efore noted, the wood must
be soft pine, well seasoned and free from knots, while the battens B
should be dovetailed in and the face of the board trued after they are
glued and driven in. To true the edges square, it is best to make the
two longest edges parallel and straight, and then the ends may be
squared from those long edges.

[Illustration: Fig. 1.]

THE $T$ SQUARE.

Drawing squares or T squares, as they are termed, are made of wood, of
hard rubber and of steel.

There are several kinds of T squares; in one the blade is solid, as it
is shown in Figure 5 on page 20; in another the back of the square is
pivoted, so that the blade can be set to draw lines at an angle as well
as across the board, which is often very convenient, although this
double back prevents the triangles, when used in some positions, from
coming close enough to the left hand side of the board. In an improved
form of steel square, with pivoted blade, shown in Figure 2, the back is
provided with a half circle divided into the degrees of a circle, so
that the blade can be set to any required degree of angle at once.

[Illustration: Fig. 2.]

[Illustration: Fig. 3.]

[Illustration: Fig. 4.]

THE TRIANGLES.

[Illustration: Fig. 5.]

Two triangles are all that are absolutely necessary for a beginner. The
first is that shown in Figure 3, which is called a triangle of 45
degrees, because its edge A is at that angle to edges B and C. That in
Figure 4 is called a triangle of 60 degrees, its edge A being at 60
degrees to B, and at 30 degrees to C. The edges P and C are at a right
angle or an angle of 90 degrees in both figures; hence they are in this
respect alike. By means of these triangles alone, a great many straight
line drawings may be made with ease without the use of a drawing square;
but it is better for the beginner to use the square at first. The manner
of using these triangles with the square is shown in Figure 5, in which
the triangle, Figure 3, is shown in three positions marked D E F, and
that shown in Figure 4 is shown in three positions, marked respectively
G H and I. It is obvious, however, that by turning I over, end for end,
another position is attained. The usefulness in these particular
triangles is because in the various positions shown they are capable of
use for drawing a very large proportion of the lines that occur in
mechanical drawing. The principal requirement in their use is to hold
them firmly to the square-b