<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2011) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2011) (Learn how and when to remove this template message) </Td> </Tr> <P> Dip circles (also dip needles) are used to measure the angle between the horizon and the Earth's magnetic field (the dip angle). They were used in surveying, mining and prospecting as well as for the demonstration and study of magnetism . </P> <P> 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 around 1576 investigated dip angle further and in 1581 described in print a device to measure this phenomenon . </P>

Determination of angle of dip by dip circle