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DE FLUXU ET REFLUXU MARIS
BY ROBERT LESLIE ELLIS.
Ir was a natural result of the progress of maritime discovery in the sixteenth century, that much was thought and written on the subject of the tides. The reports continually brought home touching the ebb and flow of the sea on far distant shores, not only excited curiosity, but also showed how little the philosophers of antiquity had known of the phenomena which they attempted to explain. Men who dwelt on the shores of an inland sea, and whose range of observation scarcely extended beyond the Pillars of Hercules, were in truth not likely to recognise any of the general laws by which these phenomena are governed. Their authority accordingly in this matter was of necessity set aside; and a number of hypotheses were proposed in order to explain the newly discovered facts. Of these speculations an interesting account is given in the twenty-eighth book of the Pancosmia of Patricius. It is not, however, complete; no mention being made of the hypothesis of Casalpinus, which is in itself a curious one, and which clearly suggested to Galileo his own explanation of the cause of the tides. Otto Casmann, the preface to whose Problemata Marina is dated in 1596, gives a good deal of information on the same subject, some of which however seems to be simply copied from Patricius; but he mentions Casalpinus, whom, as I have said, Patricius omits. Patricius, it may be remarked, is a scrupulously orthodox philosopher, and dedicates his work to Gregory XIV. with many expressions of reverence and submission.
It is perhaps on this account that he has said nothing of Casalpinus, whose works were "improbatæ lectionis" and who seeks to explain the tides, and also certain astronomical phenomena, by denying the orthodox doctrine of the earth's immobility.
The earliest modern writer whom Patricius mentions is Frederick Chrysogonus, whose work on the tides must have been published in 1527. To his account of the phenomena little, according to Patricius, was added by subsequent writers; nor are his statements contradicted by the reports of seafaring men, who however mention certain matters of detail which he had omitted. Of seamen Patricius particularly mentions Peter of Medina and Nicolaus Sagrus, the latter with especial commendation. From Sagrus (but probably through Patricius) Bacon derived some of the statements of the following tract; those, namely, which relate to the progress of the tide-wave from the Straits of Gibraltar to Gravelines. On the day of new moon, according to Sagrus, there is high water along the coast from Tarifa to Rota at an hour and a half after midnight. After mentioning several intermediate places, he says that along the coast of Normandy as far as Calais and Nieuport there is high water at nine, and after a not very distinct statement as to the time of high water in the middle of the channel, goes on to state that from Calais to Gravelines the water is high off shore (in derotâ) at an hour and a half after midnight, that is at the same time as at Rota, and at Zealand at the same time as on the coast of Portugal. These statements are scarcely sufficiently accurate to make it worth while to compare them with modern observations; but it is necessary to remark that Sagrus, though he mentions it as a remarkable circumstance that the time of high water should be the same at Gravelines and at Rota, does not mean to assert that there is any discontinuity in the progress of the tide along the shores of France and the Netherlands. The tide gets progressively later and later until we come to a place where there is high water about one in the afternoon, and therefore also high water about half-past one after the succeeding midnight. In order to compare Gravelines and Rota, he takes (but without mentioning that he does so) two different tide-waves, the statement with reference to Gravelines appearing to relate to a later wave than the other. Bacon however does