The Gulf Stream, as it issues from the Florida Channel, has a breadth of thirty-four miles, a depth of 2,200 feet, and moves at the rate of four and a half miles an hour. "Midway in the Atlantic, in the triangular space between the Azores, Canaries, and Cape de Verd Islands, is the great Sargassum Sea, covering an area equal to the Mississippi Valley; it is so thickly matted over with the Gulf weed (_Sargassum bacciferum_) that the speed of vessels passing through it is actually retarded, and to the companions of Columbus it seemed to mark the limits of navigation: they became alarmed. To the eye, at a little distance, it seemed sufficiently substantial to walk upon." The difference of temperature between the Gulf Stream and the waters it traverses constantly gives birth to tempests and cyclones. In 1780 a terrible storm ravaged the Antilles, in which 20,000 persons perished. The ocean quitted its bed, and inundated whole cities; the trunks of great trees and large parts of buildings were tossed wildly in the air. Numerous catastrophes of this kind have earned the Gulf Stream the title of the "King of the Tempests." So well had Maury studied the Gulf Stream and its storms, that he was enabled to point out the exact position of a vessel overtaken by a terrible gale. "In the month of December, 1859," says Figuier, "the American packet _San Francisco_ was employed as a transport to convey a regiment to California. It was overtaken by one of these sudden storms, which placed the ship and its freight in a most dangerous position--a single wave, which swept the deck, tore out the masts, stopped the engines, and washed overboard 129 persons, officers, and soldiers. From that moment the unfortunate steamer floated upon the waters, a waif abandoned to the fury of the wind. The day after the disaster the _San Francisco_ was seen in this desperate situation by a ship, which reached New York, although unable to assist her. Another ship met her some days after, but, like the other, could render no assistance. When the report reached New York two steamers were despatched to her assistance; but in what direction were they to go? what part of the ocean were they to explore? The authorities at the Washington Observatory were appealed to. Having consulted his charts as to the direction and limits of the Gulf Stream at that period of the year, Dr. Maury traced on a chart the spot to which the disabled steamer was likely to be driven by the current, and the course to be taken by the vessels sent to her assistance." The steamers went straight to the exact spot, and found the wreck; and although by that time the crew and passengers had been taken off by three passing vessels, it was certainly a triumph of science.