2. A fitful variation of intensity in the force of the wind, which sometimes blows with fearful violence, carrying away everything that opposes its progress; then sinking to a gentle breeze, or even lulling to a calm, but almost immediately afterwards springing up with greater violence than before. The hurricane winds are nearly if not entirely, without exception, puffy, violent, and blowing in gusts.
3. An immense condensation of aqueous vapor, forming large banks of cloud, which precipitate torrents of rain. The condensation appears to be so exceedingly rapid that large quantities of electricity are generally developed, giving rise to incessant flashes of lightning.
4. A general darkness, and gloominess within the area of the cyclone, relieved only by the fitful glare of the lightning, or the appearance of the imperfect circle of light near the center or axis of the storm.
5. A separation of the clouds in or near the center of the hurricane, so as to produce in the immediate neighborhood of the axis a clear sky, through which the sun and stars are often seen with great brilliancy.
6. A calm in the center of the cyclone.
INDICATIONS OF APPROACHING OR EXISTING
HURRICANES, MANIFESTED BY THE OCEAN,
OF ESPECIAL UTILITY TO VESSELS AT
ANCHOR IN ROADSTEADS.
1. A swell, produced by the storm-wave, rolling in upon the shore, at first of a gentle character. The direction of this swell will pretty surely indicate the bearing of the storm, and its changes will point out in some localities the course the hurricane may be pursuing.
2. A swell rolling in, without changing its direction, may be regarded as indicative of a hurricane approaching the shore. The same phenomenon met with at sea (the ship’s course being taken into account) will indicate the bearing down of the cyclone on the vessel.
3. A dirty green appearance of the ocean; on some occasions its assuming a muddy or brown color, on others its being remarkably clear, its temperature increasing, and its swellings stronger than at other times,—are all indications of the proximity of a cyclone.
The area over which these rotary storms have been known to expand, varies from 30 to 40 to 1,000 miles; but while the diameter, so long as the storm is within the tropics, expands but very gradually, it suddenly increases in a remarkable manner after recurving. The rate at which they travel on their onward course also varies greatly, not only in different parts of the globe, but even in the same locality, and at the same season. Generally, however, the rapidity with which the vortex of the hurricane progresses is greater as the storm recurves on reaching the outer edge of the trade winds. Thus, the hurricane of August, 1853, traversed 6,276 English miles in about twelve days, with a mean progressive velocity of twenty-six miles per hour; but after it arrived at the Banks of Newfoundland this velocity was increased to about fifty miles per hour.