So acute and irreconcilable were the racial differences between Arabs and Persians that one is astonished to see how thoroughly the latter became Arabicised in the course of a few generations. As clients affiliated to an Arab tribe, they assumed Arabic names and sought to disguise their foreign extraction by fair means or foul. Many provided themselves with fictitious pedigrees, on the strength of which they passed for Arabs. Such a pretence could have deceived nobody if it had not been supported by a complete assimilation in language, manners, and even to some extent in character. On the neutral ground of Muḥammadan science animosities were laid aside, and men of both races laboured enthusiastically for the common cause. When at length, after a century of bloody strife and engrossing political agitation, the great majority of Moslems found themselves debarred from taking part in public affairs, it was only natural that thousands of ardent and ambitious souls should throw their pent-up energies into the pursuit of wealth or learning. We are not concerned here with the marvellous development of trade under the first ‘Abbásid Caliphs, of which Von Kremer has given a full and entertaining description in his _Culturgeschichte des Orients_. It may be recalled, however, that many commercial terms, _e.g._, tariff, names of fabrics (muslin, tabby, &c.), occurring in English as well as in most European languages are of Arabic origin and were brought to Europe by merchants from Baghdád, Mosul, Baṣra, and other cities of Western Asia. This material expansion was accompanied by an outburst of intellectual activity such as the East had never witnessed before. It seemed as if all the world from the Caliph down to the humblest citizen suddenly became students, or at least patrons, of literature. In quest of knowledge men travelled over three continents and returned home, like bees laden with honey, to impart the precious stores which they had accumulated to crowds of eager disciples, and to compile with incredible industry those works of encyclopædic range and erudition from which modern Science, in the widest sense of the word, has derived far more than is generally supposed. [Sidenote: Development of the Moslem sciences.]