Sextant And Case (England), ca. 1865

This object is not part of the Cooper Hewitt's permanent collection. It was able to spend time at the museum on loan from National Museum of American History as part of Tools: Extending Our Reach.

Out of sight of land, early sea navigators relied solely on their compass, the sky, and a rough speed measurement to find the way. Though many tools were developed to measure latitude, it was the invention of the sextant in the mid-eighteenth century that navigators could finally accurately determine longitude, the east–west component of position. The device measured lunar distance, the angle between the moon and the sun, or a selected star, which was then checked against a printed table of distances and the times visible at a given location. Comparing with the ship’s local time, the navigator made a precise calculation of position using a series of complicated mathematical corrections. The sextant employs a double reflection technique: using two small mirrors, one on a movable arm, two objects can be examined at the same time. The angle between the "touching" reflections is then determined by reading the position of the arm on a curved, graduated scale. The sextant was the most complicated and expensive navigation instrument of its time, requiring navigators to purchase ancillary tools, including astronomical tables and charts, and to learn to use them. Though eventually supplanted by other navigational instruments, including today’s GPS, sextants are still carried on many ships as a backup for emergencies and as a symbol of the mariner’s skill.

This object was previously on display as a part of the exhibition Tools: Extending Our Reach.