Page:Physical Geography of the Sea and its Meteorology.djvu/51

Rh of water from the shores of America to the shores of Europe, that exceeds in discharge the mighty Mississippi a thousand times? Reason teaches and examination shows that they are not. With the view of ascertaining the average number of days during the year that the N.E. trade-winds of the Atlantic operate upon the currents between 25° N. and the equator, log-books containing no less than 380,284 observations on the force and direction of the wind in that ocean were examined. The data thus attributed were carefully compared and discussed. The results show that within those latitudes, and on the average, the wind from the N.E. quadrant is in excess of the winds from the S.W. only 111 days out of the 365. During the rest of the year the S.W. counteract the effect of the N.E. winds upon the currents. Now, can the N.E. trades, by blowing for less than one-third of the time, cause the Gulf Stream to run all the time, and without varying its velocity either to their force or their prevalence?

79. Herschel's explanation.—Sir John Herschel maintains" that they can; that the trade-winds are the sole cause of the Gulf Stream; not, indeed, by causing "a head of water" in the West Indian seas, but by rolling particles of water before them somewhat as billiard balls are rolled over the table. He denies to evaporation, temperature, salts, and sea-shells, any effective influence whatever upon the circulation of the waters in the ocean. According to him the winds are the supreme current-producing power in the sea.

80. Objections to it.—This theory would require all the currents of the sea to set with the winds, or when deflected, to be deflected from the shore, as billiard balls are from the cushions of the table, making the littoral angles of incidence and reflection equal. Now, so far from this being the case, ""not" of the constant currents of the sea either makes such a rebound or sets with the winds. The Gulf Stream sets, as it comes out of the Gulf of Mexico, and for hundreds of miles after it enters the