ANGLE, the point where two lines meet, or the meeting of two lines in a point. Technically, the inclination of two lines to one another. Angles may be ranked under two leading divisions, plane and solid angles. A plane angle is the inclination of two lines to one an other in a plane, which two lines meet together. A solid angle is that which is made by the meeting in one point of more than two plane angles, which, how ever, are not in the same plane. Each of the leading divisions, plane and solid angles, may again be subdivided into rectilineal, curvilineal, and mixed angles. A plane rectilineal angle is the inclina tion to each other of two straight lines, which meet together, but are not in the same straight line. A curvilineal angle is the inclination to each other of two curved lines which meet in a point. A mixed angle is one formed by the meet ing of a curve and a straight line.
Angles are measured by arcs, and it is immaterial with what radius the latter are described. The result is generally stated in degrees, minutes, and seconds. The point at which the lines forming the angle meet is called the angular point or the vertex of the angle, and the lines themselves the sides or legs of the angle.
Plane rectilineal angles are generally divided into right and oblique, or into right, obtuse, and acute. When a straight line standing upon another straight line makes the two adjacent angles (those on the right and left of it) equal to one another, each of them is called a right angle. An oblique angle is one which is not a right angle. An obtuse angle is that which is greater than one right angle, but less than two. An acute angle is that which is less than a right angle: both are oblique. A spherical angle is one formed by the in tersection or the meeting of two great circles of a sphere.
In mechanics, there are angles of di rection, of friction, of repose, etc.
Optics has angles of incidence, of re flection, of refraction, of deviation, of polarization, etc.
Astronomy has angles of position, of situation, of elevation, inclination, de pression, etc.