Diagram, 'A new levell' by Chr [Christopher] Wren A diagram of Wren's invention of a new level, accompanied by a caption describing its use. The level is constructed of a concave glass placed on a foot with a ball and socket allowing it to turn. A drop of quicksilver [mercury] can be placed on it to find the any azimuth. Subject: Physics Produced at the Royal Society on 14 March 1667. [1667]