Page:The ocean and its wonders.djvu/52

 in foam, and the ocean in a few minutes presents the appearance of a caldron of boiling milk! Such squalls are extremely dangerous to mariners, and vessels exposed to them are often thrown on their, even though all sail has been previously taken in. Generally speaking, however, the immediate effect of wind passing either lightly or furiously over the sea is to raise its surface into waves. But these waves, however large they may be, do not affect the waters of the ocean more than a few yards below its surface. The water below their influence is comparatively calm, being affected only by ocean currents.

The tides of the sea—as the two great flowings



and ebbings of the water every hours are called—are caused principally by the attractive