ce of a simple and correct one. The observations of
later generations have shown conclusively that the sun's shift of
position is regularly progressive, hence that there is no "trepidation"
of the stars and no revolution of the equinoctial points.

If the Arabs were wrong as regards this supposed motion of the fixed
stars, they made at least one correct observation as to the inequality
of motion of the moon. Two inequalities of the motion of this body were
already known. A third, called the moon's variation, was discovered by
an Arabian astronomer who lived at Cairo and observed at Bagdad in 975,
and who bore the formidable name of Mohammed Aboul Wefaal-Bouzdjani.
The inequality of motion in question, in virtue of which the moon moves
quickest when she is at new or full, and slowest at the first and third
quarter, was rediscovered by Tycho Brahe six centuries later; a fact
which in itself evidences the neglect of the Arabian astronomer's
discovery by his immediate successors.

In the ninth and tenth centuries the Arabian city of Cordova, in Spain,
was another important centre of scientific influence. There was a
library of several hundred thousand volumes here, and a college where
mathematics and astronomy were taught. Granada, Toledo, and Salamanca
were also important centres, to which students flocked from western
Europe. It was the proximity of these Arabian centres that stimulated
the scientific interests of Alfonso X. of Castile, at whose instance the
celebrated Alfonsine tables were constructed. A familiar story records
that Alfonso, pondering the complications of the Ptolemaic cycles and
epicycles, was led to remark that, had he been consulted at the time of
creation, he could have suggested a much better and simpler plan for the
universe. Some centuries were to elapse before Copernicus was to show
that it was not the plan of the universe, but man's interpretation of
it, that was at fault.

Another royal personage who came under Arabian influence was Frederick
II. of Sicily--the "Wonder of the World," as he was called by his
contemporaries. The Almagest of Ptolemy was translated into Latin at
his instance, being introduced to the Western world through this curious
channel. At this time it became quite usual for the Italian and Spanish
scholars to understand Arabic although they were totally ignorant of
Greek.

In the field of physical science one of the most important of the
Arabian scientists was Alhazen. Hi