This obliquity and consequent change of exposure are in degree precisely what the wants of the earth would seem to require. The direct action of the sun's rays upon the earth, particularly those portions which lie north and south of the tropics, is not the only source from which the supply of heat is derived. Although there is a general increase of heat in spring and summer when the sun travels north and of cold when he travels south in winter, yet there are frequent irreguJarities attending both. Very sudden and great changes occur in each of them. Frost sometimes, cool weather often, occurs in midsummer, and considerable heat and tornadoes in midwinter. And ordinarily the maxima and minima of each month and, indeed, of each week are widely apart. Even in the polar regions, in midwinter, where the sun does not shine at all, the same moderating changes with which we are conversant occur in degree.

Returning to a consideration of the arrangements for the diffusion of heat, we observe: First, that the earth itself is intensely heated in its interior. This is inferred, and justly, from the fact that the thermometer is found to raise about one degree for every fifty-five feet of descent-whether in boring artesian wells, exploring caves, or sinking shafts in the mines. It is demonstrated, also, by the existence of hot springs and the action of volcanoes. Heat is supposed to be conducted from the center toward the surface every where, but with difficulty and slowly. Probably it reaches the surface and exerts an influence, also, upon the weather through the ocean, and by heating it in its greatest depths. Doubtless a portion of the warmth of the ocean here is derived from that source, and it has its influence in changing the temperature of the deep-seated cold polar currents of the great oceans. Perhaps it may yet be found that the icebergs are detached by it in the polar seas-the observation of Dr. Kane point to such a result.

Heat is also carried, and in quantities which exert very considerable influence upon the weather, from the tropics to the poles by the great oceanic currents which flow unceasingly from one to the other.

The most important of these with which we are acquaintad is the Gulf Stream of the Atlantic. Gathering in the South Atlantic, passing north through the Caribbean Sea and the Gulf of Mexico, it issues out through the Bahama Channel and flows north along the eastern coast of the United States, but some distance from it, to Newfoundland, and from thence continuing to the north-east and spreading out over the surface of the North Atlantic Ocean, but this has comparatively little influence upon the weather of the United States. Western Europe, however, Greenland, the islands which lie in its course, are most materially influenced.

A like oceanic current exists in the Pacific Ocean, the influence of which may also be traced near the north-west coast of North America. A vast amount of heat is transported from the tropical to the temperate and frozen regions of the earth by these great oceanic currents.

Another supply of heat is derived from aerial currents which flow from the tropics toward the poles. These currents exist every where over the entire surface of the earth, but in more concentrated volumes along the great lines of "no

variation," and greater magnetic intensity, on the western side of the great oceans, over the eastern portions of the two continents of North America and Asia.

has

Still another supply of heat, during the sudden changes, at least, is produced by the action of terrestrial magnetism and electricity. Very great progress been made within a short period, in the investigation of the nature of these agents. The identity, or at least intimate association or connection of heat, light, electricity, and magnetism, always suspected, has been in various ways, and of a variety of experiments demonstrated. The influence of magnetism, if distinct from gravitation, is second only to that; and its agency in producing the phenomena we are considering is primary and controlling. We will only, in this connection, ask the reader to note the situation of the north magnetic poles, (for there are two of them,) which are, in fact, poles of cold, that is, it is colder there than even to the north of them. These poles are distinct from its geographical ones, and are situated not far from 71 deg. north latitude, and about 97 deg. west longtitude from Greenwich. We shall recur to this part of the subject again.

Such, briefly considered, are the principal arrangements by which heat is dif

fused over the earth.

the

Equally marked by infinite wisdom, and equally interesting and important are arrangements by which moisture is distributed. Doubtless the general belief is that this is a simple process; that water evaporates and rises till it meets a colder stratum of atmosphere, and then condenses and falls again; or that currents of air of different temperatures mingle and equalize their heat, and the aggregate mass when equalized in temperature is cooler, and therefore is unable to hold as much moisture in solution as the most heated portion had, and the excess falls in rain. But the process is by no means so simple, nor is heat the sole or most powerful agent concerned in it.

Currents of air do not mingle, but stratify. Evaporation from the surface of any given portion of the earth outside of the tropics does not alone supply that portion with rain.

In this respect, take your map of North America and note its pecularities. It extends from the Isthmus of Darien to the Artic regions, and from the 65th to the 160th meridian of west longtitude from Greenwich, and has upon its surface a type of every climate in the world. For the purpose of simplifying and demonstrating the matter in hand, let us divide it into five sections. Let the first section embrace Central America and Southern Mexico, south of 28 deg; the second, Northern Mexico and Southern New Mexico, California, etc, between the parallel of 28 degrees and 32 degrees; the third, Northern California, Utah, Southern Oregon and Western New Mexico, north of the parallel of 32 deg.; the fourth, the entire continent north of 42 deg.; and the fifth, the eastern United States, east of the meridian of 100 degrees. These divisions are not intended to be entirely accurate in their separation, but substantially so for the purpose of explaining the differences which exist in each. Now let us see in what a diverse manner, and to what a different extent, they are severally supplied with moisture. Central America and Southern Mexico lie within the tropics-their rains are

tropical rains. The season is divided into wet and dry, as are the seasons of all tropical countries which are not rainless. During the rainy season it rains a portion of nearly every day, and during the dry season the sky is clear, the air is pure, and rain seldom falls.

