Wooden horary quadrant, Arabian, 1730-31.
© Science Museum / Science & Society Picture Library
This Islamic horary quadrant was made by Mustafa Ayyubi in the Middle East. Made of wood, the quadrant has hand drawn painted scales and inscriptions. Horary is an archaic term meaning 'of or relating to hours'. The horary quadrant was 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 tread of the plumb bob of the instrument. The horary quadrant was derived from the astrolabe and first appeared during Medieval times. Like its predecesor, it includes a two-dimensional depiction of a celestial sphere that is reduced to a quarter.