Page:Physical Geography of the Sea and its Meteorology.djvu/92

66 Stream exercises upon the storms of the North Atlantic, which take their rise within the tropics, is felt as far over even as the coast of Africa: it is also felt upon those which, though not intertropical in their origin, are known to visit the offings of the American coasts. These gales, in whatever part of the ocean east of the Gulf Stream they take their rise, march to the northwest until they join it, when they "recurvate," as the phrase is, and take up their line of march to the north-east along with it. Gales of wind have been traced from latitude 10°N. on the other side of the Atlantic to the Gulf Stream on this, and then with it back again to the other side, off the shores of Europe. By examining the log-books of ships, the tracks of storms have been traced out and followed for a week or ten days. Their path is marked by wreck and disaster. At a meeting of the American Association for the Advancement of Science, in 1854, Mr. Redfield mentioned one which he had traced out, and in which no less than seventy odd vessels had been wrecked, dismasted, or damaged.

175. More observations in and about the Gulf Stream a desideratum.—Now, what should attract these storms to the Gulf Stream, is a question which yet remains to be satisfactorily answered. A good series of simultaneous barometric observations within and on either side of the Gulf Stream is a great desideratum in the meteorology of the Atlantic. At the equator, where the trade-winds meet and ascend, where the air is loaded with moisture, and where the vapour from the warm waters below is condensed into the equatorial cloud-ring above, we have a low barometer.

176. Certain storms make for it and follow it.—How is it with the Gulf Stream when these storms from right and left burst in upon it, and, turning about, course along with it? Its waters are warm; they give off vapour rapidly; and, were this vapour visible to an observer in the moon, he no doubt would, on a winter's day especially, be able to trace out by the mist in the air the path of the Gulf Stream through the sea.

177. How aqueous vapour assists in producing winds.—Let us consider the effect of vapour upon winds, and then the importance of the observations proposed (§ 175) will perhaps be better appreciated. Aqueous vapour assists in at least five, perhaps six, ways to put air in motion and produce winds. (1.) By evaporation the air is cooled; by cooling its specific gravity is changed, and, consequently, here is one cause of movement in