Page:Physical Geography of the Sea and its Meteorology.djvu/57

 Rh circulation in the ocean. The other "fork" runs between our shores and the Gulf Stream to the south, as already described. As far as it has been traced, it warrants the belief that it, too, runs up to seek the so-called higher level of the Mexican Gulf.

91. Effects of diurnal rotation upon the Gulf Stream.—The power necessary to overcome the resistance opposed to such a body of water as that of the Gulf Stream, running several thousand miles without any renewal of impulse from the forces of gravitation or any other known cause, is truly surprising. It so happens that we have an argument for determining, with considerable accuracy, the resistance which the waters of this stream meet with in their motion towards the east. Owing to the diurnal rotation, they are carried around with the earth on its axis towards the east, with an hourly velocity of one hundred and fifty-seven miles greater when they enter the Atlantic than when they arrive off the Banks of Newfoundland; for in consequence of the difference of latitude between the parallels of these two places, their rate of motion around the axis of the earth is reduced from nine hundred and fifteen to seven hundred and fifty-eight miles the hour. Hence this immense volume of water would, if we suppose it to pass from the Bahamas to the Grand Banks in an hour, meet with an opposing force in the shape of resistance sufficient, in the aggregate, to retard it two miles and a half the minute in its eastwardly rate. If the actual resistance be calculated according to received laws, it will be found equal to several atmospheres. And by analogy, how inadequate must the pressure of the gentle trade-winds be to such resistance, and to the effect assigned them!

92. The Gulf Stream cannot he accounted for by a higher level.—If therefore, in the proposed inquiry, we search for a propelling power nowhere but in the higher level of the Gulf, or in the "billiard-ball" rebound from its shores, we must admit, in the head of water there, the existence of a force capable of putting in motion, and of driving over a plain at the rate of four miles the hour, all the waters, as fast as they can be brought down by three