, or 
with which the body tends down the inclined plane, is 
to its whole weight, as the fine of the angle of ele- 
vation, to the radius, or as the height of the plane 
to the length. And in the fame manner it may be 
fhewn that, when the firing is parallel to B D, the 
bafe of the plane, the force with which it is ftretched 
is to the weight of the body, as A D to B D, that is, 
as the height of plane to its bafe. If we fuppofe the 
firing, which fupports the body G E F, to be faftened 
at S, and that a force, by adting on the line A D, the 
height of the plane, in a direction parallel to the bafe 
B D, drives the inclined plane under the body, and by 
that means makes it rife in a direction parallel to A I>. 
