Whereas this curious theory was accepted by the Aristotelian Al-Biṭrūjī, the author of the pseudo-Aristotelian _Liber de proprietatibus elementorum_ vigorously opposed to it the following argument.[351] If the fixed stars revolve around the earth in 36,000 years, the land ought to revolve around the 34,000 miles which he believed make the circumference of the earth in the same time, or, as we may infer, at a rate of slightly less than a mile per year. We should therefore expect to find certain cities much nearer the coast and other cities farther from the coast than they used to be. The anonymous author says that if the theory were valid one ought to be able to observe great changes in the position of such places as Arin, Ceylon, Byzantium, and Rome in relation to the sea. But since, as a matter of fact, no such changes are apparent, the whole theory of the transposition of land and sea falls to the ground. Obvious as it may seem to us, this reasoning is remarkable at a time when actual observation as a foundation for, or check on, theorizing was rare indeed; and hence it is gratifying to note that the _Liber de proprietatibus elementorum_ with its argument against the Great Year, rather than the encyclopedia of the “Brothers of Piety and Sincerity” with its argument for it, was the work on this subject that was read by Occidental scholars. THEORIES OF THE TIDES The Moslems did not add much to the classical theories of the tides which they transmitted to Christendom. Their fundamental work concerning tides was that treatise of Abū Maʿshar which we have already mentioned, a work from which, as Duhem says, all the Middle Ages learned the laws of the ebb and flood.[352] Here, in the chapters on the moon,[353] a full description is given of the various characteristics of the tides together with copious speculations regarding their causes. The actual observations of fact were exact and careful. Abū Maʿshar explains with not a little accuracy the relation of the tides to the moon’s rising and setting, to her phases, and to the position of the sun; he understood that winds might cause exceptionally high water; he recognized the influences of local topographic features, that some seas display different tidal phenomena from others and that the flood waters may be retained by reefs, or valleys, or deep bays. On the other hand, Abū Maʿshar’s treatment of the causes of the tides was less successful. Though he believed firmly that the moon produces the ebb and flood, he failed to account for the presence of the high tide at the time of the moon’s opposition. His explanation of the moon’s attraction of the waters was in keeping with astrological methods of reasoning. Our satellite was supposed by astrologers to be of peculiarly aqueous nature and for that reason exceptionally capable of governing the movements of the liquid element of the earth.