Toward the outward margin of the storm or remote from the center of its path, the gale becomes less severe and the changes of wind more gradual and less hazardous. The navigator should so lay his ship, therefore, as to avoid the heart of the storm, and at the same time, to take the changes of wind which are to follow in the most favorable manner.

It will be found more difficult to form a just estimate of the direction and changes of the approaching gale in the latitudes near the outward borders of the trade winds and thence to 31° or 32°, than in other latitudes; for here the storm is rapidly changing its course, and the changes of wind cannot therefore be so accurately estimated.

MSS

NE

wind N

In south latitudes the course of storms is found to be in the reverse order to those which are traced on the chart; their progress being northwesterly in the intertropical latitudes, while on approaching the latitude of 30° south, they recurve towards the south and southeast. The rotary motion of the gale is also in the opposite direction from that which is found in the northern hemisphere, being to the E right, around the moving axis of rotation, as is shown in the annexed diagram for south latitude. The indicator C, here shows the storm as moving southwesterly, and a gradual change, by south, to southeast, will show the various directions and changes which pertain to the progress of the storm in different south latitudes.

ENE

wind N

wind NE

ESE

SE

Diagram for south latitude.

When the course of a ship at the commencement of a gale, is found to be across the track of the storm, the direction as well as force of the gale may be greatly affected by this gradual change of position. These changes of wind, as well as those to which a stationary vessel would be exposed, by the onward movement of the storm, may be understood by consulting the chart and diagrams: the latter, for the sake of convenience, may be drawn on a card and used upon the common charts.

If a ship is hove too and no attempt made to avoid the heart of the storm, it is apparent that her exposure may greatly depend upon the tack on which she is laid. This was strikingly exemplified in the Culloden's storm of March, 1809, in the Indian ocean, lat. 23° S. The Culloden, with a convoy of Indiamen, took the gale at SE. and the ships which were hove too with their heads to the southward were soon out of the gale, while those ships which stood on to the westward were either lost, or continued for a long time exposed to the full severity of the hurricane.*

It is owing probably, to the centrifugal action of these rotative storms, that the barometer always sinks under the first portion and towards the center of the storm, in all latitudes; and this fall of the barometer commonly affords the earliest and surest indication of the approaching tempest. When the center or axis of the storm has passed, the barometer commences rising, whether the wind has already been violent or not, and in some positions, as off the Cape of Good Hope, the last part of the storm with a rising barometer, usually exhibits the greatest violence of wind. The state of the barometer should always be recorded at regular and frequent intervals, in the log book or journal.

Observations on the duration and strength of the wind and the movements of the barometer on opposite sides of a storm have shown that in most cases the rotary action of the wind is not entirely uniform in its development; although the characteristic movements of rotation are clearly distinguishable. The rotation appears to be manifested most equally in storms which are distinguished for their activity and violence. Humboldt estimates the extreme velocity of the tropical tornadoes at two or three hundred miles an hour. The velocity of a heavy gale is from 60 to 100 miles. Colonel Beaufoy states that wind has only the 666th part of the effect of water, when moving with equal velocity. He observes also, that it frequently happens in violent storms of wind the current does not reach any considerable altitude; for often at the height of 1,600 feet, there is a perfect calm; on the contrary, it is not uncommon for the wind at considerable elevations above the level of the sea, to move with very great celerity, whilst the lower parts of the atmosphere remain in a state of tranquility.

* See Reid on the Law of Storms: London, 1838, p. 158-215.

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