Imágenes de páginas

These experiments were more striking than was anticipated, but were prosecuted under difficulties which prevented their being completed.

They are intended as the preliminaries to more extended and complete investigations in the same direction, to be continued at some future time, embracing the interesting question, whether tendrils are influenced by the same causes and follow the same law, also some things relating to the direction of winding plants, the length of their spirals compared with their diameter, the di. rection of the spiral growth of various trees, &c. Some observations have already been made on all of these subjects except that of tendrils.

The experiments performed, indicate, I think,

1st. That during the day winding plants like others grow towards the light.

2d. That they possess the property of turning towards some solid support.

3d. That this is more manifest by night than by day, and the most so on cool nights following hot days.

4th. That this is not controlled by any influence of light or its absence, exerted by the support.

5th. That heat is the controlling cause, and that such plants will only turn (unless it be accidentally) towards a support, the temperature of which is higher than that of the surrounding air.

6th. That the color and material of the support exert no influence further than that they influence the radiation and absorption of heat; and

7th. That when such plants are in actual contact with some support, the tendency to wind spirally around it is much greater than they manifested in order to reach it.

Art. XXV.-On some Anomalies in the Florida Gulf Stream,

and on their further Investigation; by Lieut. E. B. HUNT, Corps of Engineers, U. S. A. (Read before the American Association for the Advancement of Science, at

the Baltimore Meeting, May, 1858.) THERE is perhaps no portion of the ocean waters which has been so imperfectly studied, in proportion to its importance, as that from the west end of Cuba through the Gulf of Florida. The whole commerce of the Gulf of Mexico is directly concerned in whatever investigations shall more accurately define the currents or other physical peculiarities of that portion of the Gulf Stream area from the line joining Cape Antonio to Cape Catoche, and the latter with the Tortugas, thence to the eastward through that grand channel bounded on the north and

west by the Florida Reef and mainland, and on the south and east by Cuba and the Bahama banks. As it is the natural outlet for the products of the entire gulf coast and of the valley of the Mississippi, the present commerce following this route, vast as it is, must ultimately be so far exceeded, that it will seem almost insignificant in comparison with that which another half century will direct through this channel. The character of this navigation, no less than its amount, is such as to demand the most careful study of the currents, by which it is so largely influenced. All are so familiar with the immense annual losses to commerce by wrecks and disasters on the Florida Reefs and Bahama Banks, that a simple reference to the fact will abundantly vindicate the importance of carefully gathering whatever knowledge can give greater safety to this navigation. The high extra premiums for marine insurance by this Florida channel route, afford another striking testimony to the risks of this navigation; but I think it right to remark here, that, from the best information I could obtain at Key West, the Florida channel insurance rates are very much too high, and are annually giving exorbitant profits to the insurance companies. This makes it the interest of these companies to exaggerate the dangers of this passage; and it is believed that they are, on this account, less averse to wrecks, and less strict in distinguishing collusive or fraudulent wrecks than they should be. A reduction of rates must soon be made, if we may judge from the fact that owners are, to a considerable extent, becoming their own insurers, in preference to paying the established rates. The new light-houses and coast-survey beacons have added much to the security of this route, and the business of wrecking at Key West is, on the whole, diminishing, although commerce is of course increasing. Making all due abatement for the exaggerations of the terrors of the Florida Straits, and for the increased aids to navigation, there still remains a very serious annual marine loss, due almost entirely to the imperfect acquaintance of navigators with the peculiarities of the route, and especially with the currents. MisIed by false or imperfect views about the Gulf Stream, and other currents prevailing here, sea captains are frequently so unfortunate as to run directly on the reefs, while they suppose they are well out in the channel way. I cannot but think that a system of reef pilotage, properly organized and well conducted, would lead to a great reduction in the number of casualties. By taking and leaving well-trained pilots at the entrance to, and exit from, the region of danger, the numerous casualties due to the imperfect knowledge of sea captains would be in great part obviated. Skillful pilots, constantly engaged in taking vessels through the channel, would grow more and more certain of all the essentials for secure passages, until it would become a gross offence to lose a vessel, except from causes truly extraordinary. It is obvious that such pilots should be so situated that no possible advantage could accrue to them in case of wreck, while a premium should be awarded for each safe pilotage. Were such a system in full operation, it would be a proper rule that a vessel failing to take a reef pilot should forfeit its insurance, ex. cept when no pilot could be procured. A great difficulty in accomplishing this plan except by the combined action of the insurance companies, is found in the fact that three national jurisdictions enter the field of pilotage.

A first essential for giving greater security to the Florida channel navigation is a more correct determination of the currents by which vessels are affected during the transit. Having spent the last winter at Key West, I was led to inquire about these currents with some particularity, and, as a result, was brought to the opinion that the prevalent views are very seriously at fault. There are many facts quite incompatible with the common notions of a vast current constantly sweeping around the Gulf of Mexico, and thence pouring in full volume through the Gulf of Florida. I will here cite some notes of tes. timony given me by various persons specially acquainted with the matters in view. They were questioned more particularly with reference to facts and opinions touching a southwesterly current prevailing more or less between the easterly Gulf Stream and the Florida reef. Such a counter or eddy current is definitely indicated on Jeffrey's map of 1794, by a dotted line, above which is written, “North of this line is a current setting southwestward, unless when the wind is at north or east, which winds admit of no southwest;" and, “South of this line the current of the Florida stream sets always northwardly.”

