he
_weight_ and the _power_ are equal.

[Illustration: _Fig. 126. Simple Lever_]

THE LEVER PRINCIPLE.--Now, without stopping to inquire, the boy will
say: "Certainly, I can understand that. As the lever is four times
longer on one side of the fulcrum than on the other side, it requires
only one-fourth of the weight to balance the four pounds. But suppose I
push down the lever, at the point where the weight (D) is, then, for
every pound I push down I can raise four pounds at C. In that case do I
not produce four times the power?"

I answer, yes. But while I produce that power I am losing something
which is equal to the power gained. What is that?

[Illustration: _Fig. 127. Lever Action_]

First: Look at Fig. 127; the distance traveled. The long end of the
lever is at its highest point, which is A; and the short end of the
lever is at its lowest point C. When the long end of the lever is pushed
down, so it is at B, it moves four times farther than the short end
moves upwardly, as the distance from C to D is just one-fourth that from
A to B. The energy expended in moving four times the distance balances
the power gained.

POWER VS. DISTANCE TRAVELED.--From this the following law is deduced:
That whatever is gained in power is lost in the distance traveled.

Second: Using the same figure, supposing it was necessary to raise the
short end of the lever, from C to D, in one second of time. In that case
the hand pressing down the long end of the lever, would go from A to B
in one second of time; or it would go four times as far as the short
end, in the same time.

POWER VS. LOSS IN TIME.--This means another law: That what is gained in
power is lost in time.

Distinguish clearly between these two motions. In the first case the
long end of the lever is moved down from A to B in four seconds, and it
had to travel four times the distance that the short end moves in going
from C to D.

In the second case the long end is moved down, from A to B, in one
second of time, and it had to go that distance in one-fourth of the
time, so that four times as much energy was expended in the same time to
raise the short end from C to D.

WRONGLY DIRECTED ENERGY.--More men have gone astray on the simple
question of the power of the lever than on any other subject in
mechanics. The writer has known instances where men knew the principles
involved in the lever, who would still insist on trying to work out
mechanical devices in which p