[ ”5 ] 
they ad in sequilibrio : which is the firft and moft 
iimple cafe of the property of the lever ; for here the 
directions of the weights are fuppofed to be perpen- 
dicular to the line on which they ad, and it is evident 
that, if one of the points C, D or F, be fixed or con- 
fidered as a fulcrum, that the weights ading on the 
other two points will continue to fupport each other. 
I (hall not trouble you with proving the fecond cafe 
of the property of the lever; it is moft eafily deduced 
from the firft: for, when two weights ad on the arms 
of a lever in oblique diredions, and are to each other 
inverfely as the perpendicular diftances of their lines 
of diredion from the center of motion, then, by the 
refolution of forces, it is eafily proved, that the parts 
of thofe forces which ad perpendicularly on the arms 
of the lever, and which only are exerted to turn the 
lever, are to each other inverfely as the lengths of 
thofe arms ; and therefore by the firft cafe they muft 
ballance each other. 
I (hall now mention fome well known truths in 
mechanics, which, I think, cannot be proved otherwife 
than by deducing them from what hath been here 
demonstrated. 
C O R. I. 
It appears from hence, that the powers with which 
any two forces move or endeavour to move the arms 
of a lever, are as the redangles, under lines propor- 
tional to the forces, and the perpendicular diftances of 
their lines of diredion from the fulcrum.- 
