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.

[Sidenote: Review of the works of Alhazen.] Among such writers is
Alhazen; his date was about A.D. 1100. It appears that he resided both
in Spain and Egypt, but the details of his biography are very confused.
Through his optical works, which have been translated into Latin, he is
best known to Europe. [Sidenote: He corrects the theory of vision.] He
was the first to correct the Greek misconception as to the nature of
vision, showing that the rays of light come from external objects to the
eye, and do not issue forth from the eye, and impinge on external
things, as, up to his time, had been supposed.