A rare John Dobson backstaff or Davis quadrant, English, dated 1730, signed on ivory plaque MADE BY JOHN DOBSON 1730 FOR MR THOMAS SALKELD, with lignum vitae frame, boxwood arcs and replaced vanes, the 30 degree transversal scale with fleur de lys stamped decoration, the back with scales for the Sun's declination and the right ascension, 22 in (56cm) long,
This elegant compendium—an astronomical toolkit from 1557—contains two different kinds of sundial, a nocturnal and two lunar volvelles to tell time at night, a world map, ten pages engraved with astronomical and astrological tables, seven blank pages, and a magnetic compass. (Adler Collections M-363)
Josuah Habermel (attr.) (16th century) Quadrant, after 1582 Florence, Istituto e Museo di Storia della Scienza, inv. 2518 A small instrument with a double graduation on the edge for measuring heights and distances. On the back is a table for computing Easter according to the Gregorian calendar.