THE PHILOSOPHY

OF

THE WEATHER.

AND

A GUIDE TO ITS CHANGES.

BY T. B. BUTLER.

NEW YORK:
D. APPLETON & COMPANY,
NOS. 346 & 348 BROADWAY.
1856.

Entered according to Act of Congress, in the year 1856, by
T. B. BUTLER,
In the Clerks Office of the District Court of the District of Connecticut.

ELECTROTYPED BY
THOMAS B. SMITH,
82 & 84 Beekman Street.

PRINTED BY
J. F. TROW,
379 Broadway.

INTRODUCTION.

The atmospheric conditions and phenomena which constitute “The Weather” are of surpassing interest. Now, we rejoice in the genial air and warm rains of spring, which clothe the earth with verdure; in the alternating heat and showers of summer, which insure the bountiful harvest; in the milder, ripening sunshine of autumn; or the mantle of snow and the invigorating air of a moderate winter’s-day. Now, again, we suffer from drenching rains and, devastating floods, or excessive and debilitating heat and parching drought, or sudden and unseasonable frost, or extreme cold. And now, death and destruction come upon us or our property, at any season, in the gale, the hurricane, or the tornado; or a succession of sudden or peculiar changes blight our expected crops, and plant in our systems the seeds of epidemic disease and death. These, and other normal conditions, and varied changes, and violent extremes, potent for good or evil, are continually alternating above and around us. They affect our health and personal comfort, and, through those with whom we are connected, our social and domestic enjoyments. They influence our business prosperity directly, or indirectly, through our near or remote dependence upon others. They limit our pleasures and amusements—they control the realities of to-day, and the anticipations of to-morrow. None can prudently disregard them; few can withhold from them a constant attention. Scientific men, and others, devote to them daily hours of careful observation and registration. Devout Christians regard them as the special agencies of an over-ruling Providence. The prudent, fear their sudden, or silent and mysterious changes; the timid, their awful manifestations of power; and they are, to each and all of us, ever present objects of unfailing interest.

This interest finds constant expression in our intercourse with each other. A recent English writer has said: “The germ of meteorology is, as it were, innate in the mind of every Englishman—the weather is his first thought after every salutation.” In the qualified sense in which this was probably intended, it is, doubtless, equally true of us. Indeed, it is often not only a “first thought” after a salutation, but a part of the salutation itself—an offspring of the same friendly feeling, or a part of the same habit, which dictates the salutation—an expression of sympathy in a subject of common and absorbing interest—a sorrowing or rejoicing with those who sorrow or rejoice in the frowns and smiles of an ever-changing, ever-influential atmosphere.

If consistent with our purpose, it would be exceedingly interesting to trace the varied forms of expression in use among different classes and callings, and see how indicative they are of character and employment.

The sailor deals mainly with the winds of the hour, and to him all the other phases of the weather are comparatively indifferent. He speaks of airs, and breezes, and squalls, and gales, and hurricanes; or of such appearances of the sky as prognosticate them. The citizens, whose lives are a succession of days, deal in such adjectives as characterize the weather of the day, according to their class, or temperament, or business; and it is pleasant, or fine, or very pleasant or fine; beautiful, delightful, splendid, or glorious; or unpleasant, rainy, stormy, dismal, dreadful or horrible. The farmer deals with the weather of considerable periods; with forward or backward seasons, with “cold snaps” or “hot spells,” and “wet spells” or “dry spells.” And there are many intermediate varieties. The acute observer will find much in them to instruct and amuse him, and will probably be surprised to find how much they have to do with his “first impressions” of others.

But I have a more important object in view. I propose to deal with “The Philosophy of the Weather”—to examine the nature and operation of the arrangements from which the phenomena result; to strip the subject, if possible, of some of the complication and mystery in which traditionary axioms and false theories continue to envelop it; to endeavor to grasp its principles, and unfold them in a plain, concise, and systematic manner, to the comprehension of “the many,” who are equal partners with the scientific in its practical, if not in its philosophic interest; and to deduce a few general rules by which its changes may be understood, and, ultimately, to a considerable extent, foreseen.

This is not an easy, perhaps not a prudent undertaking. Nor is my position exactly that of a volunteer. A few words seem necessary, therefore, by way of apology and explanation.

In the fall of 1853, in the evening of a fair autumnal day, I started for Hartford, in the express train. Just above Meriden, an acquaintance sitting beside me, who had been felicitating himself on the prospect of fine weather for a journey to the north, called my attention to several small patches of scud—clouds he called them—to the eastward of us, between us and the full clear moon, which seemed to be enlarging and traveling south—and asked what they meant.

“Ah!” said I, “they are scud, forming over the central and northern portions of Connecticut, induced and attracted by the influence of a storm which is passing from the westward to the eastward, over the northern parts of New England, and are traveling toward it in a southerly surface wind, which we have run into. They seem to go south, because we are running north faster than they. You see them at the eastward because they are forming successively as the storm and its influence passes in that direction, and are most readily seen in the range of the moon; but when we reach Hartford you will see them in every direction, more numerous and dense, running north to underlie that storm.”

I had seen such appearances too many times to be deceived. It was so. When we arrived at Hartford they were visible in all directions, running to the northward at the rate of twenty-five miles an hour. In the space of forty minutes we had passed from a clear, calm atmosphere (and which still remained so), into a cloudy, damp air, and brisk wind blowing in the same direction we were traveling, and toward a heavy storm. My friend passed on, and met the southern edge of the rain at Deerfield, and had a most unpleasant journey during the forenoon of the next day. Taking the cars soon afterwards, in the afternoon, for the south, I found him on his return.

“Shall I have fair weather now till I get home?” said he.

“There are no indications of a storm here, or at present,” I replied, “but we may observe them elsewhere, and at nightfall.”

He kept a sharp look-out, and, as we neared New Haven, discovered faint lines of cirrus cloud low down in the west, extending in parallel bars, contracting into threads, up from the western horizon, in an E. N. E. direction toward the zenith.

“Now, what is that?” said he.

“The eastern outlying edge of a N. E. storm, approaching from the W. S. W. It is now raining from 150 to 200 miles to the westward of the eastern extremity of those bars of cirrus-condensation; perhaps more, perhaps less; and under those bars of condensation the wind is attracted, and is blowing from the N. E. toward the body of the storm, and where the condensation is sufficiently dense to drop rain. That dense portion will reach here, and it will rain from twelve to fifteen hours hence. As we pass along the shore, and run under that out-lying advance cirrus-condensation, we shall see that the vessels in the Sound have the wind from the N. E., freshening, but we shall continue to have this light and scarcely-perceptible air from the northward for a time—the N. E. wind always setting in toward an approaching storm, out on the Sound, much sooner than upon the land.”

As we approached the storm, and the storm us, the evidence of denser condensation at the west, and of wind from the east, blowing toward it, became more apparent. The fore and aft vessels were running “up Sound” with “sheet out and boom off,” before a fresh N. E. breeze, and my friend was astonished.

“I must understand this,” said he; “how is it?”

“All very simple. The page of nature spread out above us is intelligible to him who will attentively study it. The laws which produce the impressions and changes upon that page, are few and comprehensible. Although there is great variety, even upon the limited portion which is bounded by our horizon, there is also substantial uniformity; and, although the changes are always extensive, often covering an area of one thousand miles or more, and our vision can not extend in any direction more than from thirty to fifty, yet those changes are always, to a considerable extent, intelligible, and may often be foreseen.”

