1. Euclid and Ptolemy, Hippocrates and Galen, some portion of Aristotle, and, in addition, an abundant Neo-Platonic Literature,—indicate the elements of Arabic Natural Philosophy. It is a popular philosophy, which, chiefly through the instrumentality of the Sabaeans of Harran, found acceptance with the Shiʻites and other sects, and which in due course impressed not only court circles, but also a large body of educated and half-educated people. Stray portions of it were taken from the writings of the “Logician”,—Aristotle,—e.g. from the “Meteorology”, from the work “On the Universe”, which has been attributed to him, from the “Book of Animals”, from the “Psychology”, and so on; but its general character was determined by Pythagorean-Platonic teaching, by the Stoics, and by subsequent astrologers and alchemists. Human curiosity and piety were fain to read the secrets of the Deity in the book of his Creation, and they proceeded in this search far beyond practical requirements, which merely called for a little arithmetic to serve in the division of inheritances and in trade, and a little astronomy besides, to determine the proper times for celebrating the functions of religion. Men hastened to gather wisdom from every quarter, and in so doing they manifested a conviction, which Masudi accurately expressed, when he said: “Whatever is good should be recognized, whether it is found in friend or foe”. Indeed Ali, the prince of believers, is reported to have said: “The wisdom of the world is the believer’s strayed sheep: take it back, even though it come from the unbelieving”. 2. Pythagoras is the presiding genius of Mathematical study in Islam. Greek and Indian elements are mingled in it, it is true, but everything is regarded from a Neo-Pythagorean point of view. Without studying such branches of Mathematics, as Arithmetic and Geometry, Astronomy and Music, no one, they said, becomes a philosopher or an educated physician. The Theory of Numbers,—prized more highly than Mensuration, because it appeals less to the outward vision, and should bring the mind nearer the essence of things,—gave occasion to the most extravagant puerilities. God is, of course, the great Unity, from whom everything proceeds, who himself is no number, but who is the First Cause of Number. But above all, the number Four,—the number of the elements and so on,—was held in high favour by the philosophers; and by-and-by nothing in heaven or earth was spoken of or written about, except in sentences of four clauses and in discourses under four heads.