Page:Physical Geography of the Sea and its Meteorology.djvu/50

24 course, and in their effect they are as endless. Philosophy points to them as the chief cause of the Gulf Stream and of all the constant currents of the sea.

74. Early writers.—Early writers, however, maintained that the Mississippi River was the father of the Gulf Stream. Its floods, they said, produce it: for the velocity of this river in the sea (§ 70) might, it was held, be computed by the rate of the current of the river on the land.

75. Objection to the fresh-water theory.—Captain Livingston overturned this hypothesis by showing that the volume of water which the Mississippi River empties into the Gulf of Mexico is not equal to the three thousandth part of that which escapes from it through the Gulf Stream. Moreover, the water of the Gulf Stream is salt—that of the Mississippi, fresh; and the advocates of this fresh-water theory (§ 74) forgot that just as much salt as escapes from the Gulf of Mexico through this stream, must enter the Gulf through some other channel from the main ocean; for, if it did not, the Gulf of Mexico, in process of time, unless it had a salt bed at the bottom, or was fed with salt springs from below—neither of which is probable—would become a fresh-water basin.

76. Livingston's hypothesis.—The above quoted argument of Captain Livingston, however, was held to be conclusive; and upon the remains of the hypothesis which he had so completely overturned, he set up another, which, in turn, has also been upset. In it he ascribed the velocity of the Gulf Stream as depending "on the motion of the sun in the ecliptic, and the influence he has on the waters of the Atlantic."

77. Franklin's theory.—But the opinion that came to be most generally received and deep-rooted in the mind of seafaring people was the one repeated by Dr. Franklin, and which held that the Gulf Stream is the escaping of the waters that have been forced into the Caribbean Sea by the trade-winds, and that it is the pressure of those winds upon the water which drives up into that sea-head, as it were, for this stream.

78. Objections to it.—We know of instances in which the waters have been accumulated on one side of a lake, or in one end of a canal, at the expense of the other. The pressure of the trade-winds may assist to give the Gulf Stream its initial velocity, but are they of themselves sufficient to send such a stream of water all the way across the ocean, projecting by a single impress a volume