“Has meteorology made such progress?”

“By no means. It has, indeed, been raised to the dignity of a science, and professorships endowed for its advancement. Some books have been written, and many theories broached in relation to it; and innumerable observations of the states of the barometer and thermometer, of the clouds, and the quantity of fallen rain, and the direction and force of the wind—made and recorded simultaneously in different countries—have been published and compared; and a great many important facts established, and tables of ‘means’ constructed, and just inferences drawn, yet the few and simple arrangements upon which all the phenomena depend, and their philosophy, have not yet been clearly elicited or understood.”

“Have not the ‘American Association for the Advancement of Science’ arrived at some definite and sound conclusion upon the subject?”

“No; it has been with them, for many years, an interesting subject for papers and debate. Some very valuable articles, upon particular topics, or branches of the subject, have been read and published. But the Cyclonologists, as they term themselves, and who seem to think the great question is, ‘Are storms whirlwinds?’ appear with new editions and phases of their favorite views as regularly as the annual meeting recurs; and, though they have not convinced, they seem to have silenced their opponents. The only conclusion, however, judging from their debates, to which the Association appear to have come with any considerable unanimity, is, that they are yet without sufficient authentic observations and well-established facts, to authorize the adoption of the Huttonian, Daltonian, Gyratory, or Aspiratory, or any of the other numerous theories which abound. And they are right. The subject is mystified by these theories and speculations of the study, founded on barometrical and thermometrical records, and the direction and force of the surface winds.

“The qualities of heat were among the earlier discoveries of science, and all the phenomena of the weather were forthwith attributed to its influence. Hastily-formed and erroneous views of its power, and the manner of its action in particular localities, and under particular circumstances, have retained the credence accorded to them when first announced, although subsequent discoveries have shown their fallacy; some new theory of modification having been invented to reconcile the discrepancies as soon as they appeared. Perhaps it is not too much to say (however it may seem to one not thoroughly acquainted with the subject, who does not know that the primary and secondary modifying hypotheses found in Kämtz, may be counted by hundreds) that there is not remaining in any other science, and possibly in all others, an equal amount of false and absurd theory, and of forced and unnatural grouping of admitted facts to sustain it, as in meteorology as at present taught and received. Astronomy, as a science, is almost perfected—the nature, and size, and orbits, of the distant worlds around us are known—while constant changes and alternating atmospheric conditions, which all occur within less than six miles of us, affecting all our important interests, and obvious to our senses, although much talked off, and made the objects of many theories, are but little understood.”

“How, then, did you acquire the information you seem to possess?”

“By studying ‘the countenance of the sky,’ for in no other way has such information ever been, or can it ever be, acquired. By a long-continued, daily, and sometimes hourly observation of the clouds and currents of the atmosphere, in connection with such reports of the then state of the weather elsewhere, as have fallen under my notice, and the effect of its changes upon the animal creation—for very much can be learned from them. Yonder flock of black ducks that sit on that inshore rock, above the tide—the wildest and most suspicious of all their tribe—although the air is calm about them, know well that a storm is at hand. They probably both see and feel it. As twilight approaches they will fly away inland, forty or fifty miles perhaps, and settle among the lilies or grass which surround some fresh-water pond, certain of remaining while the storm lasts, and for one day at least, out of danger, and undisturbed. Many a time, in my boyhood, have I heard, in the stillness of evening, the whistling of their wings, as they swept up the Connecticut valley, to seek, on the borders of the coves, and in the creeks of the meadows, a concealed and safe feeding-place during a coming storm. And many a time in the autumn, after they had all passed down for the season, when the indications of an approaching storm were clearly visible at nightfall, have I waited for them to return, on the eastern margin of a bend in the cove, on the eastern side of a creek, to shoot them, though invisible, by shooting across the head of the wake, which they made upon the water in alighting, and from which the few remaining rays of twilight that came from the western sky were reflected.

“But I am far from being singular in this. That page is more extensively read than is generally supposed. Many plain, unassuming men—farmers, shipmasters, and others within the circle of my acquaintance—know more, practically, of the weather than the most learned closet-theorist, or the most indefatigable recorder of its changes. Every one, by studying the page of nature above him, as he would the page of any other science, and testing, by observation, the numerous theories invented to account for the varied phenomena, may learn much, very much, that will be useful and interesting to him, and which he can never learn from books, or instruments, or theories alone.”

“Well,” said my friend, “I am too far advanced in life, as are many others, to commence such observations, and you must publish.”

I demurred, and he insisted.

“It is difficult to spare the time; and I can not neglect my profession,” I urged.

“Where there is a will there is a way,” he replied.

“It is difficult to make one’s self understood without many illustrations.”

“Very well, they are easily obtained.”

“But they cost money, and it is said ‘science will not pay its way’ like fiction and humbug.”

“That,” said he, “is a libel—such science will. Every one is interested in the weather—all talk about it—and thousands would carefully observe it, if they could be correctly guided in their observations.”

“I may get into unpleasant controversy.”

“Suppose you do; you can yield your position if wrong, and maintain it if right, and magna est veritas.”

“But I may be mistaken in some of the views to which it will be necessary to advert, if I attempt to systematize the subject.”

“Be it so—your mistakes may lead others to the discovery of the truth. Besides, the weather is common property, and every one has a right to theorize about it, or to talk about it, as they please—even to call a stormy day a pleasant one, or make any other mistaken remark concerning it; and every other person is entitled to a like latitude of reply. And further,” said he, with some emphasis, “no important observation, in relation to a subject of such interest, should be lost; and, if you have observed one new fact, or drawn one new and just inference from those which have been observed by others; and especially if, from observation and reading, you can deduce from the phenomena an intelligible, observable, general system, it is not only your right, but duty, to make it known. Such a knowledge of the true system is greatly desired by every considerate man.”

To my friend’s last argument I was compelled to yield. I could make no reply consistent with the great principles of fraternity, which I shall ever recognize. The promise was given. My friend went on his way, and I went to the daguerreotypist to procure a copy of the then appearance of the sky, as the first step toward its fulfillment. The fulfillment of that promise, reader, you will find in the following work. It was commenced as an article for a magazine, but it has grown on my hands to a volume. Justice could not well be done to the subject in less space. It has been written during occasional and distant intervals of relaxation from professional avocations, or during convalescence from sickness, and it is, for these reasons, somewhat imperfect in style and arrangement. But I have no time to rewrite. There is much in it which will be old to those who read journals of science, but new to those who do not. There is more which will be new to all classes of readers, and may, perhaps, be deemed heretical and revolutionary by conservative meteorologists; yet I feel assured that the work is a step in the right direction—that it contains a substantially accurate exposition of the Philosophy of the Weather, and valuable suggestions for the practical observer.

I have inserted my name in the title-page, contrary to my original intention, and at the suggestion of others; for I have no scientific reputation which will aid the publisher to sell a copy. Nor do I desire to acquire such reputation. It can never form any part of my “capital in life.” Nor has it influenced me at all in preparing the work. I have aimed to fulfill a promise, too hastily given, perhaps—to put on record the observations I have made, and the inferences I have drawn from those of others—to induce and assist further observations, and, if possible, of a general and connected character—and to impress those who may read what I have written with the belief, that they will derive a degree of pleasure from a daily familiarity with, and intelligent understanding of, the “countenance of the sky,” not exceeded by that which any other science can afford them.

