Relation of the Laws of Mechanics to Perpetual Motion. 181 
from which it has descended. There is, therefore, no force at all 
derived from the weight, except during the period ‘of a single de- 
scent, and that only equal to the power which hed been mae 
to raise it up to the point of starting. It willbe. said, perha 
that the weight may be made to restore itself, that. it may acquire 
a velocity in falling, sufficient to raise it to the same height again. 
So it may. The ball of a pendulum may raise itself to the sa 
point from which it started, or nearly so. But it can do nothing 
more. ‘The force acquired i in the descent will be all expended 
in the ascent. There will be nothing left to be applied toany =~ 
machinery. , 
There is no avoiding of this result, unless some way can be 
contrived to make the body either acquire a greater force by fal- 
ling, or expend less in rising. No met as yet been devised, 
to bring a body to the ground by its weight, with a greater foree 
than that which it acquires by falling perpendicularly. It m 
be made to roll down an inclined plane, to descend ‘on the are ‘of y apa. 
a circle, on the arm of a lever, or along a series of lines differ-,. 
ently inclined to the horizon. But in every such:case, though it ta 
1s easy to diminish the force of the descent; yet there isno way», 
of increasing it, but by the application of a foreign impulse. | 
the other hand, a body can, by no 
Bo ur, 
t may not advantage be taken of some of the meghanical 
powers, to effect the object with more economy of force, ae 
pose. the weight be made to descend on the longer ; arm-of a | 
_“*-and'to ascend on the shorter arm. If one be twice | as long as t 
ae Bay te not one meee raise seal A Ba pounds ? t_may? 
Bat it i es itself, 
Pes 
will raise y half 4s faras 
