Thus, on the first of November, 1170, the storm-flood, bursting through the dykes, submerged all the land between the Texel, Medenblik, and Stavoren, formed the island of Wieringen, and enlarged the openings by which the Zuiderzee communicated with the ocean. The inundations of 1232 and 1242 caused, each of them, the death of more than 100,000 persons, and that of 1287 swept away more than 80,000 victims in Friesland alone. The irruption of 1395 considerably widened the channels between the Flie and the Texel, and allowed large vessels to sail as far as Amsterdam and Enkhuizen, which had not been the case before. Whilst reading these accounts, we are led to compare the inhabitants of the Dutch lowlands with those of the fertile fields and vineyards that clothe the sides of Vesuvius: both exposed to sudden and irretrievable ruin from the rage of two different elements, and yet both contented and careless of the future; the first behind the dykes that have often given way to the ocean, the latter on the very brink of a menacing volcano.
The tides which sometimes cause such dreadful devastations on the shores of the North Sea are, as is well known, inconsiderable, or even hardly perceptible in the Mediterranean, and thus many years passed ere the Greeks and Romans first witnessed the grand phenomenon. The Phœnicians, the merchant princes of antiquity, who at a very early period of history visited the isolated Britons,—
"Penitus toto divisos orbe Britannos,"—
and sailed far away into the Indian Ocean, were of course well acquainted with it; but it first became known to the Greeks through the voyage of Colæus, a mariner of Samos, who, according to Herodotus, was driven by a storm through the Straits of Hercules into the wide Atlantic 600 years before Christ. About seventy years after this involuntary discovery, the Phoceans of Massilia, or Marseilles, first ventured to follow on the track of Colæus for the purpose of trading with Tartessus, the present Cadiz; and from that time remained in constant commercial intercourse with that ancient Phœnician colony.
With what eager attention may their countrymen have listened to the wondrous tale of the alternate rising and sinking of the ocean! Such must have been the astonishment of our forefathers when the first Arctic voyagers told them of the floating icebergs, and of the perpetually circling sun of the high northern summer.
Thus the tides became known to the Massilians about five centuries before Christ, but in those times of limited international intercourse, knowledge travelled but slowly from place to place; so that it was not before the conquests of Alexander, which first opened the Red Sea and the Persian Gulf to Grecian trade, that the great marine phenomenon began to attract the general attention of philosophers and naturalists.
The flux and reflux of the sea is evidently so closely connected with the movements and changes of the moon, that the intimate relations between both could not possibly escape the penetrating sagacity of the Greeks. Thus we read in Plutarch, that Pytheas of Marseilles, the great traveller who sailed to the north as far as the Ultima Thule, and lived in the times of Alexander the Great, ascribed to the moon an influence over the tides. Aristotle expressed the same opinion, and Cæsar says positively (Commentaries, De Bel. Gal. book iv. 29,) that the full-moon causes the tides of the ocean to swell to their utmost height. Strabo distinguishes a three-fold periodicity of the tides according to the daily, monthly, and annual position of the moon, and Pliny expresses himself still more to the point, by saying that the waters move as if obeying the thirsty orb which causes them to follow its course.
This vague notion of obedience or servitude was first raised by Kepler to the clear and well defined idea of an attractive power. According to this great and self-taught genius, all bodies strive to unite in proportion to their masses. "The earth and moon would mutually approach and meet together at a point, so much nearer to the earth as her mass is superior to that of the moon, if their motion did not prevent it. The moon attracts the ocean, and thus tides arise in the larger seas. If the earth ceased to attract the waters, they would rise and flow up to the moon."
The general notion of a mutual attraction, however, did no more than point out the way for the solution of the problem, and it was reserved to our great Newton to accomplish the prophecy of his great predecessor, "that the discovery of the true laws of gravitation would be accomplished in a future generation, when it should please the Almighty Creator of nature to reveal her mysteries to man."
Newton was the first who proved that the tide-generating power of a celestial body arises from the difference of the attraction it exerts on the centre and the surface of the earth. Thus it was at once made clear how the water not only rises on the surface facing the moon, but also on the opposite side of the earth, as in the latter case the moon acts more strongly on the mass of the earth than on the waters which cover the hemisphere most distant from her. The evident consequence is that the earth sinks (so to say), on the surface turned from the moon, whereby a deepening of the waters, or, in other words, a rising of the tide, is occasioned.