The Philosophy of the Weather. And a Guide to Its Changes

by T. B. Butler

Fig. 4.

IN WINTER.

Here again in this section of the continent, as in Mexico, evaporation is going on for six months of the year, and were it not for the return of the belt of rains from the north, in the fall, would go on for the entire year without precipitation; and for the other six months precipitation is vastly in excess. Nor can this be reconciled with, or explained by, the Huttonian or any other received theory of rain. Here again it is obvious that evaporation alone, however great or long continued, will not furnish the evaporating section with rain.

The northern portion of the continent lies beneath the zone of extra-tropical rains, and north of the northern limit of the N. E. trades—is never uncovered from it, and has no distinct rainy or dry season, although more rain falls at certain periods, and in certain localities, than at others. The climate of that part of Oregon which lies upon the Pacific, and the character of its rains, resemble those of North-western Europe, and will be further explained hereafter.

Coming to the portion of the continent which we occupy, the 5th section, we find it different still—a most favored region. Portions of it—Eastern Texas, for instance—are upon the same parallels of latitude as the rainless regions of Northern Mexico, etc. Eastern Texas, however, is not rainless. Other portions are upon the same parallels as California, etc., yet have no distinct rainy and dry season. We repeat, this section is a most favored region—without a parallel upon any portion of the earth’s surface, except, in degree, in China and some other portions of Eastern Asia.

It is not only without a distinct rainy and dry season, but it is watered by an average, annually, of more than forty inches of rain, while Europe, although bounded on three sides by seas and oceans, and apparently much more favorably situated, receives annually an average of only about twenty-five—if we except Norway, and one or two other places, where the fall is excessive. The distribution of this supply of moisture over the United States is, in other respects, wonderful. Iowa, in the interior of the continent, far away from the great oceans, on the east or west, or the Gulf of Mexico on the south, receives fifty inches; some ten or fifteen inches more than fall upon the slope east of the Alleghanies, and contiguous to the great Atlantic (from which all our storms are, erroneously, supposed to be derived), and the average over the entire great interior valley is about forty-five inches, falling at all seasons of the year.

Observe, then, by way of recapitulation: Southern Mexico has a rainy season furnished by the belt of inter-tropical rains, which travels up over it from the south in summer. California has a rainy season, which is furnished by the extra-tropical belt of rains, which travels down from the north, and covers it in winter. Northern Mexico and the adjoining regions west of the 100th meridian are between the limits of the two, and neither travels far enough to reach them, except for brief and uncertain periods; they are comparatively rainless; while the eastern portion of the continent, in all latitudes, unlike the others, is without a distinctly marked dry season, or a rainless region, and with the exception of occasional droughts, is abundantly supplied with rain at all seasons of the year.

And now, what is the explanation of all this? What produces the extra-tropical belt of regular rains surrounding the earth, north of the parallel of 30° north, in some places, and 35° in others, extending to the pole, with its southern edge traveling up ten or more degrees in summer, leaving large portions of the earth subject to a dry season; and back again in the winter to give them a rainy one? What produces the narrow belt of inter-tropical rains, encircling the earth; traveling up and down every year over an average of 35° of latitude, supplying every portion of it alternately with rain? And what connects the two together over the eastern portion of North America, so as to leave no distinctly marked wet and dry season, and no rainless and sterile portion there? Are all these the result of simple evaporation, ascent to a colder region, condensation, and descent again? Demonstrably not. Of the forty inches which fall annually upon the middle and eastern portions of the United States, an average probably of one-half or twenty inches, runs off by the rivers to the ocean, or is carried away eastward by the westerly and north-westerly evaporating winds. The same is true, in degree, of the rain which falls upon the other portions. Evaporation, therefore, could not keep up the supply. From whence, then, does it come? this twenty inches, thus lost by the rivers and winds, and with such wonderful regularity every year.

“All the rivers run into the sea, yet the sea is not full. Note the place whence the rivers come, hither they return again.”