I have examined, with entire freedom and fearlessness (but I trust in a manner which will not be deemed censurable or in bad taste) the theories and supposed erroneous views of others, for, in my judgment, the advancement of the science requires it. Says Sir George Harvey, in his able article on Meteorology, written for the Encyclopædia Metropolitana:

“It is humiliating to those who have been most occupied in cultivating the science of meteorology, to see an agriculturist or a waterman, who has neither instruments nor theory, foretell the future changes of the weather many days before they happen, with a precision which the philosopher, aided by all the resources of science, would be unable to attain.”

The admissions contained in this paragraph, in relation to the comparative uselessness of instruments and theories, and the value of practical observation, are both in a good measure true. And the time has come, or should speedily come, when “pride of opinion,” and “esprit du corps,” among theorists and philosophers, should neither be indulged in, nor respected; and when their theories should be freely discussed, and rigidly tested by the observations of practical men. Such measure, therefore, as I have meted, I invite in return. Let whatever I have advanced, that is new, or adopted that is old, be as rigidly tested, and as freely discussed. Let the errors, if there be any—and doubtless there are—be detected and exposed. Let the TRUTH be sought by all; and meteorology, as a PRACTICAL SCIENCE, advance to that full measure of perfection and usefulness, of which it is unquestionably susceptible.

TABLE OF CONTENTS.

THE PHILOSOPHY OF THE WEATHER.

CHAPTER I.

Heat and moisture are indispensable to the fertility of the earth. Without suitable arrangements for their diffusion and distribution, and within the limits of certain minima and maxima, it would not have been habitable, or the design of its Creator perfected. These arrangements therefore exist, and “while the earth remaineth seed time and harvest shall not cease.” Few and simple in their character, though necessarily somewhat complicated and irregular in their operation, the ultimate result is always attained. A beautiful system of compensations supplies the losses of every apparent irregularity in one section or crop, by the abundance of others.

From the operation of these few, simple, connected, and intelligible arrangements for the diffusion of heat and the distribution of moisture over the earth, result all the phenomena which constitute the weather; and by studying them, and their operation, we may acquire an accurate knowledge of its “Philosophy.”

The necessary heat is furnished, or produced, mainly by the direct action of the sun’s rays; and the most obvious feature in the arrangements for its diffusion is that by which the sun is made to shine successively and alternately upon different portions of the earth. Nothing animate or organic could endure his burning rays, if they shone continuously or vertically upon one point, or could exist without their occasional presence. Hence the provision for a diurnal rotation, to prevent the exposure of any portion of the globe to the action of those rays for twenty-four consecutive hours, except for a limited period, and at a considerable angle, in the polar regions. But the earth is spheroidal, and a diurnal revolution would still leave that portion which lies under the equator too much, and the other too little, exposed to the action of the sun. This is obviated by an annual revolution of the earth around the sun, and an obliquity of its axis, by reason of which the northern and southern portions are alternately and, as far as the tropics vertically, exposed to the sun; and it is made to travel (so to speak) from tropic to tropic, producing summer and winter, and other important phenomena.

This obliquity and consequent change of exposure are in degree precisely what the wants of the earth would seem to require. If it was greater, the sun would travel further north and south, but the alternate winters would be longer and more severe. If it was less, the end would not be as perfectly attained.

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 irregularities 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. An extract or two from the register found in Dr. Kane’s narrative of the “Grinnell Expedition” will illustrate this.

January 1851, (Latitude about 74°, Longitude about 70°).

These extracts are instructive. It will be seen that on the 3d of January, when the sun had been absent some weeks, it was calm, the thermometer stood at 26° below zero (the - or minus mark before the figures indicates that), and the barometer at 29.62, with blue sky, somewhat misty or hazy—(the letter “m.” standing for misty or hazy)—a state of the air which existed most of the time when it did not snow or rain, and therefore is of no importance in this connection. The next day the thermometer began to rise, and the barometer to fall. On the 5th it clouded over, and the thermometer rose rapidly, and on the 6th it had risen more than 25°, and snow fell. On the 7th it cleared off, the thermometer fell rapidly, and the barometer rose. On the 8th the thermometer had fallen to 21° below zero, and the barometer had risen to 30.14. Another instance, in all respects similar, occurred the latter part of the month. We shall see hereafter that these changes are precisely like those which occur with us, and every where. That, as in the polar regions, and whether the sun be present or absent, or obscured by clouds, and by night as well as by day, the changes from warm to cold and from cold to warm are sudden and great, and that the latter are connected with the fall of rain and snow—that every where in winter it moderates to storm.

Many other instructive instances, especially in relation to the great difference in the seasons in our own country, and upon the same parallels elsewhere, might be cited if it were necessary. But they will more appropriately appear in the sequel.

Fig. 1.

In the above cut the isothermal lines are Centigrade. The zero of the Centigrade thermometer is the freezing point of water, or 32° of Fahrenheit. The boiling point of water is 100° Centigrade, or 212° Fahrenheit. A degree of Centigrade is equal to one degree and four-fifths, Fahrenheit. The 0° line of the cut, therefore, is 32° of Fahrenheit—the line of 5° above is 41° Fahrenheit—the line of 5° below is 23° Fahrenheit, and so on. The reader, who is not familiar with the difference in the scale of the thermometer, is desired to remember this; for we shall make occasional extracts in which the temperature is given in the Centigrade scale.

The cause of those irregularities, especially in the same seasons of different years, and when very great, is often sought and supposed to be found in the presence or absence of spots on the sun, ice floes and bergs in the Atlantic, etc., etc. But neither the spots, nor ice, nor other local causes produce them. The cause will be found in the character of the arrangements we are considering, and the irregular action of the power which controls them.

Nor is the temperature of the northern hemisphere, north of the tropics, equal in the same latitudes. Very great diversities exist in the “annual mean” as well as the “mean” of the different seasons. Accurate observations at many points have enabled men of science to demonstrate this by drawing isothermal lines (i. e., lines of equal average annual heat) from point to point around the earth, which show at a glance these differences. The annexed cut is a polar projection of the isothermal lines of the northern hemisphere, as far down as the tropic, copied from Kaemtz’s Meteorology. The dotted lines show the parallels of latitude, the dark lines the isothermal lines, or lines of equal annual average temperature. The reader is desired to observe how rarely they correspond with the parallels of latitude, and how they fall below in a few instances, and in others with great uniformity rise almost to the pole.

Take, for example, the isothermal line of 0 or zero—that is, the line where the mean or average height of the thermometer for the year is at zero. At Behring’s Straits this line is a little below the Arctic circle, or the parallel of 66.30 north latitude. Passing east over North America, it descends into Canada, almost to Lake Superior, and to about the 50th parallel: that is to say, it is on an average during the year as cold on our continent at the 50th parallel as it is near Behring’s Straits at the 65th parallel. Passing east, the line of zero rises again over the Atlantic Ocean until, in the meridian of Spitzbergen, it reaches, within the Arctic circle, up almost to the 75th parallel. So, too, the isothermal of 5° below zero, which is below the 60th parallel in Siberia, rises in the North Sea, above Behring’s Straits, to the parallel of 75°, descending on the continent in North America to the 55th parallel, and rising again almost to the pole at Spitzbergen, to descend again in Siberia, while the isothermals of 10° and 15° below zero, which in North America are but just above the latitude of 60° and 75° respectively, ascend abruptly surrounding the magnetic pole, and falling short of the geographical one. Let this projection of the lines of equal temperature, and particularly the situation of the magnetic poles, be studied well, for we shall recur to it hereafter in illustration of many important portions of our subject.

