in dialling, the style, pin, or cock of a dial, which by its shadow shows the hour of the day. The gnomon of every dial represents the axis of the world: (See Dial and Dialling.)—The word is Greek, γνώμων, which literally implies something that makes a thing known; by reafop that the style or pin indicates or makes the hour known.

in astronomy, a style erected perpendicular to the horizon, in order to find the altitude of the sun. Thus, in the right-angled triangle ABC are given, AB the length of the style, BC the length of its shadow, and the right angle ABC. Hence, making CB the radius, we have this analogy for finding the angle ACB, the sun's altitude, viz. BC : AB :: radius : tangent of the angle C.

By means of a gnomon, the sun's meridian altitude, and consequently the latitude of the place, may be found more exactly than with the smaller quadrants. See Quadrant. By the same instrument the height of any object GH may be found: for as DF, the distance of the observer's eye from the gnomon, is to DE, the height of the style; so is FH, the distance of the observer's eye from the object, to GH, its height.

See further on the uses and application of Gnomons, the article Geography, no. 49—53.

GNOMON of a Globe; the index of the hour-circle.