by broader lines,
which are called shadow or shade lines. These lines will often serve to
indicate the shape of some part of the piece represented, as will be
seen from the following examples. In Figure 97 is a piece that contains
a hole, the fact being shown by the circle being thickened at A. If the
circle were thickened on the other side as at B, in Figure 98, it would
show that it represented a cylindrical stem instead of a hole.

[Illustration: Fig. 97.]

[Illustration: Fig. 98.]

[Illustration: Fig. 99.]

In Figure 99 is represented a washer, the surfaces that are in the
shadow side being shown in a shade line or shadow line, as it is often
called.

In Figure 100 is a key drawn with a shade line, while in Figure 101 the
shade line is shown applied to a nut. The shade line may be produced in
straight lines by drawing the line twice over, and slightly inclining
the pen, or by opening the pen points a little. For circles, however, it
may be produced either by slightly moving the centre from which the
circle is drawn, or by going over the shade part twice, and slightly
pressing the instrument as it moves, so as to gradually spring the legs
farther apart, the latter plan being generally preferable.

[Illustration: Fig. 100.]

[Illustration: Fig. 101.]

[Illustration: Fig. 102.]

Figure 102 shows a German pen, that can be regulated to draw lines of
various breadths. The head of the adjusting screw is made rather larger
than usual, and is divided at the under side into twenty divisional
notches, each alternate notch being marked by a figure on the face. By
this arrangement a uniform thickness of line may be maintained after
filling or clearing the pen, and any desired thickness may be repeated,
without any loss of time in trial of thickness on the paper. A small
spring automatically holds the divided screw-head in any place. With
very little practice the click of the spring in the notches becomes a
sufficient guide for adjustment, without reference to the figures on the
screw-head. Another meritorious feature of this pen is that it is armed
with sapphire points, which retain their sharpness very long, and thus
save the time and labor required to keep ordinary instruments in order
for the performance of fine work.

An example of line shading in perspective drawing is shown in the
drawing of a pipe threading stock and die in Figure 103.

[Illustration: Fig. 103.]

Shading by means of lines may be used with