It is apparent from these facts, and were it necessary might be rendered still more so by referring to others, that other causes operate in the distribution of heat over the earth besides the direct action of the sun’s rays upon it. Doubtless very considerable allowance is to be made for the difference of seasons, and difference during the same season upon the land and upon the ocean; in mountainous countries and level ones. But making every allowance for them, the fact that other causes have a controlling influence in producing the deviations still remains most obvious. Neither the difference of temperature between the land and the ocean, or land surfaces of unequal elevations, will account for the elevation of the isothermal lines on different portions of the ocean, or their extension around the magnetic poles.

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 rise about one degree for every fifty-five feet of descent—whether in boring artesian wells, exploring caves, or sinking shafts in 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. It is also supposed to be conducted from the tropical regions toward the poles. Such is the opinion of Humboldt. (Cosmos, vol. i. p. 167.)

Probably it reaches the surface and exerts an influence, also, upon the weather through the ocean, and by heating it in its greatest depths. Little attention has been paid, so far as I am informed, to the question how far the ocean is thus heated in tropical latitudes. Doubtless a portion of the warmth of the ocean there 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 observations of Dr. Kane point to such a result. (Grinnell Expedition, p. 113, and also chap. 48.)

Little need be said of the inconsiderable quantities of heat supposed to be derived by radiation from the stars, the planets, and from space. If any such are derived they are too inconsiderable to be of importance in this inquiry.

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 acquainted is the Gulf Stream of the Atlantic. Gathering in the South Atlantic, and 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 ocean—a portion of it mingling with the waters of the North Atlantic in passing—it flows up on the western coast of Europe, around the Faroe Islands, and Spitzbergen, to the polar sea; passing around Greenland, and perhaps through its Fiords, it descends again through the sounds and channels of the Arctic regions into Baffin’s Bay, and through Davis’s Straits, burdened with the icebergs and floes of the polar waters, to return again to the South Atlantic. For reasons which will appear in the sequel, it has comparatively little influence upon the weather of the United States. Western Europe, however, Greenland, the islands which lie in its course, and the polar seas, are most materially influenced. Although not the only cause, it has very much to do with the remarkable elevation of the isothermal lines over the Northern Atlantic, and upon Western Europe, as seen upon the map.

A like oceanic current exists in the Pacific Ocean, the influence of which may also be traced upon the map by the elevation of the isothermal lines at the northern extremity of that ocean, and upon 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 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. Not, as meteorological writers suppose, in the upper portions of the atmosphere, having risen in the trade-wind region and run off at the top toward the poles by force of gravity, but near, and sometimes in contact with the earth. The influence of these aerial currents upon the temperature of the atmosphere, and in producing the phenomena we are to consider, is exceedingly important. We shall have occasion to examine them with great care and minuteness under another head, for upon them, more than any other portion of the arrangements, depend not only the diffusion of heat, but also the distribution of moisture.

Still another supply of heat, during the sudden changes, at least, is produced by the action of terrestrial magnetism and electricity. Very great progress has 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 by 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); the manner in which the isothermal lines surround them; the fact that they are poles of cold, i. e., that it is colder there than even to the north of them. We shall recur to this part of the subject again.

Such, briefly considered, are the principal arrangements by which heat is diffused over the earth.

Equally marked by infinite wisdom, and equally interesting and important, are the 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, according to the Huttonian theory, 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. Vast and wonderful, coextensive with the globe itself, and perfectly connected, is the machinery by which that supply is furnished even to the most inconsiderable portion of its surface.

Take your map of North America and note, in this respect, its peculiarities. It extends from the Isthmus of Darien to the Arctic regions, and from the 65th to the 160th meridian of west longitude from Greenwich, and has upon its surface a type of every climate in the world. For the purpose of simplifying and illustrating the matter in hand, let us divide it into five sections. Let the first section embrace Central America and Southern Mexico, south of 28°; the second, Northern Mexico and Southern New Mexico, California, etc., between the parallels of 28° and 32°; the third, Northern California, Utah, Southern Oregon, and Western New Mexico, north of the parallel of 32°; the fourth, the entire continent north of 42°; and the fifth, the eastern United States, east of the meridian of 100°. These divisions are not intended to be entirely accurate in their separation, but substantially so for the purpose of illustrating the differences which exist in each.

The accompanying diagram shows approximately, by dotted lines, the divisions.

Fig. 2.

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° 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, and 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, and to the Huttonian theory.

But we shall recur again to the peculiarity of distribution within the tropics.

Turn now for a brief space to Northern Mexico, Southern New Mexico, and Southern California. In Northern Mexico, Southern New Mexico, Utah, and California, between the parallels of 28° and 32°, 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, Beloochistan, Afghanistan, 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. Why Northern Mexico and the other countries named are thus sterile and comparatively rainless, we shall see hereafter, when we examine critically the machinery of distribution as it operates within the tropics. It is the fact that it is thus sterile and rainless to which we desire to call attention in this place.

Mr. Bartlett thus describes it:

“On leaving the head waters of the Concho, nature assumes a new aspect. Here shrubs and trees disappear, except the thorny chaparral of the deserts; the water-courses all cease, nor does any stream intervene until the Rio Grande is reached, three hundred and fifty miles distant, except the muddy Pecos, which, rising in the Rocky Mountains, near Santa Fé, crosses the great desert plain west of the Llano Estacado, or Staked Plain.

“From the Rio Grande to the waters of the Pacific, pursuing a westerly course along the 32d parallel, near El Paso Del Norte, there is no stream of a higher grade than a small creek. I know of none but the San Pedro and the Santa Cruz—the latter but a rivulet, losing itself in the sands near the Gila—the other but a diminutive stream, scarcely reaching that river. At the head-waters of the Concho, therefore, begins that great desert region, which, with no interruption save a limited valley or bottom-land along the Rio Grande, and lesser ones near the small courses mentioned, extends over a district embracing sixteen degrees of longitude, or about a thousand miles, and is wholly unfit for agriculture. It is a desolate, barren waste, which can never be rendered useful for man or beast, save for a public highway.”—Bartlett’s Personal Narrative, vol. i. p. 138.

Turning now to Central and Upper California, and 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 versâ. 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.

Fig. 3.

IN SUMMER.

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 annexed diagrams by the shading will show the situation of the rainy belts which cover Mexico, Utah, New Mexico, and California in summer and winter, and that the belts of rains are entirely distinct and different in character.

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.”

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 contiguity of the oceans? Obviously this is not 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 local 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.

Before proceeding to an examination of this connected atmospheric machinery, and an investigation of the particular ocean from which our rivers return, it may be well to look at the form in which they appear to return, that we may have a clear understanding of terms.

They seem to return in the form of clouds, and in storms and showers, although, in truth, they return in regular, 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.

The term storms, seems to be used by European meteorologists to denote what we term thunder showers or gusts, and tornados; while what we call storms are denominated by them regular rains. As the terms are extensively in use in this country, we must adhere to the meaning attached to them here rather than there.

