to prepare, besides necessitating fresh mixing each time the ink is used.

Protractor. A protractor is a circular scale

Fig. 25 Chinese Stick Black Drawing Ink.

and is divided into degrees and fractions of a degree. Protractors are made both circular and semi-circular in shape, the latter being the ordi

120

E.D-CO

Fig. 26-German Silver Protractor.

be readily applied to the point at which it is desired to read or lay off an angle.

Drawing Boards. A drawing board for ordinary use should be about 20 by 27 inches in size. The material should be of first quality clear soft pine, free from pitch and thoroughly kiln dried. The board should be made of five or six strips about 4 by 27 inches, well glued together and held from warping by two cleats on the back, as shown in Fig. 27.

The working edge of the drawing board should

A line is the boundary or limit of a surface.
A line has only one dimension, that of length.
A point is considered as the extremity or limit

of a line. The place where two lines intersect is also a point. A point has position but no dimen'sions.

In practical work a point is represented by a fine dot.

Lines may be either straight, broken or curved. A straight line is one which has the same direction throughout its length.

A straight line is also called a right line.

A straight line is usually called a line simply, and when the word line occurs it is to be understood as meaning straight line unless otherwise specified. A straight line is the shortest distance between two points. If any other path between the points were chosen, the line would become curved or broken. Therefore two points determine the position of the straight line joining them.

A broken line is one which changes direction at one or more points.

A curved line is one which changes direction

constantly throughout its length. The word curve is used to denote a curved line.

Lines may be represented as full, dotted, dashed, or dot-and-dashed.

A full line is one which is continuous throughout its length.

A dotted line is one which is composed of alternate dots and spaces.

A dash line is one which is composed of alternate dashes and spaces.

A dot-and-dash line is one which is composed of dots, spaces and dashes. These may be arranged in several ways according to the character of the line, that is, the meaning it is to convey. Surfaces may be either plane or curved. plane surface is usually called a plane.

A

A plane is such a surface that if a straight line be applied to it in any direction, the line and the surface will touch each other throughout their length.

A curved surface is one no part of which is a plane.

Any combination of points, lines, surfaces or solids is termed a figure.