TIDES

The alternate rising and falling of the surface of oceans, and of seas, gulfs, bays, rivers, and other water bodies caused by the gravitational attraction of the moon and sun occurring unequally on different parts of the earth. The tide ebbs (falls) and flows (rises) twice in each lunar day (24 hours and 51 minutes). It is occasioned by the attraction of the sun and the moon (the tide-raising force 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. High tide upon one side of the earth (Direct Tide) is accompanied by high tide upon the other side (Opposite Tide). Therefore, when the sun and the moon are in conjunction or opposition, as at the new moon and the full moon, their combined action produces a tide greater than usual, called Spring Tide. When the moon is at first or third quarter, the sun's attraction in part counteracts the moon's, causing a smaller high tide than usual (and a higher low tide), called Neap Tide. The flow or rising of the water is called Flood Tide; the reflux, Ebb Tide. Also see Spring Tide and Neap Tide.