stem, and therefore represent their
diameters while showing that both are round. A straight line is in
geometry termed a right line.

A line at a right angle to another is said to be perpendicular to it;
thus, in Figures 39, 40, and 41, lines A are in each case perpendicular
to line B, or line B is in each case perpendicular to line A.

A point is a position or location supposed to have no size, and in cases
where necessary is indicated by a dot.

[Illustration: Fig. 41.]

[Illustration: Fig. 42.]

[Illustration: Fig. 43.]

Parallel lines are those equidistant one from the other throughout their
length, as in Figure 42. Lines maybe parallel though not straight; thus,
in Figure 43, the lines are parallel.

[Illustration: Fig. 44.]

[Illustration: Fig. 45.]

[Illustration: Fig. 46.]

A line is said to be _produced_ when it is extended beyond its natural
limits: thus, in Figure 44, lines A and B are _produced_ in the point C.

A line is bisected when the centre of its length is marked: thus, line A
in Figure 45 is bisected, at or in, as it is termed, _e_.

The line bounding a circle is termed its circumference or periphery and
sometimes the perimeter.

A part of this circumference is termed an arc of a circle or an arc;
thus Figure 46 represents an arc. When this arc has breadth it is termed
a segment; thus Figures 47 and 48 are segments of a circle. A straight
line cutting off an arc is termed the chord of the arc; thus, in Figure
48, line A is the chord of the arc.

[Illustration: Fig. 47.]

[Illustration: Fig. 48.]

[Illustration: Fig. 49.]

[Illustration: Fig. 50.]

[Illustration: Fig. 51.]

A quadrant of a circle is one quarter of the same, being bounded on two
of its sides by two radial lines, as in Figure 49.

When the area of a circle that is enclosed within two radial lines is
either less or more than one quarter of the whole area of the circle the
figure is termed a sector; thus, in Figure 50, A and B are both sectors
of a circle.

A straight line touching the perimeter of a circle is said to be tangent
to that circle, and the point at which it touches is that to which it is
tangent; thus, in Figure 51, line A is tangent to the circle at point B.
The half of a circle is termed a semicircle; thus, in Figure 52, A B and
C are each a semicircle.

[Illustration: Fig. 52.]

[Illustration: Fig. 53.]

The point from which a circle or arc of a circle is drawn is termed its
centre. The l