The hydraulic clock of the al-Bū‘Ināniya madrasah

Like many civilizations, Muslim society took great interest in the orientation and measurement of time and its representation in astronomical cycles. This was a natural response to man’s quest to find his place in time and space. Muslim scientists invented various instruments for regulating the exact times for ritual prayer. Historical texts attest to a number of devices, but only in Fez can an example be seen: the monumental clock opposite the al-Bū ‘Ināniya madrasah, is a technical and artistic masterpiece. Al-Jaznā’ī, in around 1366 described a clock with a series of yellow copper bowls. Every hour, when a weight dropped into one of the bowls, a door would open.

The clock’s facade, which overlooks the thoroughfare, was composed of thirteen bowls fixed onto carved cedar brackets on a facing of beams adorned with an epigraphic decoration of the same style as that found in the madrasah’s courtyard. On top of them was a series of twelve windows. Each bowl received a metal weight that descended at the end of a rope, passing through holes pierced in the brackets supporting the bowls. The rope bearing the weight was moved by the technical device behind it, of which, unfortunately, there remains no trace. This mechanism used the principle of a floater to maintain a regular flow of water, and the water’s descent into the recipient created a proportional movement. Yet, the flow needed to vary with the ‘equal’ and ‘unequal’ hours. If this clock’s hours were not equal, which is very likely, the flow speed must have varied with the length of the days, and hence the twelve intervals recorded daily from sunrise to sunset also varied. This would indicate that the clock’s mechanism had a regulator that controlled the water debit rate.

Because little remains of this mechanism, it could be reasoned that this instrument was fitted with the same regulator (adapted) as that described by the scientist, al-Jazarī (twelfth century), for one of his clocks, as can be seen in a painting dating from 1315[1]. Vitruvius had already given a vague description of the idea behind this system of regulation. It involves a technical design that ensures the regulation of the size of the orifice for the water flow in accordance with the sun’s position in the zodiac signs. The correct working of this mechanism, using a pulley system, freed the weight whilst opening the windows.

Despite knowledge about the two systems of time measurement, it would seem that it was common practice to count the hours unequally, although this method was more complex. In reality, this technical choice was better suited to the vision and use of time in the medieval era. This was true, firstly because religious practices required and promoted the astronomic conception of time, and secondly, because daily life was dictated by the sun’s movement below and above the horizon. Medieval Europe—with its longstanding adherence to celestial and religious time—also lived according to this double system of equal and unequal hours. As C. Beaune said, the clock, according to this vision, represented ‘a condensed form of the cosmos and cosmological religiosity’.