Wooden horary quadrant, Persian, 1727-1728.
© Science Museum / Science & Society Picture Library
This Islamic horary quadrant was made by Muhammad Abd al-Hadi-Safadi in Persia (part of modern day Iran). Made of wood, it has hand-drawn painted scales and inscriptions as well as a magnetic compas. 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 thread 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.