All around the earth within the tropics, over the land and over the sea, there is a belt of almost daily rains, varying in width, north and south, in different sections, but averaging about five hundred miles. This belt of daily rains is formed at and by the meeting of N. E. and S E. trades, and travels north and south with them, as they do with the sun, encircling the globe By this narrow belt a portion of the earth's surface, an average of some 35 degrees of latitude, is supplied with moisture. Wherever it is situated at any given period, the tropical rainy season exists; and when it is absent in its northern or southern transit, the dry season prevails. Southern Mexico is within the range of this moving belt, and in its course to the northward with the sun, in our summer from May to October, it arrives over, and covers that country with a rainy season. When the sun returns to the south, taking with it the trades and this belt of tropical rains, that portion of Mexico is without rain, and dry, and so continues until the rainy belt returns in the following year. While the belt is over Southern Mexico it is nearly all precipitation, and there is little evaporation; while that belt is absent it is all evaporation, with little or no rain. Surely this is not consistent with the prevailing belief of simple evaporation, ascent to a colder stratum, commingling, condensation and rain. Southern Mexico at least is not supplied by mere evaporation from its surface, and must therefore form an exception to that belief.

Turn now for a brief space to Northern Mexico, Southern New Mexico, and Southern California, between the parallels of 28 degrees and 32 degrees, and particularly west of the mountain ranges, we find an almost rainless region, sterile and worthless, resembling that which is found upon nearly the same parallels of north latitude in Northern Africa, Egypt, Arabia, and North-Western India; and in corresponding latitudes south of the Equator, in Peru, a portion of southern Africa, and the northern and middle portions of New Holland.

versa.

Turning now to Central and Upper California, Utah and Southern Oregon, we find still another peculiarity. Like Southern Mexico, they have a rainy and dry season, but at a different period, and for a different reason. The dry season of California, etc., is the summer of the northern hemisphere, and her rainy season the winter. California is therefore dry when Southern Mexico is wet, and vice The belt of rains which supplies California with moisture during her rainy seasons is the belt of extra-tropical rains, which extends from the northern limit of the north-east trades to the poles, encircling the earth. The southern edge of this extra-tropical belt is carried up on the western coast of America, and in that portion of the continent in summer, when the sun and trades, and the inter-tropical rainy belt travel to the north, and uncover California, etc., leaving them without rain for a period of about six months.

As the sun, with the trades, travels south, the southern edge of the belt of extra-tropical rain follows, and covers California, etc., again extending gradually

from the north to the south, and thus their wet season returns. The belts of rains which cover Mexico, Utah, New Mexico and California in summer and winter, are entirely distinct and different in character.

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. It is however obvious that evaporation alone, great or long continued, will not furnish the evaporating section with rain.

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 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 China and some other portion of Eastern Asia.

It is not only without a distinct rainy and dry, 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 on an average of only about twenty-five-if we except Norway, and one or two other places, where the fall of rain 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 and the average over the entire great interior valley is about forty inches falling 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 30 degrees, in some places, and 35 degrees in others, extending to the pole, with its southern edge traveling up 10 or more degrees in summer, leaving large portions of the earth subject to a dry season; and back again in winter to give them a rainy one? What produces the narrow belt of intertropical rains encircling the earth; traveling up and down every year over an average of 35 degrees 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 ad eastern portions of the United States, an average probably of onehalf or twenty inches runs off by the rivers to the ocean, or is carried away by the westerly or 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.”

But how is it that they thus return with such wonderful regularity, in a narrow traveling belt of daily rains within the tropics, and a movable belt of irregular rains without the tropics, extending to the poles, leaving a space on each side of the equator encircling the earth in like manner (except at two points, viz., Eastern Asia and Eastern North America), from which they do not go, and to which they do not return, and which is almost entirely unfurnished with rain? And all this without any relation, whatever, to the work of mere evaporation, or of the accidental or irregular commingling of winds with different dew points, or quantities of moisture in solution, or accidental, irregular changes of barometric pressure. It is one vast, wonderful, connected and regular system—co-extensive with the globe— necessary to the return of moisture from the oceans upon the most inconsiderable portion of it, and to the condensation of the moisture of evaporation; and by it the waters are returned from the oceans as regularly and bountifully upon the far interior of the great continents, in the same latitudes, as upon the "isles which rest in their bosoms."

CHAPTER II.

Our rivers return in the form of clouds, and in storms and showers, although, in truth, they return in 1egular, uniform, ordinarily invisible currents, and the storms and showers are but condensations in and discharges from portions of those currents, aided by the local moisture of evaporation.

These storms* extend over a considerable surface, rarely less than 100 miles in one direction or another, and sometimes 1500 or more. Distinct showers cover but a small surface, sometimes not more than 40 to 100 rods, as in the tornado, and rarely more than 10 miles. Belts of showers, each new one forming a little more to the south, often, in summer, pass across the country, following each other in succession; and these belts may be of considerable width, say 30 to 150 miles. The clouds which constitute the storms and showers differ in appearance and character, as well in the active as in the forming state. Clouds are of distinct characters, alike, substantially, everywhere under like circumstances; and a distinct nomenclature has been applied to them by Dr. Howard, of London. He notes three kinds of primary clouds, viz: Cirrus, Stratus, and Cumulus; and inasmuch as the boundary line between them is not very distinct, certain compounds of the three, viz: cirro-stratus, cirro-cumulus, and cumulo-stratus. This nomenclature is every where received, and portions of it are of great practical importance. The three principal descriptions of cloud, viz: the cirrus, the stratus, and the

* What we call storms denote regular rains.