Then draw a
vertical line (A) midway between the marks of the line 2, and this will
be the center of the main pinion.

Also draw a horizontal line (B) midway between the marks on the vertical
line (1), and this will represent the center of the small gear. These
two cross lines (A, B) constitute the intersecting axes of the two
wheels, and a line (5), drawn from the mark (3 to 4), and another line
(6), from the axes to the intersecting points of the lines (1, 2), will
give the pitch line angles of the two wheels.

SPROCKET WHEELS.--For sprocket wheels the pitch line passes centrally
through the rollers (A) of the chain, as shown in Fig. 125, and the
pitch of the chain is that distance between the centers of two adjacent
rollers. In this case the cut of the teeth is determined by the chain.

CHAPTER XI

MECHANICAL POWERS

THE LEVER.--The lever is the most wonderful mechanical element in the
world. The expression, _lever_, is not employed in the sense of a stick
or a bar which is used against a fulcrum to lift or push something with,
but as the type of numerous devices which employ the same principle.

Some of these devices are, the wedge, the screw, the pulley and the
inclined plane. In some form or other, one or more of these are used in
every piece of mechanism in the world.

Because the lever enables the user to raise or move an object hundreds
of times heavier than is possible without it, has led thousands of
people to misunderstand its meaning, because it has the appearance, to
the ignorant, of being able to manufacture power.

WRONG INFERENCES FROM USE OF LEVER.--This lack of knowledge of first
principles, has bred and is now breeding, so-called perpetual motion
inventors (?) all over the civilized world. It is surprising how many
men, to say nothing of boys, actually believe that power can be made
without the expenditure of something which equalizes it.

The boy should not be led astray in this particular, and I shall try to
make the matter plain by using the simple lever to illustrate the fact
that whenever power is exerted some form of energy is expended.

In Fig. 126 is a lever (A), resting on a fulcrum (B), the fulcrum being
so placed that the lever is four times longer on one side than on the
other. A weight (C) of 4 pounds is placed on the short end, and a
1-pound weight (D), called the _power_, on the short end. It will thus
be seen that the lever is balanced by the two weights, or that t