AN OTTOMAN DAIRAT AL-MUADDIL

The dairat al-mu’addil (Eng. equatorial circle) is an instrument with combines a sundial with a qibla indicator. It was invented by the 15th century astronomer and timekeeper at the al-Mu’ayyad mosque in Cairo, ‘Abd al-Aziz ibn Muhammad al-Wafa’i al-Miqati. It was later also described by other scholars, including the Turkish admiral Seydi Ali Reis, making the instrument very popular in Ottoman circles.

The main disk of the instrument consists of a circular brass plate. The center of a disk features a magnetic compass. Around the magnetic compass is a wind-rose with the typical four quarters of the compass: shimal (north), junub (south), sharq (west), garb (east)], and in between alternatingly in Ottoman Turkish “orta” (intermediary winds) and “kerte” (rhumb lines). Around the circumference are marked the names and Qiblas of various localities.

The instrument also features a small sundial below the south point of the instrument equipped with a small gnomon. The various holes on the instrument are due to the missing parts such as four leveling screws and a graduated semi-circular arc which is hinged along the east-west line of the instrument. This arc can be inclined at any desired angle to the horizontal plane by means of the graduated scale in the plane of the meridian.