While the primitive chemical practice followed the progress of the arts which it served, the new theory of alchemy, with the ever-growing tradition of fantastic experiments arising out of it, found different and less direct channels in its descent from ancient to modern times. It has been customary to speak of the Arabs as if that nation had been the chief means of transmitting the knowledge of Greek doctrine to our mediæval scholars, but we now know that there was a previous link in the chain of intellectual succession. This was supplied by the care and industry of the Syrian subjects of the early Caliphs, nor did their learned men play a less important part in the history of chemistry than in that of the other sciences. Sergius of Resaina, a scholar of the fifth century, was, it is said, the first Syrian who attempted to translate the Greek chemists, several of whom mention him by name. The chief development of this work belongs, however, to the ninth and tenth centuries, and its glory must ever remain with the great school of Bagdad. Chemical treatises composed by Democritus and Zosimus[113] were there and then rendered into Syriac, as may be seen by the manuscripts still preserved in the British Museum and at Cambridge. It was not long before the Arabs themselves began to feel powerfully the intellectual impulse thus communicated to them in the heart of a country which they had made their own. Khaled ben Yezid ibn Moauia, who died in the year 708, is said by their historians to have been the first of that nation who devoted his attention to chemistry. In his case the filiation of doctrine would seem very plain, as he was the pupil of a Syrian monk named Mariannos. Djabar, the _Geber_ of Western writers, followed in the same line of study, and from the ninth century there was a regular school of Arabian chemists whose labours may be studied in the manuscript collections of Paris and Leyden. In the eleventh century appeared a curious phenomenon, in the shape of a dispute among the Arabians of that day regarding the truth of the tradition which pronounced the transmutation of metals possible. The unwearied but still unavailing experiments which had now been carried on through several ages, produced at last their inevitable effect in the shape of philosophic doubt, eagerly urged on the one part and as eagerly repelled on the other. The chemical school was now divided according to these opposite opinions, and each party in their writings sought to give weight to what they taught by borrowing in support of their arguments the names of the mighty dead. In this conflict it was left to the followers of Rases to sustain the affirmative and to assert the possibility of transmutation. These were the apologists for the past, and the advocates, in the name of their great master, of that hope which had inspired previous research and borne fruit in so many important discoveries.