optics 535complete fulfillment of an ideal of life involving action
and contemplation. In later life he wrote an interpretation
of human history divided into seven ages and envisioned
as a ceaseless combat between good and evil. It dealt with
the ideas of JOACHIM OFFIOREand the coming of the
ANTICHRIST. Always loyal to the church, he even pro-
moted a radical ideal of papal infallibility, especially on
certain questions of importance to the Franciscans. He
vigorously denounced corruption and made a compari-
son of the church “of this world” to the biblical Babylon.
After his death in 1298, some of his ideas were con-
demned at the Council of VIENNAin 1311 and more at
Bern in 1326. His tomb, long a place of PILGRIMAGE, was
destroyed and his remains scattered. His ideas on poverty
continued to be influential within the Franciscan order
long after his death.
See alsoBIBLE;CLEMENTV, POPE;JOHNXXII, POPE;
SPIRITUALFRANCISCANS.
Further reading:David Burr, Olivi and Franciscan
Poverty: The Origins of the Usus Pauper Controversy
(Philadelphia: University of Pennsylvania Press, 1989);
David Burr, Olivi’s Peaceable Kingdom: A Reading of the
Apocalypse Commentary (Philadelphia: University of
Pennsylvania Press, 1993); Decima L. Douie, The Nature
and the Effect of the Heresy of the Fraticelli(Manchester:
Manchester University Press, 1932).
Omar, Mosque of(Umar) SeeDOME OF THEROCK.
Omar I, Abu Hafsa ibn al-Khattab SeeUMAR IBN AL-
KHATTAB.
Omar Khayyam (Ghiyath al-Din Abul-Fath Umar ibn
Ibrahim al-Khayyami, Umar-I Khayyam, Omar the Tent-
maker)(ca. 1048–1131/32)Persian astronomer, mathe-
matician, poet
Omar Khayyam was probably born at Nishapur in IRANin
about 1048. He was well educated there and later at
SAMARKAND. He won wide recognition for treatises on
algebra and astronomy. The SELJUKruler of Persia, Malik
Shah (r. 1055–92), was so impressed by his knowledge
that he called him to his palace and commissioned him to
reform the CALENDARusing astronomical observations.
He finished that in 1079 and then constructed an obser-
vatory at Isfahan.
In 1092, after the death of Malik Shah, Omar went on
pilgrimage to MECCA. When he returned home to Nisha-
pur, he lived a reclusive life, and wrote his poetic master-
piece the Rubaiyat(Quatrains). These poems were only
gradually collected and his status as a great poet only grad-
ually evolved. Ultimately he became recognized as one of
the greatest poets of the Middle Ages. He left retirement
only to do some weather forecasting for a sultan worried
about prospects for hunting activities. Throughout his life
he was said to prefer reason to revelation. He died in
1131/32 and was buried at Isfahan, where his tomb
became a symbol of Persian identity. His calendar, the
Malikior Jalali,of 1079 was considered among the most
accurate of the Middle Ages, and may be more precise than
the Gregorian calendar developed 500 years later.
Further reading: Omar Khayyam, The Rubiyat of
Omar Khayyam,trans. Peter Avery and John Heath-Stubbs
(New York: Penguin Books, 1979); Ali Dashti, In Search of
Omar Khayyam,trans. L. P. Elwell-Sutton (London: G.
Allen and Unwin, 1971); John Andrew Boyle, “Umar
Khayyam: Astronomer, Mathematician and Poet,” in The
Cambridge History of Iran.Vol. 4. The Period from the Arab
Invasion to the Saljuks,ed. R. N. Frye (Cambridge: Cam-
bridge University Press, 1975), 658–664; Otto Rothfield,
Umar Khayyam and His Age(Bombay: D.B. Taraporevala,
1922); Rushdi Rashid, Omar Khayyam, the Mathematician
(New York: Bibliotheca Persica Press, 2000).optics The theories of PLATO were fundamental in
medieval optics until the 11th century. According to
Plato, a ray was sent out uninterruptedly by the eye. It
originated in a human inner fire. Called the theory of
emission, it was accepted first by AUGUSTINEand then
over the course of the Middle Ages by William of
Conches (ca. 1100–54), ADELARD OFBATH, and Robert
GROSSETESTE. However, when the anatomy of the eye
became known, it brought this into question. At the same
time, the work of ARISTOTLEand his Arabic commentators,
such as IBNSINA(Avicenna) and IBNRUSHD(Averroës),
led to a better understanding of optics. According to Avi-
cenna luxwas the quality of bodies that emitted light and
lumen was the optical effect this provoked. After the
ancient works of Euclid and Ptolemy on optics became
available in the Latin West from the mid-12th century,
Optics began to be studied from the point of view of
geometry. Authors concentrated their attention on the
path followed by a ray of vision explaining it by the laws
of perspective, reflection, and refraction. This thought
produced a science of perspective in the 13th century.
The works of such scholars as Roger BACON, John
Peckham (1225–92), Witelo (ca. 1230–78), and Henry of
Langenstein (d. 1397) were essentially based on the ideas
of the Arab scholar IBN AL-HAYTHAM(Alhazen).
There remained the problem of color. After Roger
Bacon, Witelo, and John Peckham, a DOMINICAN,
Theodoric of Freiberg, in 1304, proposed a theory draw-
ing together the laws of the reflection and refraction of
rays as seen in a rainbow. To understand colors, he con-
structed six-angled prisms. The existence of such knowl-
edge that permitted the making of lenses from about
1280 to improve vision. Optics remained primarily a the-
oretical discipline.
See alsoAL-KINDI, ABUYUSUFYAQUB IBNISHAQ AL-
SABBAH; LENSES AND EYEGLASSES.