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Arabian Studies V
earlier Egyptian, Syrian, and Yemeni sources. Such a compendium
is ol considerable interest to historians of science for the informa-
uon u contains on earlier works that are no longer extant in their
original form. Various other later Yemeni works of an eclectic
nature survive either complete or in fragmentary form in the manu­
script sources and remain to be properly studied, including zij
handbooks for San‘a\ Zabld, and Ta‘izz.
The last Yemeni zij handbooks were compiled for SaiTa’ in the
mid-seventeenth century by the brothers al-Hasan and ‘Abdullah
al-SarJii, relying entirely on earlier Yemeni zij handbooks. In
San‘a’ today there is still a small group of elderly people who have
received instruction on the zij handbooks of the brothers al-Sarhi.
Besides this sophisticated tradition of mathematical astronomy
the Yemeni astronomers maintained an interest in traditional folk
astronomy and simple timekeeping using shadow lengths by day
and the lunar mansions by night. Thus, for example, the thirteenth
century astronomer al-Farisi wrote a treatise on these two topics as
well as his zij. In medieval Yemeni almanacs simple tables were
sometimes given for reckoning time of night by the lunar mansions.
In the courtyard of the mosque of al-Janad north of Ta‘izz there
is a stone gnomon about the height of a man,* with which the time
of day could be reckoned using simple rules originally adopted
from Indian astronomy, and the time of the midday and afternoon
prayers, both defined in terms of shadow lengths, could also be
regulated. Using one eleventh-century Yemeni treatise on simple
techniques of timekeeping with such a gnomon it has been possible
to explain the origin of the definitions of the times of the daytime
prayers in Islam.7
In the Yemen, as elsewhere in the Islamic world, mathematical
astronomy declined from about the fifteenth century onwards. The
works of the early Yemeni astronomers were thereafter forgotten
and in some cases lost. Fortunately, enough Yemeni manuscripts
survive in libraries in Europe and the Near East to enable us to
document a substantial part of this tradition for the first time.

*This gnomon is known locally as ‘Asa Mu‘adh b. Jabal, ihc ‘stick of this cele­
brated Companion of the Prophet despatched by him to the Yemen [R.B.S.J

Notes

The research on Islamic science conducted at the American Research Center in
Egypt during the years 1972-6 was supported by the Smithsonian Institution and the
National Science Foundation, Washington, D.C. Research >n the libraries of the