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.[1]
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
- ↑ From Captain Ginn's Abstract Log:—"Saturday, September 11th, 1858, doubling Cape Horn. The long regular swell during this part of the day afforded me another opportunity of trying the velocity of the waves. This I did by paying out the log-line enough to be equal to 13 knots with the 14r-second glass; then by watching the chip—to which I had fixed a piece of white rag to render it more distinguishable—as it appeared on the crest of a well-defined wave, and turning the glass at the same time, and then noting where the crest of a wave is at the moment the glass is 'out.' "I have several times before tried the experiment in this way with the same length of line out astern, and have always found about the same rate for the velocity, namely, 22 to 23 miles an hour; but to-day I found it to be considerably more, namely, 26 to 28 miles an hour. Thus the crest of a wave would pass, while the 14-second glass ran out, from the place where the log-chip was towing astern (13 knots) to just ahead of the ship. The length of the ship is equal to about 6½ knots: the ship's speed at the time was 8 knots; thus, 13+6½+8 = 27½. A few days ago I tried the same experiment, and found the velocity to be 22 to 23. What has accelerated the velocity of these waves? Have the soundings anything to do with it?"
