Dipping-needle

(-ne'dl,) or INCLINATION COMPASS. (Mag.) An instrument for measuring the dip or magnetic inclination at a given place. It consists of a graduated horizontal bra circle, m (Fig. 267), supported on three legs, provided with levelling screws. Above this circle there is a plate, A, movable about a vertical axis, and supporting by means of two columns a second M b d r A m Fig. 267. DIPPING-NEEDLE. graduated circle, M, which measures the inclination. The needle rests on a frame, r, and the diameter pa ing through the two zeros of the circle, M, can be ascertained to be perfectly horizontal by means of the spirit level, n. To observe the inclination, the magnetic meridian must first be determined, which is effected by turning the plate A on the circle m, until the needle is vertical,which is the case when it is in a plane at right angles to the magnetic meridian. The plate A is then turned 90° on the circle m, by which the vertical circle, M, is brought into the magnetic meridian. The angle, dca, which the magnetic needle makes with the horizontal diameter, is the angle of inclination. [s. 289] IMG:p0318_0.jpg:Gravür