These general currents are greatly modified, and changed into various directions by the obstacles they encounter in their progress. The coast of America, and the numerous islands with which it is flanked, intercept the general current of the Atlantic, and create what navigators call the _Gulf Stream_. This great current enters the Gulf of Mexico, and, sweeping round the shores of that gulf, issues with accelerated velocity towards the north, by the channel between the southern point of Florida and the Bahama Islands.[32] It then rolls along the shore of North America, diminishing in velocity, but increasing in breadth, till it reaches the great bank of Newfoundland. There it suddenly turns towards the east and south-east, and flows with still decreasing velocity, towards the shores of Europe, the Azores, and the coasts of Africa. Navigators readily distinguish this current by the high temperature of its waters, their great saltness, their indigo color, and the shoals of sea-weed[33] that cover their surface. Humboldt, in May, 1804, observed its velocity in the twenty-seventh degree of latitude, and found it about eighty miles in twenty-four hours, though the north wind blew very strongly at the time of the observation. When it issues from the Gulf of Florida, its velocity resembles that of a torrent, and is sometimes five miles an hour, but at others not more than three. Between the nearest point of Florida, and the bank of Bahama, the breadth is only fifteen leagues, but a few degrees further north, it is seventeen; in the parallel of Charleston it is from forty to fifty leagues in breadth, and in latitude forty degrees and twenty-five minutes, this is increased to nearly eighty leagues. The waters of the torrid zone, being thus forcibly impelled towards the north-east, preserve their high temperature to such a degree, that, in latitude forty and forty-one degrees, it has been found to be seventy-two degrees of Fahrenheit, while out of the current the temperature of the water was only sixty-three degrees. In the parallel of New York the temperature of the Gulf Stream is equal to that of the sea in latitude eighteen degrees. When the current reaches the western islands of the Azores, where the breadth is about one hundred and sixty leagues, the waters still preserve a part of the impulsion they receive in the Gulf of Florida, nearly one thousand leagues distant. Hence the current proceeds to the Canaries and the coast of Africa, and in the latitude of Cape Blanco, where the waters flow towards the south-west, they mingle with the current of the tropics, and recommence their tour from east to west.