From around 1730, sextants, with an arc of 60°, began to replace old octants as instruments of navigation. They were used to measure the height of a celestial body above the horizon, primarily to determine latitude.
This sextant was manufactured by the noted optician Mercier, and was found in the island of Vanikoro (Solomon Islands) in the wreck of La Boussole, the ship commanded by Monsieur de la Pérouse. It was through this discovery that the wreck was unambiguously identified, as it was listed with the Admiralty as part of the ship's equipment.