Azimuth compass

Azimuth compasses were important in the period before development of the reliable chronometers needed to determine a vessel's exact position from astronomical observations.

[9] Early navigators in the northern hemisphere could calculate latitude relatively easily when the night sky was clear by observing the elevation of Polaris, a star that is very close to the north celestial pole.

In 1588 King Philip II of Spain (1556–1598) offered a large reward to anyone who could find a practical solution to determining longitude.

[10] A novel approach, apparently originating with the Jesuit missionary Christoforo Borri, was to create charts that mapped points of equal magnetic declination.

Walter Hayes, Richard Glynne and Benjamin Ayres (died c. 1775) made accurate large azimuth compasses.

[14] He supplied an azimuth compass designed by Gowin Knight to Joseph Banks for the voyage of HMS Resolution commanded by Captain James Cook in 1772.

[16] On 6 February 1808 the American sealer Topaz, commanded by Captain Mayhew Folger, arrived at Pitcairn Island to take on fresh water.

18th-century azimuthal compass held in the National Archaeological Museum of Spain
The azimuth is the angle formed between a reference direction (North) and a line from the observer to a point of interest projected on the same plane as the reference direction
A map showing lines of equal magnetic declination in late 2024
An example of an azimuth compass. The visors of unequal height allow sighting of objects above the horizon.