Abbildungen der Seite
PDF
EPUB

voyages to foreign countries. He is seldom in debt. His house is well painted and carpeted, and every thing is comfortable and in good repair. His children are at academies or colleges, and he is a prudent, moral, and temperate man ; and could we induce him to leave off whittling shingles, and the immoderate use of tobacco, he is so gentlemanly, that he might sometimes be mistaken for the captain of “a New York liner."

Art. IV.-1. Various Papers on Meteorology, and the Laws

of Storms, by W. C. REDFIELD. American Journal of Science and Arts, Vols. XX, XXV, XXVIII, XXXI, XXXIII. Jamieson's Edinburgh Journal for February and April, 1838. Naval Magazine, Vol. I. English Nautical Magazine,

1839. Journal of the Franklin Institute, Vol. XIX. Blunt's Coast Pilot, 12th and

13th Editions. 2. An Attempt to develope the Law of Storms by Means of

Facts, arranged according to place and Time, and hence to point out a Cause for the Variable Winds, with a View to practical Use in Navigation. Illustrated by Charts and Wood Cuts. 2d Edition, with Additions. By Lieut. COLONEL W. Reid, C. B., F. R. S., (of

the Royal Engineers.) London. 8vo. 3. The Philosophy of Storms. By James P. Espy,

A.M., Member of the American Philosophical Society, and Corresponding Member of the National Institute,

Washington. Boston : 1841. 8vo. 4. On the Storm which was experienced throughout the

United States about the 20th of December, 1836. By
Elias LOOMIS, Professor of Mathematics and Natural
Philosophy in Western Reserve College. Philadelphia :
Phil. Trans., Vol. VII., New Series.

About a century ago, Dr. Franklin made preparations to observe an eclipse of the moon at Philadelphia. The execution of his purpose was prevented by a storm from the north and east, which obscured the sky a short time before the moon passed into the earth's shadow. He learned afterwards, to his surprise, that this eclipse had been seen at Boston; and upon comparing the accounts from the other Colonies, he discovered, that our northeast storms obey a fixed law of progress; that they are experienced first in the southwest, and advance towards the northeast. *

The study of this law has led to a series of discoveries in the science of meteorology of the highest value, whether regarded as contributions to knowledge, or as the basis of useful rules for the guidance of conduct ; from which the practical man may derive great advantage, and which the philosopher with honorable pride may number among those benefits which his patient investigations confer upon mankind. 66 Tant est féconde la méditation d'une loi de la nature." These discoveries relate chiefly to the phenomena of storms, — of those dreadful hurricanes especially, which vent their first fury upon the fertile islands of the Caribbean sea, where they originate, and passing thence to the continent, strew the shores of the United States with the wrecks of our rich commerce. By a laborious collation and careful comparison of scattered records, our countryman, Mr. Redfield, obtained a knowledge of their principal features, and consummated his task by the discovery of the general fact, that these storms are comparatively isolated masses of air in a highly disturbed state, the particles of which revolve with such violence as to create the destroying winds called tempests, or hurricanes. Thus the Preacher, in illustrating the vanity of all human pursuits, uttered the language of a correct philosophy. “The wind goeth toward the south, and turneth about unto the north ; it whirleth about continually, and the wind returneth again according to his circuits.”

The first suggestion, that a storm might be a great whirlwind, was made by Colonel James Capper, of the East India Company's service, in a work on the winds and monsoons of India, published in 1801. He points out the method of investigation since adopted by Mr. Redfield, to whom, however, Colonel Capper's book was entirely unknown. Indeed, this book seems to have attracted little notice before Mr. Redfield's discovery. About the time that the American philosopher was employed in his earlier, labors of observing and collecting the observations of others, a similar inquiry was in progress in Germany. On Christmas eve, 1821, after a long continuance of stormy weather, the barometer sank so low in Europe, that the attention of meteorologists was strongly drawn to the circumstance, M. Brande, having obtained the registers kept at this time in various places, came to the conclusion, that, during this storm, the winds blew from all points of the compass towards a central space, where the barometer was, for the moment, at its lowest stand. This conclusion was disputed by Professor Dove, of Berlin, who subjected the observations in the possession of Brande, as well as others, to a new examination, and made it appear, that an explanation of all the phenomena was afforded by the assumption of one or more great rotary currents, or whirlwinds, advancing from the southwest to the northeast. * Before this discussion was known in the United States, Mr. Redfield, by an independent course of investigation, had arrived at the result we have already announced, and his opinion is fortified by facts and cases so numerous and well authenticated, as fully to justify the distinction which Sir David Brewster has accorded to him in the following language. “The theory of rotary storms was first suggested by Colonel Capper ; but we must claim for Mr. Redfield the greater honor of having fully investigated the subject, and apparently established the theory upon an impregnable basis.”+

* This eclipse occurred on the 21st of October, 1743. See an Attempt to fix the Date of Dr. Franklin's Observations in Relation to the North-East Storms of the Atlantic States," by A. D. Bache. Franklin Journal for November, 1833.

