# Encyclopædia Britannica, Ninth Edition/Angle

**ANGLE**, a term employed in different senses, the most
common and simplest use of
it to which all the rest may
be referred, and by which they
may be explained being to
indicate the inclination of two
straight lines to each other. A
Suppose O F in the figure to
turn about O from the posi
tion O B towards O C, like the
opening out of the legs of a pair
of compasses, the angle formed
by O B and O F, which is dis

An image should appear at this position in the text.If you are able to provide it, see Wikisource:Image guidelines and Help:Adding images for guidance. |

of the turning or opening, being of course entirely inde pendent of the length of the lines. The ordinary method of measuring angles is based on the division of the circum ference of a circle into 360 equal parts, called degrees, the angles formed by lines radiating from the centre being proportional to the arcs of the circumference which the lines intercept. If O C makes equal angles with the straight line A O B, each of them is a right angle, or an angle of 90. In the figure A O E is an angle of 60, and C F and F O B are each 45 ; whence E O F is 75, E B 120, &c. By the angle curved lines make with each other is meant the rectilineal angle contained by the tangents to the curves. See Geometry and Trigonometry.