The Tides

These phenomena have, in all ages, excited curosity, aud in many instances they have produced wonder at their extraordinary height and fury. It is related of the soldiers of Alexander the Great, who were natives of the Mediterranean shores, that when they reached the confines of the Indian ocean, and saw its waters rollirg up to a great height, and then rolling back, twice every day, they became alarrned, and attributed the phenomena to a special interposition of the deities of the country they had invaded. Various remarkable theories have been advanced regarding the tides. Maïly of these are truly so absurd that it is hardly worth while to refer to them. Persons flnd it difficult to understand why the tides are higher at one time than another, and why they rise totheheight of sixty f eet in the Bay of Fundy, forty in the ports of Bristol, England, and St. Malo, Prance, and only rise to a few feet in height at New York and other places, while they are scarcely perceptible in the Baltic and other seas. Descartes was the flrst philosopher who advanced the theory that the tides were due to the influence of the inoon, but Newton was the flrst who worked the problem and discovered the true cause. Descartes believed that the moon acted on the waters of the ocean by pressure; Newton demonstrated that it acted on the ocean by attraction; that instead of pressing on the waters, it rolled them up direetly under it, and alsoat its antipodes at the same time, thas producing the two tides every day. The tides are attractions of both sun and moon. If the earth had no moon, the attraction of the son would produce two tides every day, but their ebb and flow wouid take place at the same hours, ana not varying as they do. These tides would also be much smaller than those of the moon. Although the mass oL the snn is far greater than that of the moon, and though attraction is in proportion to the mass, yet it is also inversely as the square of the distance. As the sun, therefore, is four hundred times moredistant than the moon, the attraction of the waters of the sea toward the sun is found to be about three times less than that of the moon. There are reaUy two ocean tides, the lunar and solar, but the latter is absorbed by the former, which is wholly observable in respect to the time, the solar only as influences the height of the tidal wave. That caused by the moon, is three times greater than that of the sun, and it follows the moon's motion around the earth, rising and falling twelve hours, and each succeediug tidfc later by threequarters of an hour than the preceding one, is exactly in accordance with the position of the moon, or, as it is commonly called, its rising and setting.