Shen Kuo first discovered dip angle in 11th century. He recorded this discovery in his famous book Meng Xi Bi Tan. In western, Georg Hartmann first discovered dip angle in 1544, when he noticed the needle on a compass dipped towards the north hemisphere. Rather than explore this phenomenon, Hartmann sought ways to eliminate it. However, Robert Norman investigated dip angle further and in 1581 described in print a device to measure this phenomenon.
Unfortunately, early dip circles were not accurate and gave poor results. Over the next 300 years many improvements were made most notably the friction between the needle and its pivot was reduced and the circle was encased in glass. Between the late 18th century and late 19th century the design approached its peak and by World War I the most advanced dip circles were being made. With the development of electronic systems dip circles became obsolete and dip angle is rarely measured anymore.
The reversal of the poles of the needle is to counteract any error produced by the centre of gravity of the needle being displaced from the centre of the axle in a direction parallel to the length of the needle.
Attached to the axle of the ring is a divided circle, by means of which and two reading microscopes the inclination of the axis of rotation of the coil to the horizontal can be read.
The commutator being connected to a sensitive galvanometer, the coil is rotated, and the ring adjusted till the galvanometer is undeflected.
Over the N. magnetic pole the north-seeking end of the needle points directly downwards and dips at an intermediate angle at intermediate distances between the magnetic poles and equator.
There are secular progressive variations of dip as well as of declination and the maxima are independent of each other.
In 1576 the dip at London was 71° 50', In 1720 (max.) 74 42', in 1900 67° 9'.
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