The researches of Col. Reid, the Governor of the Bermudas, have likewise shown, that the storms and tempests of the southern latitudes are vast whirlwinds; moving, however, in a different manner from the hurricanes of the northern hemisphere. Thus, south of the equator, the general course of the hurricanes is from the northeast to the south-west, within the southern tropic; but after passing this limit they proceed from the north-west to the southeast; revolving from left to right, in the same way as the sun; a fact previously conjectured by Mr. Redfield. (See fig. 8.)

The hurricanes of the southern

Fig 8.

Southern Tropic

TION OF HURRICANES IN THE
SOUTHERN HEMISPHERE.

hemisphere frequently occur in GENERAL DIRECTION AND ROTA the vicinity of Mauritius and Madagascar.

The distance traversed

121. PATH OF THE STORM. by these desolating tempests is immense. The memorable gale of August, 1830, which fell upon St. Thomas, in the West Indies, on the 12th, reached the Banks of Newfoundland on the 19th; having traveled more than three thousand nautical miles in seven days; and the observed track of the Cuba hurricane of 1844 was but little inferior in length.

122. VELOCITY. Their progressive velocity varies on the Atlantic Ocean, from seventeen to thirty miles per hour; but at certain portions of the track it is sometimes much higher; as in the case of the Cuba hurricane, where the

State Col. Reid's views in respect to those of the southern.
What is said of the distance traversed by hurricanes?
What of their progressive and rotary velocity?

average rate from the Bahamas to 45° N. Lat. was forty miles per hour. Distinct from the progressive is the rotary velocity, which increases from the exterior boundary to the centre of the storm, near which point the tempest rages with terrific force; the wind sometimes blowing at the rate of one hundred miles per hour.

123. DIAMETER. The surface simultaneously swept by these tremendous whirlwinds is a vast circle, varying from one hundred to five hundred miles in diameter; but even the greatest of these dimensions was exceeded in the Cuba hurricane, for its breadth was computed by Mr. Redfield to be at least 800 miles, and the area over which it prevailed, throughout its whole length, 2,400,000 square miles; an extent of surface equal to two-thirds of that of all Europe.

124. The rotary character of the hurricane accounts for the frequent changes that occur in the direction of the wind; since, in order to preserve a circular motion, there must be a constant deflection from a straight course, and, at corresponding points in each half of the storm, the gale will blow from opposite quarters. The changes thus caused, will be perceived at any spot over which this fearful visitant passes.

It also explains the fact, that the violence of the wind increases towards the centre, and that, within the very vortex of the hurricane, the air is in repose. Here occurs that awful calm, described by mariners as the lull of the tempest, in which it seems to sleep, only to gather strength for mightier conflicts.

125. CASES. Numerous instances of the facts above mentioned might be adduced, but one or two will suffice. In the Antigua hurricane of 1837, described by Col. Reid, it appears that Capt. Newby of the Water Witch, first experienced its effects at St. Thomas, in the West Indies, on the morning of the second of August. The wind was then N. N. W., and at three in the afternoon

How great is their breadth?

How great the surface over which they prevail?

What facts are explained by the rotation of the storm?

Give instances.

became violent. At five P. M. it blew a severe gale, and at seven P. M., says Capt. Newby, "a hurricane arose beyond description dreadful. Soon after a calm succeeded for about ten minutes, and then, in the most tremendous screech I ever heard, it recommenced from the S. and S. W. At two o'clock on the morning of the third, the gale somewhat abated, and the barometer rose an inch. At daylight, out of forty vessels, the Water Witch and one other were the only two not sunk, ashore, or capsized."

126. On the 12th of August, 1837, another hurricane commenced, in the same region, in 17° N. Lat. and 53° 45' W. Lon. At midnight on the 18th, in 31° N. Lat., the ship Rawlin, Capt. Macqueen, appears, according to Col. Reid, to have been in the very vortex of the storm. On the 17th, the wind blew strong from the N. E. by E. for twelve hours, then suddenly changed to the north, blowing with undiminished violence till the 18th at midnight when, in an instant, a perfect calm ensued for the space of one hour; then, "quick as thought, the hurricane sprung up with tremendous force from the S. W.; no premonitory swell of the wind preceding the convul-. sion." During the gale, the barometer was almost invisible in the tube above the framework of the instrument.

The sudden and extraordinary transition detailed in the cases just cited, are fully explained by supposing, that the vessels passed from one side of the whirl to the other, through the vortex of the tempest.

127. FALL OF THE BAROMETER. If the hurricane is indeed a vast whirlwind, the atmosphere, constituting the body of the storm, will be driven outward from the centre towards the margin (C. 171), just as water in a pail, which is made to revolve rapidly, flies from the centre, and swells up the sides. But the pressure of the atmosphere, beyond the whirl, checking, and resisting this centrifugal force, at length arrests the outward progress of the aërial particles, and limits the storm.

If the hurricane is a whirlwind, in what manner should the barometer fall and rise?

We should consequently expect to find (in accordance with the laws of circular motion) the density of the air increasing from the centre to the circumference of the storm, and even for some distance beyond its boundary; and likewise, that when a hurricane passed diametrically over any region, the atmospheric pressure would decrease, and the barometer continue to sink, during the first half of the storm; but that the instrument would gradually rise, as the last half passed over. Such indeed is the case; for, amid all the phenomena of storms, no fact is better established than this, that an extraordinary depression of the barometer in tropical climates is a sure forerunner of a hurricane.

128. Before the tempest of Aug. 2d, 1837, the harbormaster of Porto Rico warned the shipping in port to prepare against a storm, as the barometer was falling in an unusual manner; having sunk one and a half inches since 8 o'clock in the evening of the preceding day. All precautions were however in vain; thirty-three vessels at anchor were destroyed, and, at St. Bartholomews, two hundred and fifty buildings levelled to the earth. The following table of observations, taken at St. Thomas, over which island this hurricane passed, is full of instruction in regard to this important point.

Is this the case? Relate the instances given.

130. In the case of the Water Witch, we have seen, that, when the centre of the tempest was past, and the gale abated, the barometer rose an inch.

131. CIRCUIT SAILING. The gyratory motion of hur ricanes is strikingly evinced by vessels sailing on a circular course, when scudding before the wind. The most remarkable case is that of the Charles Heddle, related by Mr. Piddington, which occurred in a storm, near Mauritius, in Feb. 1845.

It appears from the log-book of this ship, that, in her course before the gale the wind changed completely

What example is given of circuit sailing?