Page:Physical Geography of the Sea and its Meteorology.djvu/449

Rh against the hands of a watch; but when the wind is north, it is, in the case supposed, travelling south at the rate of 20 miles an hour around the storm, while the progressive movement of the storm itself is north at the rate of 20 miles an hour. One motion exactly cancels the other, and there is, therefore, a line of calm and light, or moderate or not so heavy winds on one side of the centre, while on the other side there is a line of maximum violence; in other words, in every travelling cyclone the wind blows harder on one side than the other. This is the case in both hemispheres; and by handling these moving diagrams for illustration, the navigator will soon become familiar with the various problems for determining theoretically the direction of the vortex, the course it is travelling, its distance, etc. Therefore, when it is optional with the navigator to pass the storm on either side, he should avoid the heavy side. These remarks apply to both hemispheres.

793. The rainy quadrant of a cyclone. Captain Toynbee asks if it rains more in one quarter of a cyclone than another? In cyclones that travel fast, I suppose there would be most rain in the after quarter; with those that have little or no progressive motion, I conjecture that the rainy quarter, if there be one, would depend upon the quarter whence that wind comes that brings most rain. The rain in a "cyclone is supposed to come from the moisture of that air which has blown its round and gone up in the vortex; then it expands, grows cool, and condenses its vapour, which spreads out at top like a great mushroom in the air, the liberated heat adding fury to the storm.

794. Erroneous theories.—Such, briefly stated, are the two theories. They appear to me, from such observation and study as I have been able to bestow, to be neither of them wholly right or altogether wrong. Both are instructive, and the suggestions of one will, in many instances, throw light upon the facts of the other. That rotary storms do frequently occur at sea we know, for vessels have sometimes, while scudding before the wind in them, sailed round and round. The United States brig "Perry" did this a few years ago in the West Indies; and so did the "Charles Heddle" in the East Indies: she went round and round a cyclone five times.

795. The wind in a true cyclone blows in spirals.—From such observations as I have been able to obtain upon the subject, I am induced to believe, with Thorn, that the wind in a cyclone does