The principle of the instrument was first implemented around 1731 by John Hadley (1682–1744) and Thomas Godfrey (1704–1749), but it was also found later in the unpublished writings of Isaac Newton (1643–1727).

Why was sextant invented?

Those promoting the use of lunar distances, or "lunars," for finding longitude at the end of the 18th century stimulated the invention of the sextant. The sextant was designed to find longitude by measuring the angular distance between the moon and a nearby star.

How did sailors navigate in the 1700s?

The only navigation they had was a sextant, which uses the angle between the sun (or star) and the horizon (constantly bouncing up and down due to strong Antarctic waves) to calculate latitude.