GNOMON

GNOMON, in geometry. If, in a parallelogram ABCD (Pl. CXL. fig. 8. n^o 1.) the diameter AC be drawn; also two lines EF, HI, parallel to the sides of the parallelogram, and cutting the diameter in one and the same point G, so that the parallelogram is, by these parallels, divided into four parallelograms; then are the two parallelograms DG, BG, through which the diameter does not pass, called complements; those through which the diameters pass, E H, F I,

are called the parallelograms about the diameter; and a gnomon consists of the two complements, and either of the parallelograms about the diameter, viz. GD+HE+FI, or GD+FI+GB.