In their acquaintance with the mechanical arts the Sicilians were not inferior to their most accomplished contemporaries. Their hydraulic system was provided with all the appliances which had been tested by those nations whose arid soil required the artificial stimulus of irrigation. Their mills dotted the banks of every stream whose current afforded sufficient motive power for the propulsion of a water-wheel. The products of their looms were famous for their exquisite patterns and the fineness of their texture. They seemed to have also excelled in the invention and manufacture of contrivances for the measurement of time. A clepsydra belonging to Roger II. has been commemorated by an inscription which would indicate that it equalled in ingenuity and perfection the famous one presented by Harun-al-Raschid to Charlemagne. The hours were marked off by automatons, which dropped a corresponding number of balls into a metallic basin, a not unworthy predecessor of the modern clock. A considerable number of the astrolabes, which, having fortunately escaped the effects of ecclesiastical fury wreaked upon them as magical instruments and devices of Satan, are now preserved in the museums of Europe, are of undoubted Sicilian origin. Abu-Layth, an architect and engineer, who had been educated in the schools of Sicily, assisted in the completion of the great mosque of Seville, erected during the twelfth century, and the globes of gilded bronze which crowned the summit of the Giralda, whose extraordinary dimensions and perfect symmetry excited the wonder of all beholders, were cast and raised to their places under his supervision. The superiority of the Sicilian Moslems in the construction and management of military engines has been already referred to in these pages.