CIRCUMFERENCE

, in a general sense denotes the line or lines bounding any figure. But it is commonly used in a more limited sense, to denote the curve line which bounds a circle, and which is otherwise called the periphery; the boundary of a right-lined figure being expressed by the term perimeter.

The circumference of a circle is every where equidistant from the centre. And the circumferences of different circles are to one another as their radii or diameters, or the ratio of the diameter to the circumference is a constant ratio, in every circle, which is nearly as 7 to 22, as it was found by Archimedes, or, more nearly, as 1 to 3.1416. Under the article Circle may be seen various other approximations to that ratio, one of which is carried to 128 places of figures, viz by M. De Lagny.

The Circumference of every circle is supposed to be divided into 360 equal parts, called degrees.—Any part of a circumference is called an arc or arch; and a right line drawn from one end of an arc to the other, is called its chord.—The angle at the circumference is equal to half the angle at the centre, standing on the same arc; and therefore it is measured by the half of that arc.