Storms with us, then, are regular rains of from six to forty-eight or more hours’ continuance: generally without lightning, or thunder, or gusts, and usually with wind of more or less force, from some easterly point. They are called north-east storms, or south-east storms, according to the point from which the surface winds blow. Practically we shall find that this distinction is of some importance, for the north-east storms are the longest, lasting generally twenty-four hours, or more, while the south-east ones seldom, if ever, continue as long.

These storms extend over a considerable surface, rarely less than one hundred miles in one direction or another, and sometimes fifteen hundred, or more. Distinct showers cover but a small surface, sometimes not more than forty to one hundred rods, as in the tornado, and rarely more than ten 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 thirty to one hundred and fifty 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, every where 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 cumulus, we have very much as they have in Europe, and doubtless as they exist every where outside of the tropics. The nimbus, another cloud described by him, is not distinct from the cumulus or stratus. An isolated, limited thunder-shower in a clear sky, presents the appearance of a nimbus, as shown in the cuts, but the basis of it is a cumulus, and it differs from an ordinary fair-weather cumulus merely in the dark and fringe-like appearance of the rain as it is falling from its lower surface, and sometimes in the existence of a stratus above and in connection with it. A similar form is often assumed by the peculiar clouds of the N. W. winds in March or November, when they assume the form of squalls, and drop flurries of snow. The nimbus, therefore, is not a distinct cloud, but an appearance which the cumulus, stratus, or cirro-stratus has in a stormy or showery state, and does not deserve a distinct name. It is but a cumulus, or a stratus, or cirro-stratus dissolving in snow or rain. It is important that this term should be abandoned. It tends to confuse and prevent a clear understanding of the difference in the character of the clouds, and in relation to which precision is both difficult and desirable.

The figures on pages 27 and 29, show the different kinds of clouds as designated by Howard. They are copied from the engravings in the sixth edition of Maury’s “Sailing Directions.”

Fig. 5.

[Larger Image]

Fig. 6.

[Larger Image]

How far these representations correspond with the actual appearance of the different compound forms in England, I can not say. But although they convey a general idea, they are not sufficiently accurate for practical illustration or observation here. Indeed Howard himself has omitted from his last edition his plate of the clouds, assigning as a reason, “that the real student will acquire his knowledge in a more solid manner by the observation of nature, without the aid of drawings, and that the more superficial are liable to be led into error by them.” The collection of forms in the cuts does not contain some very important ones, and contains some which are not distinct forms; but they may aid us somewhat in this inquiry, and, therefore, I have copied them. It is well, also, for the reader to have the generally received description before him.

But for the purpose of practical illustration hereafter, and greater precision, I shall follow a somewhat different order in describing them, and introduce two forms of scud quite as important, practically, as any other.

First, then, commencing at the earth, we have what may be properly termed fog, or low fog. This forms, in still clear weather, in the valleys, and over the surface of the rivers and other bodies of water, during the night, and most frequently the latter part of it, and is at its acmé at sunrise, or soon after, limiting vision horizontally and perpendicularly, and dissolving away during the forenoon. It is rarely more than from two to four hundred feet in height at its upper surface, and often much less, and is composed of vesicular condensed vapor, sometimes sufficiently dense to fall in mist, and is doubtless in composition substantially what the clouds are in the other strata of the atmosphere, as observed by us, or passed through by aeronauts. I have never seen it carried up to any considerable height into the other strata by any of the supposed ascending currents, to form permanent clouds, and shall have occasion to allude to the fact in another connection. It disappears usually before mid-day, and has, when thus formed, no connection with any clouds which furnish rain.

To this Dr. Howard originally gave the name of stratus, and so it is represented upon the cut; but the latter term may be with greater propriety applied to the smooth uniform cloud in the superior strata from which the rain or snow is known to fall, and I shall retain and so apply it.

The next in order, ascending, is high fog. This is usually from one to two thousand feet in height at its lower surface. It forms, like low fog, during the night and in still weather; and is rarely, if ever, connected with clouds which furnish rain. It breaks away and disappears between ten and twelve in the forenoon, usually passing off to the eastward. This fog is most commonly seen in summer and autumn, particularly the latter, and unless distinguished from cloud will deceive the weather-watcher. It is readily distinguishable. Although often very dense, obscuring the light of the sun as perfectly as the clouds of a north-east storm, it differs from them. It forms in still clear weather, is present only in the morning, is perfectly uniform, and, before its dissolution commences, without breaks, or light and shade, or apparent motion, and unaccompanied by scud or surface wind. The storm clouds are never entirely uniform, or without spots of light and shade, by which their nature can be discerned, and rarely, when as dense as high fog, without scud running under them and surface winds.

There is another fog still, connected with rain storms, but it does not often precede them; occurring at all seasons, but most commonly in connection with the warm S. E. thaws and rains of winter and spring; and which usually comes on after the rain has commenced and continued for awhile, and the easterly wind has abated; occupying probably the entire space from the earth to the inferior surface of the rain clouds or stratus. Practically this does not require any further notice. It is an incident of the storm. When formed it remains while the storm clouds remain, and passes off with them. It is sometimes exceedingly dense in February and March, when it accompanies a thaw, and if there is a considerable depth of snow, it has the credit of aiding essentially in its dissolution.

Mingled with the smoke of London, it produced there the memorable dark day of the 24th of February, 1832, and at various other times has produced others of like character. (See Howard’s Climate of London, vol. iii. pp. 36, 207, 303.) These fogs have been so dense there that every kind of locomotion was dangerous, even with lanterns, at mid-day.

The next in order, ascending, are the storm scud, which float in the north-east or easterly, south-east or southerly wind, before and during storms.

These, as the reader will hereafter see, are, practically, very important forms of cloud condensation—although they have found no place in any practical or scientific description given of the clouds, and are not upon the cuts. They are patches of foggy seeming clouds of all sizes, more or less connected together by thin portions of similar condensation, often passing to the westward, south-westward, north-westward, or northward with great rapidity. Their average height is about half a mile, but they often run much lower. They are usually of an “ashy gray” color. The annexed cut shows one phase of them, from among many taken by daguerreotype. The arrows pointing to the west show the scud distinguished from the smooth partially formed stratus above. This view was taken a few hours prior to the setting in of a heavy S. E. rain storm. It is a northerly view.

Fig. 7.

At about the same height, but in a different state of the atmosphere, float the peculiar fair-weather clouds of the N. W. wind. They usually form in a clear sky, and pass with considerable rapidity to the S. E. Sometimes they are quite large, approaching the cumulus in form, and white, with dark under surfaces, and at others, in the month of November particularly, are entirely dark, and assume the character of squalls and drop flurries of snow; and then resemble the nimbus of Howard. They assume at different times and in different seasons, different shapes like those of the scud, the cumulus, or the stratus.

Fig. 8.

They form and float in the peculiar N. W. current which is usually a fair-weather wind, and are never connected with storms. In mild weather they are usually white, and in cold weather sometimes very black, and at all times differ in color from the ashy gray scud of the storm. This variety is not represented upon the general cuts. The annexed diagram shows one phase of them, but they are readily observable at all seasons of the year, when the N. W. wind is prevailing; differing in appearance according to the season. Let these, as well as the storm scud, be carefully observed and studied by the reader, and let no opportunity to familiarize himself with their appearance be lost. A brief glance at each recurrence of easterly or north-westerly wind will suffice.

