| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, p. 659 |
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Courtesy of 
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Kūhī: Abū
Sahl Wījan ibn Rustam [Wustam]
al‐Kūhī [al‐Qūhī]
Len Berggren
Flourished second half
of the 10th century
Kūhī
attained distinction as an astronomer who was skilled in observational instruments,
and his work was well known among the astronomers and mathematicians of his
age working in the Būyid domains of ʿIrāq
and western Iran. Born in Tabaristan, he was supported by three kings of the
Būyid Dynasty: ʿAḍud
al‐Dawla, Ṣamṣām
al‐Dawla, and Sharaf al‐Dawla, whose combined reigns cover the
period 962–989. Thus, Kūhī probably did most of his work in the
second half of the 10th century.
Ibn
al‐Haytham
and Bīrūnī knew of several
of Kūhī's works, and later ʿUmar al‐Khayyām cites him as one of the “distinguished mathematicians
of ʿIrāq” (Sesiano, p. 281). In 969/970 Kūhī assisted in
Ṣūfī's observations in Shīrāz
to determine the obliquity of the ecliptic, as well as in other observations
of the Sun's movement, done on the order of ʿAḍud
al‐Dawla. And in 988/989 he was director of the observatory that ʿAḍud's
son, Sharaf al‐Dawla, built in Baghdad, which was intended to observe
the Sun, Moon, and the five known planets.
According
to Bīrūnī, Kūhī constructed for solar observations
a house whose lowest part was in the form of a segment of a sphere of diameter
25 cubits (approximately 13 m) and whose center was in the ceiling of the
house. Sunlight was let in through an opening at that center point of the
sphere, which was located in the roof.
Three
of Kūhī's works deal directly with problems that might be called
astronomical. They are: (1) On What Is Seen of Sky and Sea (published
in Rashed), (2) On Rising Times (published in Berggren and Van Brummelen),
and (3) On the Distance from the Center of the Earth to the Shooting Stars
(published in Van Brummelen and Berggren). The first treats the visible horizon
and shows how, knowing the height of a lighthouse on an island, one can calculate
how far away its light can be seen (and related problems). In the second he
shows how one can calculate the rising times and ortive amplitudes of the
zodiacal signs by Menelaus's theorem. In the third he uses parallax to show
how to calculate the distance to meteors. (Kūhī's technique was
rediscovered in 1798 by Johann
Benzenberg and Heinrich
Brandes in Germany, who settled the ancient question of whether or
not meteors were atmospheric phenomena.) In none of them, however, is any
observational data cited, nor are any numerical examples worked. A fourth
work, dealing with the astrolabe (published in Berggren), discusses the geometry
of that instrument. In particular, it solves problems demanding the construction
of certain lines or points of a planispheric astrolabe given other lines and
points. A fifth work, applying a method for computing the direction of Mecca,
which became common in astronomical works known as zījes, has
been ascribed to Kūhī. But the detailed computations carried out
are entirely out of character with his other works and so the attribution
must, for the present, be regarded as spurious.
Although
Kūhī's work was studied by Islamic scholars as late as the 18th
century (notably Muḥammad ibn Sirṭāq
in the first half of the 14th century and Muṣṭafā Ṣidqī in the 18th century),
it – like that of many of his distinguished contemporaries and successors
in the eastern regions – was unknown in the west.
Selected References
Al‐Qifṭī,
Jamāl al‐Dīn (1903). Taʾrīkh al‐ḥukamāʾ, edited
by J. Lippert. Leipzig: Theodor Weicher, pp. 351–354.
Berggren, J. L. (1994). “Abū Sahl al‐Kūhī's
Treatise on the Construction of the Astrolabe with Proof: Text, Translation
and Commentary.” Physis 31: 141–252.
Berggren, J. L. and Glen Van Brummelen (2001). “Abū Sahl
al‐Kūhī on Rising Times.” SCIAMVS 2: 31–46.
Ibn al‐Nadīm (1970). The Fihrist of al‐Nadīm:
A Tenth‐Century Survey of Muslim Culture, edited and translated
by Bayard Dodge. 2 Vols. New York: Columbia University Press.
Rashed, Roshdi (2001). “Al‐Qūhī: From Meteorology
to Astronomy.” Arabic Sciences and Philosophy 11: 157–204.
Sayılı, Aydın (1960). The Observatory in Islam.
Ankara: Turkish Historical Society, esp. pp. 106, 112–117.
Sesiano,
J. (1979). “Note sur trois théorèmes de mécanique d'al‐Qūhī
et leur conséquence.” Centaurus 22:
281–297.
Sezgin, Fuat (1974). Geschichte des arabischen Schrifttums.
Vol. 5, Mathematik, pp. 314–321. Leiden: E. J. Brill.
Van Brummelen, Glen and J. L. Berggren (2001). “Abū Sahl
al‐Kūhī on the Distance to the Shooting Stars.” Journal
for the History of Astronomy 32: 137–151.