Sextant (later comparison)
A later comparison: neither the octant nor the sextant existed in the Golden Age of Piracy (c.1650–1725). John Hadley's reflecting octant reached the Royal Society in 1731 and John Campbell's sextant followed around 1757 — a generation after the last of the great pirate crews were hanged. The instrument is shown here for what it replaced: the cross-staff, the backstaff (Davis quadrant) and the mariner's astrolabe in the cases beside it, which are what a pirate navigator actually held. Its double-reflection principle let an observer bring sun or star down to the horizon in one steady image and read an angle to the minute — the precision the earlier instruments never had, and the reason latitude became routine and, with the chronometer, longitude became possible.