The Kitāb al-Tabṣira fī ˁilm al-nujūm (“Enlightenment in the science of the stars”) was written in 13th century Yemen by al-Ashraf ˁUmar (d. 1296), who ruled during the last two years of his life over this region as the third of the Rasūlid sultans. In his treatise, he includes a wide range of topics and deals with astronomical, astrological, mathematical, and geographical knowledge as well as calculating, prognostic, and magic practises.
This talk will focus on chapter xlvi of the Tabṣira that discusses the use of water-clocks to determine ascendant and hour “while (there are) clouds”. After shortly introducing the author, his oeuvre, and his treatise, this talk will focus on the description of the water-clock and its use as provided in this chapter. In a short outlook, this talk will then present further evidence of this instrument’s use for astrological purposes as found in the sources, e.g., in the Mujmal al-uṣūl fī aḥkām al-nujūm (“The compendium of the principles in astrology”) by Kūshyār b. Labbān (fl. 1000). This material will open up a whole array of scientific and cultural questions including that for possible users and the role of exactness in astrology.

This talk attempts to map the journey of time as told by the water clocks of ancient Egypt. More than twenty outflow water clocks of the type developed in ancient Egypt have been described. The earliest exemplar is the Karnak water clock, counting twelve hours of the night inscribed with the cartouches of Amenhotep III, which places it in the 18th dynasty of the New Kingdom, around 1375 BCE. The existence of such water clocks is pushed back to around 1500 BCE by a tomb biography which claims the invention of a seasonally-adjusted vessel of the same truncated cone shape as the Karnak version. At the other end of the instrument’s timeline are water clocks of the same shape and function inscribed to Ptolemy II, and even later ones which pseudo-archaically use cartouches of earlier rulers.

Egyptian-style water clocks have not just been found in Egypt, but also around the Eastern Mediterranean and possibly as far east as Nineveh. At a similar time to this spread of instruments, the classical world was adopting timekeeping and astronomy concepts from both Egypt and Mesopotamia. Egyptian astronomical ideas were arguably less prominent in this process than Mesopotamian astronomy, but the Egyptian timekeeping pattern of 12 daylight +12 night ‘hours’ per day was adopted, becoming the 24-hour system that we still use. Tracing the dispersion of water clocks could help reconstruct some of the narrative behind this ancient knowledge transfer.

Direct evidence for Babylonian water clocks is scanty – no preserved water clocks have been identified and references to them in textual sources are limited to a few mentions in literary texts, a section of a lexical text, and two mathematical problems concerning the volume of water held within a water clock. Nevertheless, the large number of timed astronomical observations recorded in first millennium BC sources have generally been assumed to have been made using a water clock. In this presentation I will review what little we know of Babylonian water clocks and look at whether this information is compatible with the assumption that water clocks were used extensively in astronomical observation.