INCLINATION, :MAGNETIC, or DIP. The angle made with the horizontal by the axis of a magnetic needle swinging freely in a vertical plane. The inclination of a magnetic needle varies at different places of the earth's surface, ranging from 90° at the magnetic poles to zero at the magnetic equator. The varying amount of magnetic inclination will be found indicated on the isoclinic charts accompanying the article MAGNETISM, TERRESTRIAL. This property of a magnetic needle was first discovered by Robert Norman in 1576, and an instrument was de vised by him by which the amount could be measured. The phenomenon had previously been noticed by George Hartman, in Nuremberg, in 1544, hut he was neither able to measure the amount of inclination accurately nor to explain the phenomenon. The amount of inclination is determined by the dipping needle (q.v.) and is
measured when the magnetic needle is freely swinging in a vertical plane containing the me ridian. If the plane of the needle is placed at right angles to the magnetic meridian, the axis needle will form an angle of 90° with the hori zontal. The dip of the needle is subject to the same periodic variations as its declination (q.v.), but these changes play a far less important part. In order that an ordinary compass-needle may swing in a horizontal plane, it is customary in northern latitudes to make the southern end of the needle heavier; or the same effect may be secured by using a symmetrical needle which has been weighted with a small bit of brass on its southern half. See COMPASS; DECLINATION; DIP OF TILE MAGNETIC NEEDLE; DIPPING NEEDLE; MAGNETISM; MAGNETISM, TERRESTRIAL.