or DAVIS'S QUADRANT, an instrument invented by Captain John Davis, about the year 1590, for taking the sun's altitude at sea; but now superseded by Hadley's quadrant. It consisted of two concentric arcs and three vanes, the arc of the longer radius being 30 degrees, and that of the shorter 60 degrees, thus making altogether 90 degrees, or a quadrant. It derived its name from the observer's standing with his back to the sun.