Like all the arts, drawing has a nomenclature of its own, and nothing can be more helpful to the beginner than to know the name of things relating to the art of drawing. This is a language almost peculiar to itself, and used daily and hourly by many thousands of superintendents, foremen and master mechanics, as well as by owners, designers and draughtsmen, hence its introduction at this early stage.

ALTITUDE. This is the elevation of an object above its base, or the perpendicular distance between the top and bottom of a figure.

ANGLE is the difference in the direction of two lines which meet or tend to meet. The lines are called the sides and the point of meeting, the vertex of the lines.

ANGLE.

An angle is commonly designated by a letter at its vertex; but when two or more angles have their vertices at the same point, they cannot be thus distinguished.

For example,

when the three lines

A B, A C,and AD in fig. 37 meet in the common point A, we designate either of the angles formed, by three letters, placing that at the vertex

between those at the opposite extremities of the including lines. Thus, we say, the angle BA C, etc. APEX. The summit or highest point of an object. ARC.-See circle.

AXIS OF A SOLID.-An imaginary straight line passing through its center.

AXIS OF A FIGURE.-A straight line passing through the center of a figure, and dividing it into two equal parts.

BASE. The base of a solid figure is that on which it stands-the lowest part.

BISECT. To divide into two equal parts.

BISECTOR.-A line which bisects.

CIRCLE.

The Radius of a circle is a line extending from its center to any point in the circumference. It is one-half of the diameter. All the diameters of a circle are equal, as are also all the radii CD, CB and C A.

An Arc of a circle is any portion of the circumference, as B D and AD.

Semi-Circle.-Half a circle formed by bisecting it with a diameter, as A C B. Fig. 38.

An angle having its vertex at the center of a circle is measured by the arc intercepted by its sides. Thus, the arc AD measures the angle A CD, and in general, to compare different angles, we have but to compare the arcs, included by their sides, of the equal circles having their centers at the vertices of the angles.

CIRCUMSCRIBE.-To draw a line of figures about or outside, such as a circle drawn around a square touching its corners or angles.

CIRCUMSCRIBE.

Inscribe.-To draw a line or figure inside or on the interior, such as a circle drawn within a square touching its sides.

CONCAVE.-Curving inwardly.

CONE.-A solid body or figure having a circl for its base, and its top terminated in a point or vertex. CONSTRUCTION.-The making of any object. CONTOUR. The outline of the general appearance of an object.

CONVERGENCE.-Lines extending towards a common

CURVE.-A line of which no part is straight.

Reversed Curve.-One whose curvature is first in one direction and then in the opposite direction.

Spiral Curve.-A plain curve which winds about and recedes, according to some law, from its point of beginning, which is called its center. CYLINDER.-A solid bounded by a curved surface and by two opposite faces called bases; the bases may be any curved figures and give the name to the cylinder; thus a circular cylinder is one whose bases are circles.

CYLINDRICAL.-Having the general form of a cylinder. DEGREE.-The 360th part of a circle.

DESCRIBE. To make or draw a curved line; to draw

a plan.

DESIGN. Any arrangement or combination to produce desired results in industry or art. Το delineate a form or figure by drawing the outlinea sketch.

DEVELOP. To unroll or lay out.

DIAGONAL.-A right line drawn from angle to angle of a quadrilateral or many angled figure and dividing it into two parts.

DIAMETER.—A right line passing through the center of a circle or other round figure terminated by the curve and dividing the figure symmetrically into two equal parts.

EDGE. The intersection of any two surfaces. ELEVATION.—The term elevation, vertical projection

and front view-applied to drawings-all have the same meaning.

FACE. One of the plane surfaces of a solid; it may be bounded by straight or curved edges. FINISHING.-Completing a drawing whose lines have been determined by erasing unnecessary lines and strengthening and accentuating where this is

needed.

FORESHORTENING.-Apparent decrease in length, owing to objects being viewed obliquely; thus a wheel, when seen obliquely, instead of appearing round, presents the appearance of an ellipse. FREE-HAND.-Executed by the hand unaided by instruments.

GENERATED.-Produced by.

GEOMETRIC.-According to geometry.

HALF-TINT.-The shading produced by means of parallel equidistant lines.

HEMISPHERE.-Half a sphere obtained by bisecting a sphere by a plane.

HORIZONTAL.-Parallel to the surface of smooth water. In drawing, a line drawn parallel to the top and bottom of the sheet is called horizontal. INSCRIBE.-See circumscribe-its opposite. INSTRUMENTAL.-By the use of instruments.