SUMMER CUMULI.

The cumuli appear in isolated clouds of every size, or in vast clouds composed of aggregated masses, as the peculiar cloud of the thunder shower. They form as low down as the scud or fair-weather cloud of the N. W. wind, which, for convenience, I will call N. W. scud; and often in violent showers, and particularly in hail storms, extend up as far as the density of the atmosphere will permit them to form. Professor Espy thinks he has measured their tops at an altitude of ten miles. Others have estimated their height, when most largely developed, at twelve miles; but it is very doubtful whether the atmosphere can contain the moisture necessary to form so dense a cloud at that elevation. It is their immense height, however, whether it be six, or eight, or ten miles, together with the sudden and violent electric action, condensing suddenly all the moisture contained in the atmosphere within the space occupied by the cloud, which produces such sudden and heavy falls of rain or hail. As the rain drops or hail, when formed at such an elevation, in falling through the partially condensed vapor of the cloud must necessarily enlarge by accretion from the particles with which they come in contact, and probably also by attraction, their size when they reach the earth, though frequently very considerable, is not a matter of astonishment. The cumulus is represented in the general plate with sufficient accuracy to show its peculiar character.

In summer, when the air is calm, the weather warm, and no storm is approaching, there is always, in the day time, a tendency to the formation of cumuli. This tendency exhibits itself about ten o’clock in the forenoon, and they gradually form and enlarge until about two in the afternoon; and after that, if they do not continue to enlarge and form showers, they melt away and disappear before nightfall. Sometimes in July and August the atmosphere will be studded with them at mid-day, floating about three-quarters of a mile from the earth (in a level country), gently and slowly away to the eastward. At times it may seem as if they must coalesce and form showers, yet they frequently do not, but gradually melt away, as before stated.

The cumulus is the principal cloud of the tropics, and is not often seen with us except in summer, or when our weather is tropical in character.

The engraving on the preceding page, shows a phase of these fair-weather summer cumuli.

The last in order occupying (with their compounds) the higher portions of the atmosphere, are the cirrus and stratus. The cirrus is often the skeleton of the other, and precedes it in formation.

These are the proper clouds of the storm, in our sense of the term. While, however, the cirrus remains a cirrus, it furnishes no rain. When it extends and expands, and its threads widen and coalesce into cirro-stratus and stratus, or it induces a layer of stratus below it, the rain forms.

The following is Dr. Howard’s description of cirrus: “Parallel, flexuous or diverging fibers, extensible by increase in any or in all directions. Clouds in this modification appear to have the least density, the greatest elevation, and the greatest variety of extent and direction. They are the earliest appearance after serene weather. They are first indicated by a few threads penciled, as it were, on the sky. These increase in length, and new ones are in the mean time added to them. Often the first-formed threads serve as stems to support numerous branches, which in their turn, give rise to others.”

The illustrations in the general cut are imperfect, and do not represent the delicate fibers of the cloud, for it is a difficult cloud to daguerreotype or engrave, but the representation is sufficiently accurate to give the reader a general idea of the different varieties, and enable him to discover them readily by observation. They are the most elevated forms, always of a light color, and often illuminated about sunset by the rays of the sun shining upon their inferior surface; the sun, however, often illuminates, in like manner, the dense forms of cirro-stratus, and the latter, from their greater density, are susceptible of a brighter and more vivid illumination.

The stratus is a smooth, uniform cloud—the true rain cloud of the storm; often forming without much cirrus above, or connected with it. It may be seen in its partially formed state in the bank in the west, at nightfall, or in the circle around the moon in the night. When it becomes sufficiently condensed, rain always falls from it, but in moderation. If there be large masses of scud running beneath it for its drops to fall through (especially as is sometimes the case, in two or more currents), the rain may be very heavy. But more of this hereafter.

Fig. 10.

The annexed cut shows the forming stratus, light and thin, passing to the east, as indicated by the short arrows just before a storm, while the scud beneath is running to the west.

It was copied from a daguerreotype view, facing northwardly.

Intermediate between the fibrous, tufted, cirrus, and the smooth uniform stratus, there is a variety of forms partaking more or less of the character of one or the other, and termed cirro-stratus. No single correct representation of cirro-stratus as a distinct cloud, can be given—but several varieties will be hereafter alluded to, under the head of prognostics. Several modifications are represented with tolerable accuracy upon the cuts.

The cirro-cumulus is a collection in patches of very small distinct heaps of white clouds; they are called fleecy clouds, from their resemblance to a collection of fleeces of wool, and are imperfectly represented on the general cut. They do not appear often, and are usually fair-weather clouds.

This form has none of the characteristics of the cumulus, and does not appear in the same stratum. It was probably called cumulus because its small masses are distinct, as are those of the ordinary cumulus. It occurs in the same stratum as cirro-stratus, and properly belongs to that modification. I retain the name inasmuch as the cloud is of some practical importance.

The cumulo-stratus is seldom seen in our climate, as it is represented in the cut. Stratus condensation above, and in connection with cumulus condensation, is not uncommon, but that precise form is rare.

This, too, is practically of no consequence, and I shall take no further notice of it.

Recapitulating, I give (in a tabular form) the three principal strata and their modifications, located with sufficient accuracy for illustration. The clouds which are found in an upper or lower portion of a stratum are so represented by the location of their names; those which appear at all heights in the stratum, with the names across. The elevation is the average one—although there is no limit to the cirrus above, except the absence of sufficient moisture. It was seen by Guy Lussac, and has been by other aeronauts, at an elevation of five miles, or more, when too delicate to be visible below.

With the assistance of this table of elevations, and a careful observation, the reader can soon become familiar with the forms of clouds and their relative situations.

CHAPTER III.

Having thus taken a brief view of the different clouds, let us return to the inquiry, from what ocean, and by what machinery, our “rivers return.”

Not wholly or mainly from the North Atlantic, although it lies adjacent to us, and they often seem to do so; for, first, all storms, showers, and clouds, which furnish, independently, any appreciable quantity of rain to the United States, and even adjacent to the Atlantic, or indeed to the Atlantic itself, come from a westerly point, and pass to the eastward. This is a general, uniform, and invariable law, although there is in different places, and in the same place at different times, some variation in their direction; ranging in storms from W. by S. to S. S. W., and in showers between S. W. and N. W., to the opposite easterly points of the compass; the most general direction, east of the Alleghanies, being from W. S. W. to E. N. E.

But do we not see, you inquire—at least those of us who live east of the Alleghanies—that when it rains, the wind is from the eastward; and that the clouds follow the wind from the east to the west? You do indeed, generally, in all considerable storms, observe that the wind blows from some easterly point, and that seeming clouds are blown by it to the westward; but what you see, and call clouds, are not the clouds which furnish the rain. Far above the seeming clouds you notice, directly over your head when it rains or snows, are the rain or snow clouds, dense and dark, passing to the eastward, how strong soever the wind may blow from the quarter to which they tend, or any other quarter, between you and them. What you see below them are scud. So the sailors call them, and so I have termed them. It is a “dictionary name,” and a good one, expressive of a distinction between them and clouds. They are thin, and the sun shines through them, although with some difficulty, when the rain clouds above are absent or broken. This east wind and the scud are not the storm, or essential parts of it. Storms occasionally exist, particularly in April, without either. They are but incidents, useful, but not necessary incidents, as all surface winds are.

