PHYSICS
49
PHYSICS
and containing instructions on the use of astronomical
instruments, notably the astrolabe, to which instru-
ment Hermann the Lame (1013-5-1) devoted part of
his researches. In the beginning of the twelfth cen-
tury the contributions of Mohammedan science and
philosophy to Latin Christendom became more and
more frequent and important. About 1120 or 1130
Adelard of Bath translated the "Elements" of Euclid,
and various astronomical treatises; in 1141 Peter the
Venerable, Abbot of Cluny, found two translators,
Hermann the Second (or the Dalmatian) and Robert
of Re tines, established in Spain; he engaged them
to translate the Koran into Latin, and in 1143 these
same translators made Christendom acquainted with
Ptolemy's planisphere. Under the direction of
Raimond (Archbishop of Toledo, 1130; d. 1150),
Domengo Gondisalvi (Gonsalvi; Gundissalinus),
Archdeacon of Segovia, began to collaborate with the
converted Jew, John of Luna, erroneously called John
of Seville (Johannes Hispalensis). While John of
Luna applied himself to works in mathematics, he also
assisted Gondisalvi in translating into Latin a part of
Aristotle's physics, the "De Caelo" and the "Meta-
physics", besides treatises by Avicenna, Al-Gazah,
Al-Far&bi, and perhaps Salomon ibn Gebirol (Avice-
bron). About 1134 John of Luna translated Al-
Fergani's treatise "Astronomy ", which was an abridge-
ment of the "Almagest", thereby introducing Chris-
tians to the Ptolemaic system, while at the same time
his translations, made in collaboration with Gondi-
salvi, familiarized the Latins with the physical and
metaphysical doctrines of Aristotle. Indeed the in-
fluence of Aristotle's "Physics" was already apparent
in the writings of the most celebrated masters of the
school of Chartres (from 1121 until before 1155), and
of Gilbert de la Porree (1070-1154).
The abridgement of Al-Fergani's "Astronomy", translated by John of Luna, does not seem to have been the first work in which the Latins were enabled to read the exposition of Ptolemy's system; it was undoubtedly preceded by a more complete treatise, the "De Seientia stellarum" of Albategnius (Al- Battani), latinized by Plato of TivoH about 1120. However, the "Almagest" itself was still unknown. Moved by a desire to read and translate Ptolemy's immortal work, Gerard of Cremona (d. 1187) left Italy and went to Toledo, eventually making the transla- tion which he finished in 1175. Besides the "Alma- gest", Gerard rendered into Latin other works, of which we have a list comprising seventy-four different treatises. Some of these were writings of Greek origin, and included a large portion of the works of Aristotle, a treatise by Archimedes, Euchd's "Ele- ments" (completed by Hypsicles), and books by Hippocrates. Others were Arabic writings, such as the celebrated "Book of Three Brothers", composed by the Beni M<lsa, "Optics" by Ibn Al-Haitam (the Alhazen of the Scholastics), "Astronomy" by Geber, and "De motu octavae sphaera;" by Thabit ibn Kdrrah. Moreover, in order to spread the study of Ptolemaic astronomy, Gerard composed at Toledo his "Theoricae planetarum", which during the Middle Ages became one of the classics of astronomical in- struction. Beginners who obtained their first cos- mographic information through the study of the "Sphajra", written about 1230 by Joannes de Sacro- bosco, could acquire a knowledge of eccentrics and epicycles by reading the "Theorica; planetarum" of Gerard of Cremona. In fact, until the sixteenth century, most astronomical treatises assumed the form of commentaries, either on the "Sphaera", or the "Thcoric;e planetarum".
"Aristotle's philosophy", wrote Roger Bacon in 1267, "reached a great development among the Latins when Michael Scot appeared about 1230, bringing with him certain parts of the mathematical and phys- ical treatises of Aristotle and his learned commen- XII.— 4
tators". Among the Arabic writings made known to
Christians by Michael Scot (before 1291; astrologer
to Frederick II) were the treatises of Aristotle and
the "Theory of Planets", which Alpetragius had com-
posed in accordance with the hypothesis of homo-
centric spheres. The translation of this last work was
completed in 1217. By propagating among the Latins
the commentaries on Averroes and on Alpetragius's
theory of the planets, as well as a knowledge of the
treatises of Aristotle, Michael Scot developed in them
an intellectual disposition which might be termed
Averroism, and , which consisted in a superstitious
respect for the word of Ari.stotle and his commentator.
There was a metaphysical Averroism which, because professing the doctrine of the substantial unity of all human intellects, was in open conflict with Christian orthodoxy ; but there was likewise a physical Averro- ism which, in its blind confidence in Peripatetic physics, held as absolutely certain all that the latter taught on the subject of the celestial substance, re- jecting in particular the system of epicycles and eccen- trics in order to commend Alpetragius's astronomy of homocentric spheres.
Scientific Averroism found partisans even among those whose purity of faith constrained them to strugggle against metaphysical Averroism, and who were very often Peripatetics in so far as was possible without formally contradicting the teaching of the Church. For instance, William of Auvergne (d. 1249), who was the first to combat "Aristotle and his sec- tarians" on metaphysical grounds, was somewhat misled by Alpetragius's astronomy, which, moreover, he understood but imperfectly. Albertus Magnus (1193 or 1205-1280) followed to a great extent the doctrine of Ptolemy, although he was sometimes in- fluenced by the objections of Averroes or affected by Alpetragius's principles. Vincent of Beauvais in his "Speculum quadruplex", a vast encyclopaedic com- pilation published about 1250, seemed to attach great importance to the system of Alpetragius, borrowing the exposition of it from Albertus Magnus. Finally, even St. Thomas Aquinas gave evidence of being ex- tremely perplexed by the theory (1227-74) of eccen- trics and epicycles which justified celestial phenomena by contradicting the principles of Peripatetic physics, and the theory of Alpetragius which honoured these principles but did not go so far as to represent their phenomena in detail.
This hesitation, so marked in the Dominican school, was hardly less remarkable in the Franciscan. Robert Grosseteste or Greathead (1175-1253), whose in- fluence on Franciscan studies was so great, followed the Ptolemaic system in his astronomical writings, his physics being imbued with Alpetragius's ideas. St. Bonaventure (1221-74) wavered between doctrines which he did not thoroughly understand, and Roger Bacon (1214-92) in several of his writings weighed with great care the arguments that could be made to count for or against each of these two astronomical theories, without eventually making a choice. Bacon, however, was familiar with a method of figuration in the system of eccentrics and epicycles which Alhazen had derived from the Greeks; and in this figuration all the motions acknowledged by Ptolemy were traced back to the rotation of solid orbs accurately fitted one into the other. This representation, which refuted most of the objections raised by Averroes against Ptolemaic astronomy, contributed largely to prop- agate the knowledge of this astronomy, and it seems that the first of the Latins to adopt it and expatiate on its merits was the Franciscan Bernard of Verdun (end of thirteenth century), who had read Bacon's writings. In sublunary physics the authors whom we have just mentioned did not show the hesitation that rendered astronomical doctrines so perplexing, but on almost all points adhered closely to Peripatetic _ opinions.
