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The alternate rising and falling of the waters of the
ocean, and of bays, rivers, etc., connected therewith. The tide ebbs
and flows twice in each lunar day, or the space of a little more than
twenty-four hours. It is occasioned by the attraction of the sun and
moon (the influence of the latter being three times that of the
former), acting unequally on the waters in different parts of the
earth, thus disturbing their equilibrium. A high tide upon one side of
the earth is accompanied by a high tide upon the opposite side. Hence,
when the sun and moon are in conjunction or opposition, as at new moon
and full moon, their action is such as to produce a greater than the
usual tide, called the spring tide, as represented in the cut. When the
moon is in the first or third quarter, the sun's attraction in part
counteracts the effect of the moon's attraction, thus producing under
the moon a smaller tide than usual, called the neap tide. |