of the desert. Clouds of glowing sand, at times so thick that objects are invisible at the distance of a few paces, are driven with blinding force against the face; the moisture is rapidly absorbed from the body, the skin becomes parched, the throat inflamed, respiration is accelerated, and a raging thirst created. And in the midst of these horrors, the burning blast deprives its unhappy victims of the only means which they possess for alleviating their sufferings; the water evaporates through the skins in which it is carried, and whole caravans have been known to perish, the prey of a consuming thirst.

117. SIROCCO. This name is given to a south-east wind which prevails in the Mediterranean isles, and along the Italian shores. During the summer and autumn it is peculiarly distressing to the inhabitants of these regions; an oppressive sensation of heat is then felt, the skin is bathed in perspiration, the body becomes weak and languid, and the mind dispirited. These effects are attributed to the fact, that the sirocco, at this time, is both hot and moist; very little evaporation therefore occurs, and the sensations experienced, under these circumstances, are similar to those which are felt during a very sultry state of the atmosphere. While this wind prevails, the air is obscured by fine particles of dust, and is always hazy.

The sirocco has been generally supposed to arise from a current of air flowing across the Mediterranean from the glowing sands of Africa. It acquires its heat from the desert, and its moisture from the sea.

CHAPTER II.

OF HURRICANES.

118. HURRICANES are terrific storms, accompanied, at times, by thunder and lightning; and differ from

Describe its effects. Describe the Sirocco.

What does chapter second treat of? What are hurricanes ?

every other kind of tempest by their extent, their irresistible power, and the sudden changes that occur in the direction of the wind. Though known in other climes, they rage with the greatest fury in the tropical regions The rich products of the plantations are destroyed in a moment, forests are leveled, the firmest edifices prostrated and their roofs whirled aloft into the air, which is filled with the flying fragments of a thousand ruins. Upon the coasts, the waves rush landward with appalling violence, lining the harbors and the adjacent shores with the cargoes and wrecks of shattered vessels.

Fig. 7.

119. From the late independent investigations of several eminent philosophers, it also appears that hurricanes are extensive storms of wind, which revolve around an axis, either upright or inclined to the horizon; while at the same time, the body of the storm has a progressive motion over the surface of the globe.

120. We learn from the numerous observations collected by Mr. Redfield, of New York, that in the northern hemisphere, the Atlantic hurricanes generally originate to the east of the Carribean islands, and that their path is from southeast to north-west, until they have passed the northern tropic, when their course changes from south-west to north-east; the rotation of the storm being from right to left, contrary to the

Northern Tropic

S

motion of the sun, (see fig. 7., GENERAL DIRECTION AND ROTAwhere the arrows show the di- TION OF HURRICANES IN THE rection of the wind.)

NORTHERN HEMISPHERE.

Where are they most violent? What do many philosophers now consider them to be?

State Mr. Redfield's views in regard to the Atlantic hurricanes of the northern hemisphere.

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 hemisphere frequently occur in the vicinity of Mauritius and Madagascar.

Fig 8.

N

Southern Tropic

S

GENERAL DIRECTION AND ROTA-
TION OF HURRICANES IN THE
SOUTHERN HEMISPHERE.

121. PATH OF THE STORM. The distance traversed 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 convulsion." 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?