Discover

'Dip circles' are used to measure the angle between the horizon and the Earth's magnetic field (the dip angle). They were used in navigation, mining and prospecting as well as for the demonstration and study of magnetism.
Shen Kuo first discovered dip angle in 11th century. He recorded this discovery in his famous book ''Dream Pool Essays'' (''Meng Xi Bi Tan''). In the west, 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.