al-Munḥarifāt

This 19th-century manuscript is a treatise on gnomonics, the mathematical discipline concerning the calculation of the projection of shadows for timekeeping purposes. The relatively recent date of the work attests to the great and lasting importance attributed in the Islamic world to the reckoning of time through the observation of shadow lengths. The use of gnomonics and the construction of sundials were perceived as the most religiously correct way to calculate the right times of prayers, since religious texts already define the midday (zuhr) and afternoon ('asr) prayers in terms of shadow lengths. This treatise is devoted to one particular kind of sundial only, the munharifa (literally "inclined") or vertical sundial, but Islamic tradition records a vast number of treatises that also describe the so-called horizontal sundial (known as ruhāma or basīta). The tradition of treatises about sundials began in the ninth century with the set of tables for the production of sundials created by the famous mathematician and astronomer Muḥammad ibn Musá al-Khuwarizmi (active 813-46). The work presented here begins with a general description of the shape and features of vertical sundials, which is followed by tables for the appropriate construction and positioning of sundials. The tables are outlined in black and red ink and can be seen on some of the early folios. In some cases these tables occupy a complete manuscript page. World Digital Library.