Page:Physical Geography of the Sea and its Meteorology.djvu/299

Rh most simple plan for determining the velocity of waves—and it may be hourly practised on board of every vessel—is the plan which is followed by Captain Ginn, of the American ship John Knox, one of our co-operators. When he heaves the log with the 8eas following, instead of hauling in the line immediately, he leaves the chip to tow, watching till he observes it on the crest of a wave; he then turns the glass, or notes his watch, and marks the time it takes the wave to reach the ship. The usual velocity of the waves in the Atlantic is 22-3 miles an hour, off Cape Horn 26-8.

508. Determining the height of clouds at sea.—It would afford a pleasant and agreeable diversion for a squadron of men-of-war, as they pursue their voyage at sea, to amuse themselves and instruct their friends at home with observations upon all such phenomena. Those who are willing to undertake the clouds will have no difficulty in devising a plan both for the upper and the lower strata.

509. Cloud region at sea in the shape of a double inclined plane.—Over the land the cloud region is thought to vary from three to five miles in height; there the height of clouds is known to be very variable. At sea it is no doubt less so. Here the cloud region is somewhat in the form of a double inclined plane, stretching north and south from the equatorial cloud-ring as a sort of ridge-pole. In the balloon ascents which have taken