excellent effect in
mechanical drawing, not only to distinguish round from flat surfaces,
but also to denote to the eye the relative distances of surfaces. Figure
104 represents a cylindrical pin line shaded. As the light is supposed
to come in from the upper left-hand corner, it will evidently fall more
upon the left-hand half of the stem, and of the collar or bead, hence
those parts are shaded with lighter or finer lines than the right-hand
sides are.

[Illustration: Fig. 104.]

[Illustration: Fig. 105.]

Two cylindrical pieces that join each other may be line shaded at
whatever angle they may join. Figure 105 represents two such pieces, one
at a right angle to the other, both being of equal diameter.

[Illustration: Fig. 106.]

Figure 106 represents a drawing of a lathe centre shaded by lines, the
lines on the taper parts meeting those on the parallel part A, and
becoming more nearly parallel to the axis of the piece as the centre of
the piece is approached. The same is the case where a piece having a
curved outline is drawn, which is shown in Figure 107, where the set of
the bow-pen is gradually increased for drawing the shade lines of the
curves. The centres of the shade curves fall in each case upon a line at
a right angle to the axis of the piece, as upon the lines A, B, C, the
dotted lines showing the radius for each curve.

[Illustration: Fig. 107.]

The lines are made finer by closing the pen points by means of the screw
provided for that purpose. The pen requires for this purpose to be
cleaned of the ink that is apt to dry in it.

In Figure 108 line shading is shown applied to a ball or sphere, while
in Figure 109 it is shown applied to a pin in a socket which is shown in
section. By showing the hollow in connection with the round piece, the
difference between the two is quite clearly seen, the light falling
most upon the upper half of the pin and the lower half of the hole. This
perhaps is more clearly shown in the piece of tube in Figure 110, where
the thickness of the tube showing is a great aid to the eye. So,
likewise, the hollow or hole is more clearly seen where the piece is
shown in section, as in Figure 111, which is the case even though the
piece be taper as in the figure. If the body be bell-mouthed, as in
Figure 112, the hollow curve is readily shown by the shading; but to
line shade a hollow curve without any of these aids to the eye, as say,
to show a half of a tin tube, is a very dif