So, too, we may know it from analogy. The laws of nature are uniform. There is a great end to be accomplished, _viz._: the distribution of forty inches of water, at regular intervals, over a large extent of country. The rivers are to return, and the clouds are to drop fatness, and seed time and harvest are not to cease. It is to be done and is done, by means of storms and showers, and pursuant to general laws, as immutable as the result. Most of these storms and showers, it has been found, and may be observed, move from the westward to the eastward. Then we may know, from analogy, that they do so in obedience to a general, uniform law; and so I might say with confidence, if our inquiry stopped here, it will ever be found by those who may hereafter examine them. But, 2d. There is a current in the atmosphere, all over the continent north of the N. E. trades, but in great volume over the United States, east of the meridian of 105 deg. W. from Greenwich--varying in different seasons, and upon different parallels, and flowing near the earth, when no surface wind interposes between them. In the vicinity of New York, the usual course of this current is from about W. S. W. to E. N. E. In the western and south-western portion of the United States, it is, doubtless, more southerly--varying somewhat according to the season--and in other sections varies in obedience to the general law of its origin, and progress. I have observed its course in many places, between the parallels of 38 deg. and 44 deg. N. _This current comes from the South Atlantic Ocean._ It is our portion of the aerial current, which flows every where from the tropics toward the poles, to which I have already alluded in connection with the distribution of heat. _It brings to us the twenty inches of rain which we lose by the rivers, and by the westerly winds, which carry off a portion of the local moisture of evaporation, and its action precipitates the remaining portion of that moisture. It spreads out over the face of our country, with considerable, but not entire uniformity. All our great storms originate in it, and all our showers originate in or are induced and controlled by it._ _From the varied action, inherent or induced, of this current, most of our meteorological phenomena, whether of wet or dry, or cold or warm weather, result_; and a thorough knowledge of its origin, cause, and the reciprocal action between it and the earth, is essential to a knowledge of the "_Philosophy of the Weather_." Let us then go down to the "chambers of the south," to the inter-tropical regions, of which we have said something in connection with a notice of Southern Mexico, and see where, and how this great aerial current originates. CHAPTER IV.