not the
extreme lines at the bottom and at the right side, because of the close
parallel lines.

In Figs. 109 and 110 the blades superposed on the other are very thin,
and the result is the lines at the right side and bottom are made much
heavier.

[Illustration: _Fig. 107. Fig. 108. Illustrating Heavy Lines_]

This is more fully shown in Figs. 107 and 108. Notice the marked
difference between the two figures, both of which show the same set of
pulleys, and the last figure, by merely having the lower and the
right-hand lines of each pulley heavy, changes the character of the
representation, and tells much more clearly what the draughtsman sought
to convey.

SCALE DRAWINGS.--All drawings are made to a scale where the article is
large and cannot be indicated the exact size, using parts of an inch to
represent inches; and parts of a foot to represent feet.

In order to reduce a drawing where a foot is the unit, it is always best
to use one-and-a-half inches, or twelve-eighths of an inch, as the
basis. In this way each eighth of an inch represents an inch. If the
drawing should be made larger, then use three inches, and in that way
each inch would be one-quarter of an inch.

[Illustration: _Fig. 109. Fig. 110. Lines on Plain Surfaces_]

The drawing should then have marked, in some conspicuous place, the
scale, like the following: "Scale, 1-1/2" = 1'"; or, "Scale 3" = 1'."

DEGREE, AND WHAT IT MEANS.--A degree is not a measurement. The word is
used to designate an interval, a position, or an angle. Every circle has
360 degrees, and when a certain degree is mentioned, it means a certain
angle from what is called a _base line_.

[Illustration: _Fig. 111. Illustrating Degrees_]

Look at Fig. 111. This has a vertical line A, and a horizontal line B.
The circle is thus divided into four parts, and where these lines A, B,
cross the circle are the cardinal points. Each of the four parts is
called a quadrant, and each quadrant has 90 degrees.

Any line, like C, which is halfway between A and B, is 45 degrees.
Halfway between A and C, or between B and C, like the line D, is 22-1/2
degrees.

MEMORIZING ANGLES.--It is well to try and remember these lines by fixing
the angles in the memory. A good plan is to divide any of the quadrants
into thirds, as shown by the points E, F, and then remember that E is 30
degrees from the horizontal line B, and that F is 60 degrees. Or, you
might say that F is 30 degrees from the vertic