Starting with the notion of the world as a disc, or a ball, the centre of the universe, round which moved six celestial circles, of the Meridian, the Equator, the Ecliptic, the two Tropics, and the Horizon, the Arab philosophers on the side of the earth's surface worked out a doctrine of a Cupola or Summit of the world, and on the side of the heavens a pseudo-science of the Anoua or Settings of the Constellations, connected with the twelve Pillars of the Zodiac and the twenty-eight Mansions of the Moon.
With Arabic astrology we are not here concerned; it is only worth noting in this connection as the possible source of early Christian knowledge of the Southern Cross and other stars famous in the story of exploration, such as Dante shows in the first canto of his Purgatorio. But the geographical doctrines of Islam, compounded from the Hebrew Pentateuch and the theoretical parts of Ptolemy, had a more immediate and reactionary effect on knowledge. The symmetrical Greek divisions of land into seven zones or climates; and of the world's surface,[10] into three parts water and one part terra firma; the Indian fourfold arrangement of "Romeland" and the East; the similar fourfold Chinese partition of China, India, Persia, and Tartary: all these reappeared confusedly in Arabic geography. From India and the Sanscrit "Lanka," they seem to have got their first start on the myth of Odjein, Aryn, or Arim, "the World's Summit"; from Ptolemy the sacred number of 360 degrees of longitude was certainly derived, beautifully corresponding to the days of the year, and neatly divided into 180 of land or habitable earth and 180 of sea, or unharvested desert. With the seven climates they made correspond the great Empires of the world—chief among which they reckoned the Caliphate (or Bagdad), China, Rome, Turkestan, and India.
The sacred city of Odjein had been the centre of most of the earlier Oriental systems; in the Arabic form of Arim ("The Cupola of the Earth"), it became the fixed point round which circled mediæval theories of the world's shape. "Somewhere in the Indian Ocean between Comorin and Madagascar," became the compromise when the mountain could not be found off any of the known coast-lines; it was mixed up with notions of the Roc, and the Moon Mountains in Africa, of the Magnet Island and of the Eastern Kingdom made out of one vast pearl; and even in Roger Bacon it serves as an algebraic sign for a mathematical centre of the world.
The enlargement of knowledge, though forcing upon Arabic science a conviction of Ptolemy's mistake in over-extending the limits of the world known to him, only led to the invention of a scholastic distinction between the real and the traditional East and West, while the confusion was made perfect by the travestied history always so popular among Orientals. The "Gades of Alexander and Hercules," the farthest points east and west, were named after the mythical conquests of the real Iskander and the mythical hero of Greeks and Phœnicians. Arim in the middle, with the pillars of Hercules and Alexander, and the north and south poles at equal distance from it—the centre and the four corners of the world as neatly fixed as geometry could define—this was the map, first of the Arabs, and then of their Christian scholars.
To form any idea of the complete spell thus cast over thought both in Islam and Christendom, we may look at the words of European scholars of the twelfth and thirteenth centuries, living far from Islam, long after its intellectual glory had begun to decay, and at a time when Christian scholastic philosophy had reached an independent position. Gerard of Cremona and Adelard of Bath (the translator of the great Arabic geographer, Mohammed Al-Kharizmy) in the twelfth century, Roger Bacon and Albertus Magnus in the later thirteenth, are all as clear about their geographical postulates as about their theological or ethical rules. And what concerns us here is that they exactly reflect the mind of the Arabic science or pseudo-science of the time just preceding, so that their words may represent to us the state of Mohammedan thought between the eighth and twelfth centuries, between the writers at the Court of Caliph Almamoun (813-833) and Edrisi at the Court of King Roger of Sicily (1150).
(1.) Adelard, summarising Mohammed Al-Kharizmy with the results of his Paris education, tells us of the Arabic "Examination of planets and of time, starting from the centre of the world, called Arim, from which place to the four ends of the earth the distance is equal, viz., ninety degrees, answering to the fourth part of the world's circumference. It is tedious and unending to attempt to place all the countries of the world and to fix all the marks of time. So the meridian is taken as the measure of the latter and Arim of the former, and from this starting-point it is not hard to fix other countries." "Arim," he concludes, "is under the equator, at the point where there is no latitude," and he plainly implies that there were then existing among the Arabs tables calculating all the chief places of every country from the meridian of Arim.
(2.) Gerard of Cremona, who, though for some time a resident at Toledo, is essentially an Italian, tells us about the "Middle of the World," from which longitudes were calculated, "called Arim," and "said to be in India," whose longitude from west to east or from east to west is ninety degrees.
In his Theory of the Planets Gerard tells us still more wonderful things. Arim was a geographical centre known and used by Hermes Trismegistus and by Ptolemy, as well as by the great Arab geographers; Alexander of Macedon marched just as far to the east of Arim as Hercules to the west; both reached the encircling ocean, and accordingly "Arim is equidistant from both the Gades, 90 degrees; likewise from each pole, north and south, the same, 90 degrees." This all recurs in the tables of Alphonso the Wise of Castille about a.d. 1260, and two of the greatest of mediæval thinkers, Albert and Roger Bacon, reproduced the essential points of this doctrine, its false symmetry, and its balance of the true and the traditional, with variations of their own.
(3.) Albert the Great, Albertus Magnus, second only to Aquinas among the Continental Schoolmen, in his View of Astronomy, repeats Adelard upon the question of Arim, "where there is no latitude," while (4) Roger Bacon discusses not only the true and the traditional East and West, but even a twofold Arim, one "under the solstice, the other under the equinoctial zone." Arim he finds not to be in the centre of the real world, but only of the traditional. In another passage of the Opus Majus, Bacon, our first English worker in the exact sciences, allows the world-summit not to be exactly 90 degrees from the east, although so placed by mathematicians. Yet there is no contradiction, he urges, because the men of theory are "speaking of the habitable world known to them, according to the true understanding of latitude and longitude," and this "true understanding" is "not as great as has been realised in travel by Pliny and others." "The longitude of the habitable world is more than half of the whole circuit." This, reproduced in the Imago Mundi of Cardinal Peter Ailly (1410), fell into the hands of Columbus and helped to fix his doctrines of the shape of the world ("in the form of a pear") of the terrestrial paradise, and of the earth's circumference,—so enormously contracted as practically to abolish the Pacific.[11]
To return to the Arabs: We have seen how they not merely followed Greek theories, which their own experience as conquerors in the Further East went to discredit, but, in the great outlines of geography, added to earlier errors, put prejudice in the place of knowledge, and handed on to Christendom a half-fanciful map of the world. It only remains for us to illustrate their leading fault, of a too vivid fancy, with a few details on minor points.