Bras horary quadrant, 1549.
© Science Museum / Science & Society Picture Library
This electrotype copy of rectangular horary quadrant was made by Georg Hartmann (1489-1564) in Nuremberg, Germany. Horary quadrants were used for finding local time by sighting either the Sun or a bright star at night. Held vertically, a measurement could be taken from the position on the scale of a moveable bead on the thread of the instrument's plumb bob. The instrument was derived from the astrolabe and first appeared during Medieval times. Like its predecesor, it includes a two-dimensional depiction of the heavens that is reduced to a quarter. This reverse view shows extra timekeeping scales.