lade without moving it, and without
permitting them to move upon it. The learner will find that this is best
attained by so regulating the height of the square-blade that the line
to be drawn does not come down too near the bottom of the triangle or
edge of the square-blade, nor too high on the triangle; that is to say,
too near its uppermost point. It is the left-hand edge of the triangle
that is used, whenever it can be done, to produce the required line.

[Illustration: Fig. 6.]

CURVES.

To draw curves that are not formed of arcs or parts of circles,
templates called curves are provided, examples of these forms being
given in Figure 6. They are made in wood and in hard rubber, the latter
being most durable; their uses are so obvious as to require no
explanation. It may be remarked, however, that the use of curves gives
excellent practice, because they must be adjusted very accurately to
produce good results, and the drawing pen must be held in the same
vertical plane, or the curve drawn will not be true in its outline.

DRAWING INSTRUMENTS.

It is not intended or necessary to enter into an elaborate discussion of
the various kinds of drawing instruments, since the purchaser can obtain
a good set of drawing instruments from a reputable dealer by paying a
proportionate price, and must _per force_ learn to use such as his means
enable him to purchase. It is recommended that the beginner purchase as
good a set of instruments as his means will permit, and that if his
means are limited he purchase less than a full set of instruments,
having the same of good quality.

All the instruments that need be used in the examples of this book are
as follows:

A small spring bow-pen for circles, a lining pen or pen for straight
lines, a small spring bow-pencil for circles, a large bow-pen with a
removable leg to replace by a divider leg or a pencil leg, and having an
extension piece to increase its capacity.

The spring bow-pen should have a stiff spring, and should be opened out
to its full capacity to see that the spring acts well when so opened
out, keeping the legs stiff when opened for the larger diameters. The
purchaser should see that the joint for opening and closing the legs is
an easy but not a loose fit on the screw, and that the legs will not
move sideways. To test this latter, which is of great importance in the
spring bow-pencil as well as in the pen, it is well to close the legs
nearly together and takin