Gersonides. Like most Jewish philosophers, he earned his bread by
practicing medicine, and realized Hippocrates's ideal of the
physician-philosopher. Born at Bagnols (1288) in a family of scholars,
he lived nearly all his life in Orange, Perpignan, and Avignon,
where he worked in peace under the protection of the popes. There
was hardly a science that he did not deal with, hardly a problem in
philosophy that he left untouched. He was a learned Talmudist, he
contributed to the mathematics of music, he wrote poetry.
In mathematics and astronomy he was among the lights of the age.
He anticipated (1321) the method later formulated by Maurolico
(1575) and Pascal (1654), of finding the number of simple permutations
of n objects by mathematical induction. His treatise on trigonometry
paved the way for Regiomontanus, and was so widely esteemed that
Pope Clement VI commissioned its translation into Latin as De
sinibus, chordis, et arcubus (1342). He invented, or materially
improved, the cross-staff for measuring the altitude of stars; this
remained for two centuries a precious boon to navigation. He made
his own astronomic observations, and ably critized the Ptolemaic
system. He discussed but rejected the heliocentric hypothesis, in a
manner suggesting that there were quite a few adherents of it in his
time. He perfected the camera obscura, and used it, with the
cross-staff, to determine more accurately the variations in the
apparent diameter of the sun and moon.
As ben Gerson's science stemmed from the Arabic mathematicians and
astronomers, so his philosophy was based on a critical study of the
commentaries in which Averroes had expounded Aristotle. During the
years 1319-21 Levi composed commentaries on these commentaries,
covering Aristotle's treatises on logic, physics, astronomy,
meteorology, botany, zoology, psychology, and metaphysics; and to
these studies he added, of course, repeated readings of Maimonides.
His own philosophy, and most of his science, were embodied in a Hebrew
work entitled, in the fashion of the age, Milchamoth Adonai
( Battles of the Lord, 1317-29). It ranks second only to the Moreh
Nebuchim in Jewish medieval philosophy, and continues Maimonides's
attempt to reconcile Greek thought with Jewish faith, much to the
detriment of the faith. When we consider the similar efforts of
Averroes and Thomas Aquinas to harmonize Mohammedanism and