Capt. Geiger, who for over thirty years has been observing the waters of this vicinity, most of that time having acted as a pilot off Key West harbor, and who is perhaps better acquainted than any other person with the currents there prevailing, gives the following statement of facts.

A strong north or northeast wind keeps the Gulf Stream back, and makes a westerly current near the shore. During June, July, and August, the westerly current prevails more than the easterly current from five to fifteen miles from the reef. The direction of the current depends mostly on the wind. The westerly current prevails for from one third to two fifths the entire time from year to year, for from two to fifteen miles outside the reef off Key West. He has known it twenty-five to thirty miles off Sand Key. When the Gulf Stream is strongest on the Cuba shore, the westerly current is strongest on the north side; and when it is weakest along the Cuban shore, the Gulf Stream sets close along the reef. He has found the westerly current as

far up as Carysfort, but not frequently, and not broad or strong. This current broadens from Carysfort to the westward, and continues about constant along its course. The tides on the two sides of the reef are about six hours apart, on an average; but set, on the whole, as much one way as the other over the reef. Sometimes there is a narrow easterly current for a mile from the reef; then a westerly current, and then the Gulf Stream. Both the United States steamers Susquehanna and Wabash were set westwardly by the current about eight or ten miles during the past season. A considerable number of the Gulf traders know of the westerly current, and make more or less use of it in navi. gating westwardly. When running with the wind the water is smooth, and rough when running against it. After northers, the westerly current is to be expected. Sometimes, in crossing to Havana, no Gulf Stream indications are found; and sometimes a westerly current is found along the north shore of Cuba. Notwithstanding Capt. Geiger's long observation of these currents, he says that he is quite unable to reduce them to rule, or in any way to know before hand how the current will be found to set. He asserts that the Gulf Stream sets from the vicinity of Cape St. Antonio, northeasterly through the Florida channel, and that the main stream does not make the circuit of the Gulf of Mexico as generally supposed.

Captain Richardson, pilot of the Coast Survey surveying steamer Corwin, says, in substance, as follows: The westerly current appears irregularly chiefly in the winter, but sometimes during the prevalence of the regular trades. It extends from ten to fifteen miles off from Sand Key, sometimes running as much as two miles an hour. It never prevails over the reef proper. It sets for two months or so some winters. It spreads farther from the reef as it goes west. Has known it as far north as Carysfort, just outside the reef, and at Cape Florida even where the reef is narrow and deep, this current sometimes sets across it some two miles from shore, but is not very frequently found there. As it runs west it seems to increase in breadth. Off Indian Key he has known it to extend seven miles from the edge of the reef; at Bahia Honda it is sometimes ten miles, and at Sand Key, from ten to fifteen miles. In the winter of 1856-7 there was very little of this current. In crossing from Key West to Havana the Gulf Stream runs much stronger on the Cuban side. To some extent, navigators know this westerly current, and use it with great advantage when bound west. In one case in 1852 he knew of two vessels bound east past Tortugas which separated about 100 miles in twenty-four hours, by one captain knowing this current and the channel, while the other kept in the westerly current. The tide between the Quicksands and Tortugas sets flood N.N.E. and ebb S.S.E., differing from the charts.

Captain Wilson who has for several years been running on the vessel serving Fort Jefferson on Tortugas as a mail boat to and from Key West, says that for some three months prior to Feb. 11, 1857, there was a strong and decided westerly current on the north margin of the gulf, on the reef between Key West and Tortugas. It had then for some two months been constantly to the west. Running out from Tortugas on an E.S.E. or S.E. course, and tacking to the north or east of north when the point was reached, which in an ordinary gulf stream would bring him out somewhere from Sand Key light to six or seven miles west of it, which tack if there were no currents would bring him out abreast the Marquesas, he has six times in the last three months come out abreast the Quicksands, thus falling short of where he would have been had the water been still, by some eighteen to twenty miles, or some thirty miles west of Sand Key where he would have fetched during a full Gulf Stream current. It usu. ally takes about twenty hours to run both branches of this tack. There is no appearance of any current on or within the reef either way except the set of the tides. When the westerly cur. rent is running, he finds it better to beat up within the reef than to attempt to cross over into the Gulf Stream. Mr. W. thinks the current sometimes extends half way across to Cuba. He says, this westerly current has prevailed more or less, every winter for seven years that he has been running between Key West and the Tortugas; but never so strong as this winter (1857–8), or for so long a time, probably not over a month in any previous case. He thinks the westerly current mainly disappears during the prevalence of the regular summer trades.

I was informed by General Totten that Com. Bainbridge told him, that in a voyage made by him some fifty years since, when he supposed himself in the Gulf Stream, west of Cape Florida, he found by known landmarks that he had drifted a considerable distance to the westward instead of to the eastward.

I am indebted to Mr. Charles Tift, of Key West, for the fol. lowing notes :

"In December, 1856 (I think), the barque Joseph Hale from Philadelphia for New Orleans, got ashore ten miles southeast from Cape Florida light-house. She had passed round the *Isaacs,' and made the Orange Keys, steering for the Doubleheaded Shot Key's light. While looking out for the light, the ship apparently going seven knots, she struck, and proved to be in the position above stated.

"The ship Rockland from New Orleans to Boston was off the Pan of Matanzas at four o'clock (say March 25th, 1858), wind E.S.E., ship going per compass E.N.E., intending to sight Doubleheaded Shot Key light. At twelve o'clock saw what was supposed to be the light on Double-headed Shot Keys, and kept the

« AnteriorContinuar »