Davis Quadrant

The Davis quadrant, or backstaff, was invented by the English navigator John Davis around 1594 and described in his 1595 book The Seamans Secrets. The observer stood with the sun behind, casting a shadow from a vane onto a horizon vane while sighting the horizon, so the navigator never looked into the sun, the chief flaw of the cross-staff. It dominated latitude observation through the seventeenth and into the eighteenth century until Hadley’s reflecting octant and the sextant replaced it. Davis also explored the strait between Greenland and Baffin Island that bears his name.