Transport & space · 1757

Sextant

A mirrored instrument measures star angles to a fraction of a degree from a moving deck.

Building on John Hadley's 1731 reflecting octant, John Campbell enlarged the arc in 1757 to create the sextant. Double reflection lets a navigator align a star with the horizon on a rolling ship. Paired with the chronometer, it made position fixing reliable for two centuries.

See it in the living tree Wikipedia

Arcs above join it to what it stood on, arcs below to what it led to. The bar places this stretch on the tree's whole timeline.

What it built on 2

Telescope 1608
Mariner's astrolabe 1481

Related measurements

The dashed line marks when it first worked.

Transatlantic crossing time Latest: 3.5 hours (1976) Source: Wikipedia: Transatlantic crossing, duration list; Geography of Transport Systems: liner transatlantic crossing times

World trade as a share of GDP since 1500 Latest: 1950-now (PWT): 57.8 % of GDP (2023) Source: Our World in Data