9. The _Versed Sine_ of an arc is the distance from the extremity of the
arc to the foot of the sine.
For the sake of brevity, these technical terms are contracted thus: for
sine _A B_, we write _sin. A B_; for cosine _A B_, we write _cos. A B_;
for tangent _A B_, we write _tan. A B_, etc.
[Illustration: INSTRUMENTS AND MATERIALS]
[Illustration: Fig. 137.]
Drawing Materials and Instruments.
Drawing tools or instruments are contrived solely for mechanical
drawing; aside from this use they are perfectly worthless, hence the
quality of these special utensils is a matter of the first consideration
to the earnest student.
There are several degrees of excellence to be found in the make-up of
drawing instruments and materials; it may be remarked with truth that
“any kind are good enough, and the best none too good,” i. e., a learner
in this delightful art should not stop at the lack of goodness or the
low grade existing in his “tools,” but rather do the best work possible
with the means at hand.
However, in order that acceptable work may be accomplished, fairly good
instruments should be procured. The advice of some one experienced in
the use and care of draughting tools should be sought before purchasing.
A drawing board, a single sheet of paper and a pencil is the simplest
“outfit” to be thought of; to this small beginning may be added, soon
afterwards, an inexpensive pair of compasses, a T-square and a couple of
triangles; a vast range of work can be executed with these few tools.
Nothing else will be needed to do fine work except, perhaps, one or two
pairs of better compasses and a few sweeps or means of drawing irregular
curves; all these had best be purchased separately; for in buying a “box
of instruments,” it may contain some articles which are not desired, or
that are of a wrong size, or even duplicates of those already possessed.
[Illustration: Fig. 138.]
An outfit recommended by the author of “Reed’s Hand Book” is as follows.
Large compasses with movable leg.
A pair of dividers.
Bow pencil.
Bow pen.
Pencil leg for large compasses.
Pen leg for large compasses.
Drawing pen.
Louis Rouillon, B. S., Instructor of Drawing in Pratt Institute, New
York, recommends the following:
Compasses, 5¹⁄₂ inches, with needle point; pen pencil and lengthening
bar.
Drawing pen, 4¹⁄₂ inches.
T-square, 24-inch blade.
45-degree triangle, 9 inches.