Storms sometimes originate in these currents, when concentrated, as in the West Indies, the China Sea, the Bay of Bengal, and Indian Ocean, while passing through the rainy belt, and move with the current to the north-west if issuing on the north side of it, and to the south-west if issuing on the south side of it, until they respectively get beyond the extreme limits of the trades, and then they curve to the eastward, imbedded in and following their current. The peculiar extension of the land to the east on the northern portions of South America, prevents the gathering of an aerial gulf similar to the one which we have described to the north-west, entering upon our division of the continent over the Gulf of Mexico. It is otherwise in the Indian Ocean, and there the storms are found issuing from the rainy belt on the southern side, sweeping over the Mauritius and other islands of that ocean, and often simultaneously with storms issuing on the north over the Bay of Bengal. Colonel Reid mentions instances and gives a diagram.[2]
These storms in milder forms issue from the rain belt at other points, and may issue any where, but will always be found most extensive and most violent, that is to say, as hurricanes and typhoons, in the concentrated volumes of counter-trade on the western side of the great oceans, within a few hundred miles of the lines of magnetic intensity and no variation, and when they form in the rainy belt they are highly electric. Most frequently, however, as we shall see, they form in these currents after they have issued from the rainy belt, and after they have passed the extreme limits of the trades and become subject to the circular and perpendicular magnetic currents which exist north and south of the longitudinal ones, and which when seen upon the magnetic needle, attract the filings and cause them to adhere—although but slight attraction or adhesion takes place where the longitudinal currents exist.
Such, then, are the atmospheric arrangements and phenomena of the trade-wind region, and the cause that produces them; such is the character and cause of the enlarged volume of counter-trade, which spreads out and blows over our country as permanently as the S. E. trades blow on the South Atlantic and South America, returning to us the rivers which had run from us to the sea.
CHAPTER VI.
Coming back now, to a consideration of the course and functions of the counter-trade after it leaves the northern limit of the surface-trades, we find it curves to the eastward and gradually assumes about an E. N. E. course, and becomes a W. S. W. current where it crosses the line of no variation, and continues on until it passes off over the Atlantic; and this course and curve is analogous to what may be found true of the counter-trades every where. It is best illustrated by the course of all the storms (in the American sense of the word, as distinguished from thunder showers and other brief rains), which have been traced north or south of the limits of the trades. It was found by Mr. Redfield in most of the storms investigated by him, which originated within, or north of the tropics.
Doubtless it was the actual course of the others, and that the investigation was imperfect. All the great autumnal, winter, or spring storms which have traversed the whole or any considerable portion of the territory of the United States, east of New Mexico, which have been investigated by Professors Espy, Loomis, Redfield, or others, have been found to follow this course. A storm which passed over Madeira, appears from the investigations of Colonel Reid to have followed the same law of curvature.
And so, doubtless, did another which he has described as passing over the Levant. The storms which supply the winter rains of California and Utah, reach them by this law of curvature and progress, after the northern limits of the trades have descended to the south with the sun, so that the counter-trades of the Pacific may descend to the surface and curve in upon them. But the absence of a concentration of the counter-trade, and its deficient action because of its passage over mountain ranges, and their location so near the northern limit of the trades that their storms can not expand and become extensive, as well as their weaker magnetic intensity, prevent their storms from becoming violent, and their supply of rain is not large and much of it falls in showers. The same is true of the Barbary States, of Syria, and Persia, and of Southern Europe; and indeed of all the countries of the globe which lie between the winter and summer extreme limits of the surface-trades, and without the limits of the two concentrated counter-trades. Enough appears in the writings of the meteorologists of Europe to show, that their long continued rains, which are analogous to our storms and are preceded by the formation of the true cirrus of the counter-trade, follow the same great law of curvature and progress; although the presence of the Gulf Stream with its mass of south polar waters on the western side of the British Islands, Denmark, and Norway supplies them with showers, and fogs, and cumuli from the west and north-west, and makes the mean of the surface winds of their storms somewhat variant from ours. A like law reversed prevails in the southern hemisphere. The storms of New Holland and the Indian Ocean, south of the limits of the trade, curve to the eastward and travel about south-east, their south-west being a clearing off wind as our north-west is, and precisely similar in all its other characteristics, where the relation of magnetic intensity is the same.
The storms of the Pacific on the S. W. coast of South America, in like manner travel to the S. E., flooding the western slopes of the mountain ranges with rain, and aggravated by the intensity of the magnetic currents at the extremity of the continent in a high latitude, meet the mariner in the face as he emerges from under the lee of the land and attempts to pass the Horn. It will ultimately be shown that the precipitation which takes place, as the storms and counter-trades pass north and east in the northern hemisphere and south and east in the southern hemisphere, is owing less to cold than increased magnetic intensity. And all this is the result of one great uniform law, existing every where, varying in its phenomena only in consequence of the difference in volume, and magneto-electric intensity of the portions of the counter-trade, as of the surface-trade at different places, and the different magnetic intensity of the local perpendicular and circular currents of the earth over which they pass, at different periods and at different points.