Page:Physical Geography of the Sea and its Meteorology.djvu/71

 Rh the seasons; the limit of its northern edge, as it passes the meridian of Cape Race (Plate VI.), being in winter about latitude 40-41°, and in September, when the sea is hottest, about latitude 45-46°. The trough of the Gulf Stream, therefore, may be supposed to waver about in the ocean not unlike a pennon in the breeze. Its head is confined between the shoals of the Bahamas and the Carolinas; but that part of it which stretches over towards the Grand Banks of Newfoundland is, as the temperature of the waters of the ocean changes, first pressed down towards the south, and then again up towards the north, according to the season of the year.

125. The phenomenon thermal in its character.—To appreciate the extent of the force by which it is so pressed, let us imagine the waters of the Gulf Stream to extend all the way to the bottom of the sea, so as completely to separate, by an impenetrable liquid wall, if you please, the waters of the ocean on the right from the waters in the ocean on the left of the stream. It is the height of summer: the waters of the sea on either hand are for the most part in a liquid state, and the Gulf Stream, let it be supposed, has assumed a normal condition between the two divisions, adjusting itself to the pressure on either side so as to balance them exactly and be in equilibrium, Now, again, it is the dead of winter, and the temperature of the waters over an area of millions of square miles in the North Atlantic has been changed many degrees, and this change of temperature has been followed likewise by a change in volume of those waters, amounting, no doubt, in the aggregate, to many hundred millions of tons, over the whole ocean; for sea-water, unlike fresh (§ 103), contracts to freezing, and below. Now is it probable that, in passing from their summer to their winter temperature, the sea-waters to the right of the Gulf Stream should change their specific gravity exactly as much in the aggregate as do the waters in the whole ocean to the left of it? If not, the difference must be compensated by some means. Sparks are not more prone to fly upward, nor water to seek its level, than Nature is sure with her efforts to restore equilibrium in both sea and air whenever, wherever, and by whatever it be disturbed. Therefore, though the waters of the Gulf Stream do not extend to the bottom, and though they be not impenetrable to the waters on either hand, yet, seeing that they have a waste of waters on the right and a waste of waters on the left, to which (§ 70) they offer a sort of