An inquiry into the nature and operation of these mighty agents of destruction, the sweeping storms on the sea, or the ravaging tornadoes on the land, will prove not less an advantage to humanity than to science. To be able to foretell their approach, and to know their course and action, is to warn the farmer and mariner in time to guard against their effects. And science will be acknowledged to fulfil one of her highest aims, when she adds to those instructions which direct the course of the adventurous seaman over the ocean, the knowledge that will protect him against the rebellions violence of the tributary elements.

Mr. Redfield's researches have made us acquainted with the following general laws. The winds in a great storm, which were once supposed to travel in a direct path pointed

* London and Edinburgh Journal of Science, Nos. 67, 68. + Philosophical Magazine, Vol. XVIII., 3d Series, p. 515.

out by the vane, do actually revolve about a vertical line or space, which may be regarded as the central axis of motion. Professor Leslie framed a theory accounting for the barometric fluctuations, according to which, the winds in hurricanes were presumed to move in a rectilinear direction, at the rate of one hundred or one hundred and twenty miles an hour. Mr. Redfield has shown, however, that a storm is no longer to be considered as the unequal disturbance of an extended stratum of the atmosphere, but as a vast whirlwind, or vortex, approaching to a cylindrical form, throughout which the motion of the air is rotary. It is not one wind, but a combination of winds from all quarters.

“ Una Eurusque, Notusque ruunt, creberque procellis

Africus," These whirlwinds, or aērial vortices, have a progressive movement, that carries forward the whole body of the storm, apart from the internal motions, which cause its violence. This progressive movement depends upon the prevailing currents of the upper air, and varies from twelve to thirty miles an hour. Such, at least, is the rate of progress of those storms examined by Mr. Redfield. He is aware, however, that some storms appear to be local, and nearly stationary, whilst others move with greater rapidity.

The rotation of the air in the body of the storm is, on the north side of the equator, from the right to the left, or contrary to the movement of the hands of a watch; and, in southern latitudes, from the left to the right, or with the hands of a watch. Its violence increases towards the interior ; but in the centre is a space where the winds seem to lose their force. This calm in the middle of a heavy storm is well known to seamen, as the forerunner of a dangerous and violent shift of wind. The barometrical changes first noticed by Mr. Redfield are remarkable, and serve to indicate to the observer the portion of the storm that he occupies. The arrival of the storm, as is well known, is preceded by a fall of the mercury. Mr. Redfield has found, that this fall increases as the storm passes over, up to the central space,

where it attains its maximum; the barometer then begins to rise, and gradually mounts as the latter section of the storm recedes. These changes, which are proofs of a rotary and progressive movement, are very valuable to seamen, particularly in pointing out the central calm,

the deceitful character of which has, no doubt, caused the wreck of many vessels. The extent of the storm, or of the region over which its influence is felt, Mr. Redfield believes to vary from one hundred to five hundred miles.

Those which originate in the tropics increase in diameter, and diminish in violence, as they proceed towards the poles ; and it is suggested by Colonel Reid, that the gales become huddled together as the meridians approach each other, and are so complicated in high latitudes by their rapid succession, that it is not easy, during the season of storms, to identify a particular one.

Mr. Redfield's attention was first called to the hurricanes of the West Indies, the fatal visitations of which are so well and mournfully recorded in the shipping lists.* Availing himself of the various sources of information, he was enabled to pursue the track of a storm from the place of its first appearance, to some point far to the east in the North Atlantic ocean, where its forces, like those of the Gulf Stream, were weakened by diffusion. The charts of the hurricanes show, that they take their rise in the vicinity of the Windward islands, and proceed in a northwesterly course, until they approach the continent of America, where, between the twenty-fifth and thirty-fifth degrees of latitude, they change their path to the north and east, inclining gradually to the east. Their course then becomes nearly parallel to the coast, and sometimes their influence is felt on the whole Atlantic shore, from Cape Florida to Halifax.

One of the hurricanes of August, 1830, has been traced by Mr. Redfield in its daily progress, by means of the journals and reports

of voyagers, from near the Caribbee islands to the coast of Florida and the Carolinas, and thence to the banks of Newfoundland, a distance of more than three thousand miles, which was passed over by the storm in six days, at the rate of about twenty-one miles an hour. The duration of the most violent portion of this gale, at the different points over which it passed, was about twelve hours ; but its entire duration was, in some places, twice that period. The

* The West India hurricane season is reckoned from the 15th of July to the 15th of October. During this period, premiums of insurance, that are usually 24 per cent., rise to 4, and 6 per cent. The hurricane region is. included between the 10th and 20th degrees of north latitude, and the 58th and 86th degrees of west longitude. VOL. LVIII. No. 123.

41

« ZurückWeiter »