Under the Sassanian kings, Persia had become an active centre of intellectual life, reaching the climax of its Augustan age in the reign of Chosroes. Jew, Greek, and Christian alike had welcome at his court, and translations of the writings of the Indian sages completed the eclecticism of that enlightened monarch. Then came the ruthless Arab, and philosophy and science were eclipsed. But with the advent of the Abbaside Khalifs, who number the famous Haroun al-Raschid among them, there came revival of the widest toleration, and consequent return of intellectual activity. Baghdad arose as the seat of empire. Situated on the high road of Oriental commerce, along which travelled foreign ideas and foreign culture, that city became also the Oxford of her time. Arabic was the language of the conquerors, and into that poetic, but unphilosophic, tongue, Greek philosophy and science were rendered. Under the rule of those Khalifs, says Renan, "nontolerant, nonreluctant persecutors," free thought developed; the _Motecallenim_ or "disputants" held debates, where all religions were examined in the light of reason. Aristotle, Euclid, Galen, and Ptolemy were text-books in the colleges, the repute of whose teachers brought to Baghdad and Naishapur (dear to lovers of "old" Khayyám) students westward from Spain, and eastward from Transoxiana. "Arab" philosophy, therefore, is only a name. It has been well described as "a system of Greek thought expressed in a Semitic tongue; and modified by Oriental influences called into existence by the patronage of the more liberal princes, and kept alive by the zeal of a small band of thinkers." In the main, it began and ended with the study of Aristotle, commentaries on whom became the chief work of scholars, at whose head stands the great name of Averroes. Through these--a handful of Jews and Moslems--knowledge of Greek science, of astronomy, algebra, chemistry, and medicine, was carried into Western Europe. By the latter half of the tenth century, one hundred and fifty years after the translation of Aristotle into Arabic, Spain had become no mean rival of Baghdad and Cairo. Schools were founded; colleges to which the Girton girls of the period could repair to learn mathematics and history were set up by lady principals; manufactures and agriculture were encouraged; and lovely and stately palaces and mosques beautified Seville, Cordova, Toledo, and Granada, which last-named city the far-famed Alhâmra or Red Fortress still overlooks. Seven hundred years before there was a public lamp in London, and when Paris was a town of swampy roadways bordered by windowless dwellings, Cordova had miles of well-lighted, well-paved streets; and the constant use of the bath by the "infidel" contrasted with the saintly filth and rags which were the pride of flesh-mortifying devotees and the outward and odorous signs of their religion. The pages of our dictionaries evidence in familiar mathematical and chemical