Tho diagram, therefore, may be regarded as a plan or a horizontal section, or, more accurately, a section at right angles to the axis, of a revolving storm. In the sequel of this article another diagram will be found, presenting vertical sections of such storms, or sections parallel to their axis, and at right angles to their greatest diameter.
The hurricanes or whirlwinds of the Atlantic commence in a part of the ocean which is frequently designated the region of variable winds, and is situated between 10' and 20' N. lat., and between 55° and 60 W. long., and their progress along the coast of the United States is marked by the devastation they so often produce. They are felt between July and October, but they arc most frequent and violent in August and September ; and being on the great line of communication between Europe and the West, the phenomena which they present have been more attentively observed than those of the storms in any other region of the earth. The valuable publications of 3Ir. ltedfield contain nearly all the details which have yet been collected concerning them ; while the works of the into Sir W. Reid [REID, Sra Wthr rcM, iu Moo. Div.], especially that entitled An Attempt to develope the Law of Storms,' contain almost all that is known of the whirlwinds in the southern hemisphere.
In the ' American Journal of Science,' vol. xx., it is shown that the storm which took place in September, 1821, began in the West Indies, and arrived off the coast of the United States, in lat. 35° N., at day light, September 3rd, when the wind blew from E.S.E. On the same day, at 11 a.m., the storm commenced at Cape Henlopen, with the wind in the same quarter, but it afterwards shifted to E.N.E., and blew during nearly an hour : a calm of half an hour succeeded, when the wind shifted to W.N.W., and blew with great violence. At New York the storm commenced at 5 P.M., from E. and N.E., the wind blowing with fury for three hours, and then it changed to W. At Boston the hurricane commenced at 10 P.m., but beyond this city it was not traced. All the phenomena just mentioned indicate, agreeably to the principles above explained. a revolving hurricane in which the direction of the rotation was according to the order of the cardinal points, N., W.. S., E., while the progressive movement of the axis was about N. by E. The temporary calm at Cape Henlopen seems to show that the centre of the vortex was then near that place.
In the same work it is stated that, during the hurricane of 1830, at the Bahama Islands, the wind veered almost round the compass in the night of August 14. The storm appears to have passed from the island of St. Thomas, near Porto Rico, to the south-east coast of Nova Scotia, in about six days, consequently it must have moved at the rate of about 17 miles per hour ; and by the positions of the different points at which its effects were at the same time felt, its diameter must have been about 150 or 200 miles.
A movement of progression combined with a movement of rotation in the direction of the points N., W., S., E., is also indicated by the phenomena of the Barbadoes hurricane in August, 1831, in July, 1837, and of the hurricane nt Antigua, August 2 of the latter year. But of the North Atlantic storms, that which presents the most remarkable phenomena is one which raged between the 12th and 23rd of August, 1637. Details of the circumstances attending it have been given at length, with a chart of its coarse, by Sir W. Reld, in his work on
storms ; and it appears that it was first felt in lat. 17' 30'N., about 400 miles eastward of Antigua, though it may have had its origin still farther eastward.
By the effects experienced at different points on the ocean, Sir W. Reid concludes that the centre or axis of the storm advanced at first from east to west nearly ; and after moving in that direction about two days, it turned towards the north-west, as if the storm had been abruptly deflected from the land ; and when the whirlwind ceased to he noticed, it was passing eastward across the Atlantic to the south of Newfoundland. On the 18th of August, 1837, a ship, named the Rawlins, was becalmed for an hour in lat. 30° 30' N. nearly ; at that time another, named the Calypso, above three degrees northward of the Rawlina, was thrown on her beam-ends with the wind successively at N.W., W., and S.W.; and a ship, named the Sophia, situated about as far towards the north-east of the Rawlins, evidently eastward of the storm's centre, experienced the hurricane from the E.N.E., E., and E.S.E. Previously to the temporary calm, the wind at the place of the Rawlins had been N.E. by E. and N., and afterwards it suddenly changed to the S.W. These circumstances sufficiently indicate that the whirlwind had then a progreasive motion towards the north-west, and at the same time a rotation in the direction of the points N., W., S., E. On the 20th of August the wind at the point occupied by the Sophia appeared to veer back, first to the east, and subsequently to the north ; and since at this time the progressive movement of the hurri cane had changed from a south-west to a north-east direction, the veering of the wind admits of being explained on the supposition that the Sophia had then fallen into the western semicircle of the whirlwind, while the latter, still revolving in the same direction, passed over her.
That independent whirlwinds occasionally interfere with each other may be inferred from the circumstances attending the voyage of the Castries from St. Lucia to England in the same year (1837). This ship, between the 14th and 25th of August, sailed nearly from south to north on the chord of the arc described by the centre of the great hurricane just mentioned. On the 14th and 15th, in about the 18th degree of north latitude, where the wind usually blows from the east, she felt a gale, which at first came from 3.3.1V., and afterwards changed to S.E., as if she had crossed the eastern side of a storm revolving in the direction N., W., S., E., and whose centre was moving nearly from east to west : this was in fact the said hurricane near the place where it was first observed. The Castries then sailed northward with fair weather till August 24th, when, in lat. 35° 46' N. and in long. 57' 40' W. nearly, she was overtaken by a whirlwind which paned over her. Now this could not have been the great hurricane before mentioned, since at that time the latter had passed beyond the spot towards the N.E., and the rotation at its southern extremity must have caused at the place a west wind to be felt ; whereas the direction of the wind at the ship was at first from E.S.E., subsequently changing to N.E., N., and N.W. : the ship must evidently therefore' have been then In the north-eastern. side of a whirlwind coming np from the S.E., and revolving, like the others, in the direction