If you could see a section of the storm, you would see the rain cloud above, moving to the east, and the scud beneath running to the west, as indicated by the arrows in the cut on page [40]. Opportunities frequently occur when these appearances may be seen. Storms are sometimes very long, a thousand miles, perhaps, from W. S. W. to E. N. E., and not more than one to three hundred miles wide from S. E. to N. W., and their sides, particularly the northern ones, regular, and without extensive partial condensation. Then the storm cloud above, moving to the eastward, and the scud running under to the westward, may be seen as in the cut.

So they may be seen before, at the commencement, and at the conclusion of easterly storms, in a majority of cases, and the reader is desired to notice them particularly as opportunities occur.

The term running, too, is a very expressive one, used by sailors as applicable to scud. For while the forming or formed storm clouds may be moving moderately along, at the rate of twelve to fifteen or twenty miles an hour, from about W. S. W. to E. N. E., the scud may be running under them in a different direction—opposite, or diagonal, or both—at the rate of twenty, fifty, sixty, and, in hurricanes, even ninety miles an hour. You have doubtless seen these scud running from N. E. to S. W., and without dropping any moisture, a day or sometimes two days, before the storm coming from the S. W. reached the place where you were; and then, sometimes the storm cloud slipped by to the southward, and the expected storm at that point proved “a dry northeaster.” Sometimes the condensation, although sufficiently dense to influence and attract the surface atmosphere, and create an easterly wind and scud, does not become sufficiently dense to drop rain, and then, too, we have a dry northeaster, which may melt away or increase to a storm after it has passed over us. I have never seen, except, perhaps, in a single instance, one of these masses of scud, however dense, which had not a rain (stratus) cloud above it, drop moisture enough to make the eaves run. So you see it may be true, and if you will examine carefully, you may satisfy yourself that it is true, that the storms all move from a westerly point to the eastward, notwithstanding the wind under them is blowing, and the scud under them are running to the westward.

There are many other methods by which the reader may determine this matter himself. He may catch an opportunity for a view, when there is a break in the stratus cloud above, and the sun or moon, no longer obscured by the storm cloud, shines through the scud beneath. Then he may see they are moving in different directions. The upper cloud, if there be any of it left, always to the eastward.

Again, we may see the storm approach from the westward, as it often does, before the wind commences to blow, and the scud to run from the eastward; particularly snow storms in winter, and the gentle showers and storms of spring.

Again, thunder storms, we know, come from the westward, and apparently against an east wind. It is sometimes said they approach from the east, but it is a mistake. During thirty years attentive observation in different localities, I have never seen an instance. They sometimes form over us, or just east of us, or one may form at the east and another at the west, and as they spread out in forming, one may seem to be coming from the east, or there may be an easterly current, with dense flocculent scud at the under surface of the shower cloud running westward, but they finally pass off to the eastward, and never to the westward. It is possible that a patch of scud may become sufficiently dense and electrified to make a shower, but I have never observed one. Such an apparent instance may be found recorded in “Sillman’s Journal,” vol. xxxix. page 57. I have seen the scud assume a distinct cumulus form, but never to become sufficiently dense to make a thunder shower.

Thunder and lightning sometimes attend portions of regular storms in spring and autumn, but the thunder is always heard first in the west, and last in the east.

Again, there are admitted facts with which you are conversant, which prove this proposition. When it has been raining all day, and just at night the storm has nearly all passed over to the eastward, and the sun shines under the western edge of it, and “sets clear,” as it is termed—you say that “it will be clear the next day.” Why? Because the storm will not pass to the westward, covering the sun and continuing, how strong soever the wind may be from the east; and because it is passing, and will continue to pass off to the eastward, leaving the sky clear. The easterly wind will stop as soon as the storm clouds have passed, and it will fall calm, or the wind will “come out” from the westward.

So, too, when the clouds are dark in the west in the morning, and the sun rises clear, but “goes into a cloud,” as it is expressed, you say that it will rain. And if the clouds are dense this generally proves true; because there is a storm or shower approaching from the west, and passing over to the east, the western edge of whose advance condensation has met the sun in his coming, and obscured him from your vision.

When, too, it has been storming, and lights up in the N. W. you say it will clear off; the N. W. wind will blow all the clouds away. It is, indeed, generally true that when it so lights up it is about to clear off; although it sometimes shuts down again, in consequence of the approach of another storm from the westward, following closely behind the one which is passing off. It is a great mistake, however, to suppose the N. W. wind blows away the clouds. Watch the smooth stratus rain cloud at its lower edge, where the clear sky is seen, and you will see that it is moving on steadily to the N. E., in obedience to the laws of its current, and will do so, even when its retreating edge has passed up to the zenith, and down to the S. E.

The storm uncovers us from the N. W. by the contraction of its width, or because it has a southern lateral extension and dissolution, and not by being blown away by the N. W. wind; although that wind, by its peculiar fair-weather clouds, may be, perhaps, observed beneath, ready to follow its retreating edge.

Again, when it has been clear all day, and the sun sets in a bank of cloud, you say—“it will rain to-morrow, the sun did not set clear,” and unless that bank is a thunder cloud, merely, which will pass over or by you, with or without rain, before morning, it is generally true that it will. The bank will prove the eastern edge of an approaching storm.

From these generally admitted and understood facts, you may know that storms pass from the west to the east.

This proposition is also proved by all the investigations of storms, which have taken place since the settlement of this country. Storms of great severity attract particular attention, and are said to “back up” against the wind, because they are observed to commence storming first at the westward, although the wind is from the eastward. Doubtless you recollect many such instances recorded in the newspapers. No season occurs without such notices.

Many storms have been investigated by Mr. Redfield, for the purpose of sustaining his theory. Many others by Professor Espy, to sustain his. One by Professor Loomis, with great research and ability—and some by others, accounts of all which have been published; and every one yet investigated, north of the parallel of 30°, has been shown to pass from a westerly to an easterly point.

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° 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° and 44° 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.

Between the parallels of 35° north latitude, and 35° south latitude—changing its location within this limit at different seasons of the year—encircling the earth, and covering about one-half of its area—we find the trade-wind region. In this region are the simple and uniform arrangements, which extend every where, and produce all the atmospheric phenomena. In the center of it we find that movable belt of continual or daily rains, and comparative calms, particularly near its center, about four hundred and fifty miles in width upon the Atlantic, and over Africa, and the eastern portions of the Pacific, and something more over South America and the West Indies, the western portion of the Pacific and the Indian Ocean, to which we have already alluded. This belt of rains and calms follows the trades and sun, in their transit north and south, from one tropic to the other—its width and extension depending upon the volume of trade-winds existing on the sides of it. Its southern edge, when the sun is at the southern solstice, extends to 7° south in the Atlantic, to 10° south in the Indian Ocean, and still further, probably, over South America: on this point I do not pretend to be accurate, for accuracy is not essential. When the sun is at the northern solstice the southern edge is carried up as far as 12° north, over the Atlantic, and still further over the northern portions of South America, the West Indies, and Mexico. It travels, therefore, from south to north, over from twenty to forty degrees of latitude. The presence of this belt of rains over any given portion of the inter-tropics, gives that portion its rainy season, and its absence, as it moves to the north, or the south, gives the portion from which it has moved, its dry season. It passes in its transit twice each year over some portions of the country, Bogota, for instance, and two corresponding rainy and dry seasons result. Its presence, and character, and movements, are as fixed and regular, over from twenty-five to forty degrees of the earth’s surface, and all around it, as the presence and movements of the sun over the same area.

