Circle

(sür'kl.) [Fr. cercle, from L. circulus, round. ] (Geom.) A plane figure bounded by a curved line, which is called its circumference, and is everywhere equally distant from a point within, called its centre; also, the circumference or periphery itself. A circle is described with a pair of compa es, by fixing one foot in the centre and turning the other round to trace out the curved line. The circumference of every C. is supposed to be divided into 360 equal parts, which are called degrees, and are marked; each degree into 60 minutes, marked '; and each minute into 60 seconds, marked ".-The rectification of the C., or the determination of the ratio of the circumference of the diameter, is a problem which has exercised ignorance in all ages. In a rough way, the diameter may be considered as one-third of the circumference. But more accurately, and in ordinary measurements, it may be a umed to have the ratio of 113 to 355; that is,to find the circumference, multiply the diameter by 355, and divide the result by 113. The areas of C. are as the squares of their diameters. Thus the areas of 2 circles, one 2 feet in diameter, and the other 3, are as 4 is to 9; 4 and 9 being the squares of 2 and 3.- (Astron. and Geog.) See DECLINATION, ECLIPTIC, EQUATOR, LATITUDE, SPHERE, . [s. 190]