Dip circle

However, Robert Norman around 1576 investigated dip angle further and in 1581 described in print a device to measure this phenomenon.

[1] Early dip circles were not accurate and gave poor results.

Over the next 300 years many improvements were made, including reducing the friction between the needle and its pivot and encasing the circle in glass.

Improvements which made the dip circle a practical aid for polar navigation were made by Robert Were Fox FRS, who developed in the 1830s the first dip circle that could be used on board a moving ship.

Another important improvement to the instrument was developed in the 1830s by the Dublin physicist Humphrey Lloyd, who devised a way of attaching a magnetic needle at right-angles to the dip needle in order to measure the intensity of force (by seeing the extent to which the right-angle needle deflected the dip-needle).