[Sidenote: Obligations to the Khalifs of the West.] Such were the Khalifs of the West; such their splendour, their luxury, their knowledge; such some of the obligations we are under to them--obligations which Christian Europe, with singular insincerity, has ever been fain to hide. The cry against the misbeliever has long outlived the Crusades. Considering the enchanting country over which they ruled, it was not without reason that they caused to be engraven on the public seal, "The servant of the Merciful rests contented in the decrees of God." What more, indeed, could Paradise give them? But, considering also the evil end of all this happiness and pomp, this learning, liberality, and wealth, we may well appreciate the solemn truth which these monarchs, in their day of pride and power, grandly wrote in the beautiful mosaics on their palace walls, an ever-recurring warning to him who owes dominion to the sword, "There is no conqueror but God." [Sidenote: Examination of Mohammedan science.] The value of a philosophical or political system may be determined by its fruits. On this principle I examined in Vol. I., Chapter XII., the Italian system, estimating its religious merit from the biographies of the popes, which afford the proper criterion. In like manner, the intellectual state of the Mohammedan nations at successive epochs may be ascertained from what is its proper criterion, the contemporaneous scientific manifestation. At the time when the Moorish influences in Spain began to exert a pressure on the Italian system, there were several scientific writers, fragments of whose works have descended to us. As an architect may judge of the skill of the ancient Egyptians in his art from a study of the Pyramids, so from these relics of Saracenic learning we may demonstrate the intellectual state of the Mohammedan people, though much of their work has been lost and more has been purposely destroyed.