Very speedily the intolerant self-sufficiency of the early days of faith, which made the Koran seem the only possible book, was dropped. Learning sprang up everywhere in the footsteps of the Arab conquerors. By the eighth century there was an educational organization throughout the whole “Arabized” world. In the ninth learned men in the schools of Cordoba in Spain were corresponding with learned men in Cairo, Bagdad, Bokhara and Samarkand. The Jewish mind assimilated very readily with the Arab, and for a time the two Semitic races worked together through the medium of Arabic. Long after the political break-up and enfeeblement of the Arabs, this intellectual community of the Arab-speaking world endured. It was still producing very considerable results in the thirteenth century. VIEW OF CAIRO MOSQUES VIEW OF CAIRO MOSQUES _Photo: Lehnert & Landrock_ So it was that the systematic accumulation and criticism of facts which was first begun by the Greeks was resumed in this astonishing renascence of the Semitic world. The seed of Aristotle and the museum of Alexandria that had lain so long inactive and neglected now germinated and began to grow towards fruition. Very great advances were made in mathematical, medical and physical science. The clumsy Roman numerals were ousted by the Arabic figures we use to this day and the zero sign was first employed. The very name algebra is Arabic. So is the word chemistry. The names of such stars as Algol, Aldebaran and Boötes preserve the traces of Arab conquests in the sky. Their philosophy was destined to reanimate the medieval philosophy of France and Italy and the whole Christian world. The Arab experimental chemists were called alchemists, and they were still sufficiently barbaric in spirit to keep their methods and results secret as far as possible. They realized from the very beginning what enormous advantages their possible discoveries might give them, and what far-reaching consequences they might have on human life. They came upon many metallurgical and technical devices of the utmost value, alloys and dyes, distilling, tinctures and essences, optical glass; but the two chief ends they sought, they sought in vain. One was “the philosopher’s stone”—a means of changing the metallic elements one into another and so getting a control of artificial gold, and the other was the _elixir vitœ_, a stimulant that would revivify age and prolong life indefinitely. The crabbed patient experimenting of these Arab alchemists spread into the Christian world. The fascination of their enquiries spread. Very gradually the activities of these alchemists became more social and co-operative. They found it profitable to exchange and compare ideas. By insensible gradations the last of the alchemists became the first of the experimental philosophers.