The classic marine sextant does not have a single, simple “inventor.” Most historians credit the practical invention of the sextant’s principle around 1730–1731 to John Hadley in England and Thomas Godfrey in colonial America, who independently developed very similar double‑reflecting instruments.

Quick Scoop

  • The sextant principle (double reflection for measuring angles) appears in unpublished work by Isaac Newton from the late 1600s, but his design was not built or adopted at the time.
  • Around 1730, Thomas Godfrey in Philadelphia and John Hadley in England each produced working double‑reflecting instruments for navigation; Hadley’s version became the direct ancestor of the modern sextant.
  • The Royal Society in London investigated the priority question and awarded both Hadley and Godfrey monetary recognition for their contributions.
  • In 1757, Captain John Campbell enlarged the earlier octant design to create an instrument covering a sextant of a circle (60° arc measuring up to about 120°), which aligns with what we now recognize as the standard marine sextant.

So, if you need a name for “who invented the sextant” in a short answer, the safest historically grounded answer is:

  • John Hadley is usually credited as the inventor of the modern sextant, with Thomas Godfrey recognized as an independent co‑inventor, and Newton as the earlier conceptual originator whose design surfaced only later.

Information gathered from public forums or data available on the internet and portrayed here.