At the northern edge of this movable belt of rain, and extending in some places, particularly in the Pacific Ocean, north about 20°, or about one thousand four hundred miles, and in other places a less distance, the N. E. trade winds prevail, blowing toward and into it from N. N. E., N. E., and E. N. E., averaging about N. E. At the south line of this belt of rains, extending south from twenty-five to thirty degrees, or from sixteen hundred to two thousand miles, the S. E. trades blow toward and into it, from the S. E., S. S. E., or E. S. E., averaging about S. E. Of course the northern limit of the N. E. trades travels north and south with the belt of rain, toward which it blows; and so the southern limit of the S. E. trades travel in like manner with the rainy belt, or rather, to speak with entire accuracy, the belt of rain moves with the trades, and the trades follow the verticality of the sun. The following diagrams exhibit approximately, and with sufficient accuracy for illustration, the situations of the rainy belt and the trades, when at their northern and southern limit, as well as the manner in which it must give certain localities two rainy seasons each year, in its transit north and south.

At the northern and southern limits of the trade-winds, and extending from them to the poles, are found the variable winds and irregular extra-tropical rains, all over the earth, which are shown by the shading on the maps. This line of extra-tropical rains descends to the south, following the retreating trades as they descend in our winter, and recedes north before the trades when they return in spring and summer, so that at the outer limit of the trades respectively, toward the poles, the line of extra-tropical rains will be found, receding or following that limit, as the trades pass up and down with the sun. From the north pole to the northern limit of the N. E. trade-winds, wherever found, whether at 38° north latitude, as in some places in summer when the sun is at the tropic of Cancer; or whether at 20° to 30° north latitude, as in our winter, when the sun is at the tropic of Capricorn; the extra-tropical rains prevail. A state of things precisely similar exists between the south pole and the southern limit of the S. E. trades. Between this northern limit of the N. E. trades and the northern line of the inter-tropical belt of rains, wherever situated (with two exceptions, to which we have alluded and shall allude again), there is, for the time being, a dry season; and a like dry season between the southern line of the belt of rains and the southern limit of the S. E. trades. We have, therefore, extending around the earth, a belt of daily tropical rains, near the center,—two belts of drought which are mainly trade-wind surfaces, one on each side of the central rainy belt,—extending to the outward limits of the trades and the line of extra-tropical rains; and these rainy and dry belts, moving up and down after the sun, a distance of from twenty to forty degrees of latitude, each year.

Fig. 10.

IN SUMMER.

Fig. 11.

IN WINTER.

Such are the main phenomena, at the surface, in the trade-wind region. Ascending a step higher in the atmosphere, we find, above the surface-trades, a counter-trade, running, not in the opposite direction, but at right angles, or nearly so. The counter-trade which issues from the northern side of the rainy belt, running to the N. W. or W. N. W., and the counter trade which issues from the southern side, running to the S. W. or W. S. W., varying, as the trades do in direction in different localities. These counter-trades are continuations of the surface trades, which, ascending in their course, have threaded their way through the opposite trade in the rainy belt, and are continuing on at the same angle, and in the same direction at which they blew upon the surface, and in obedience to the same law. This is apparent from several considerations.

1st. They issue at the same angle, and over the top of the surface trades. In the West Indies and elsewhere, this has been ascertained and proved by the course of the storms, and the rotation of their surface winds, and observation.

2d. We can not suppose the N. E. trade to be reflected, and turn back over itself at a right angle. That would be impossible, even if there were a wall of solid material there for it to blow against. Air is a peculiar fluid, and it stratifies with astonishing ease. He who supposes that a current of air put in motion can be turned aside by another current, or by the atmosphere at rest, or can be made to mingle, is mistaken. It will stratify, and force itself onward through the adjacent and opposing atmosphere, and in a right line. I have observed some remarkable instances of this character.

3d. The cause which operates to produce the surface trades, still operates upon the current to carry it over into the other hemisphere; a counter-trade, as we shall see. It is impossible, therefore, to believe that the surface-trades as they arrive at the belt of rains and calms, turn at a right angle, or at any angle, and return: and impossible to doubt that they pass through each other in this belt, and out at the opposite side, as upper currents, at the same angle at which they entered. Of course the N. E. trade of the Atlantic becomes the N. E. counter-trade of South America, carrying their storms in a S. W. direction, and the S. E. trade of the Atlantic the S. E. counter-trade of the West Indies, carrying all their storms in a N. W. direction; and what is true of them is true of the trade winds every where, all over the globe, over the land and over the sea.

Doubtless here some one will say, our upper current is a S. W. current. True, the S. E. trade which enters the belt of rains, and issues out on the north, a S. E. upper current or counter-trade, keeps that course until it arrives at the northern limit of the surface trade, when, in obedience to another law, which we shall notice, it gradually decends near the surface, curves to the eastward, and becomes the S. W. current which passes over us. And so we have the S. E. trade-wind of the South Atlantic, with its moisture, warmth, electricity, and polarity, over, and perhaps sometimes around us, dropping the electric rain which makes glad our fields; giving us, when not prevented by other conditions, the balmy air of spring, the Indian summer of autumn, and the mild mitigating changes of winter; and thus, our rivers, which run into the sea, return to us again.

But let us go back to the trade-wind region—the region of regularity and uniformity—and examine somewhat more attentively its features, that we may more fully understand the character of this counter-trade.

Here are 60° at least of the 180° of the earth’s surface, and at its largest diameter, covered in the course of the year, and of their travels, by the trade-winds at the surface, the counter-trades above, and the belt of rains and comparative calms, formed by the action of the opposite trades, as they thread their way through each other, to assume the relation of counter-trades. Truly the magnitude, simplicity, and regularity of this machinery are most wonderful.

There are, however, some apparent anomalies which deserve attention. Here are most distinctly marked the rainy and dry seasons, existing side by side. Here are the rainless portions of the earth, already but briefly alluded to; here the monsoons, and another peculiarity, viz.: the gathering of the counter-trades upon the western sides of the two great oceans, into two aerial currents of greater volume, analogous somewhat to the two gulf streams of those oceans. Let us examine these anomalies.

The rainy and dry seasons depend, as we have seen, upon the transit north and south of the rainy belt, or belt of comparative calms. Wherever this belt may happen on any given day to be situated, each side of it the trades prevail, it is dry, the earth is parched, and vegetation withers. These changes are graphically described by Humboldt in his “Views of Nature,” as they occur on the northern portions of South America, as follows: “When, beneath the vertical rays of the bright and cloudless sun of the tropics, the parched sward crumbles into dust, then the indurated soil cracks and bursts, as if rent asunder by some mighty earthquake. The hot and dusty earth forms a cloudy vail, which shrouds the heavens from view, and increases the stifling oppression of the atmosphere; while the east wind (i. e. trade-wind), when it blows over the long heated soil, instead of cooling, adds to the burning glow.

“Gradually, too, the pools of water, which had been protected from evaporation by the now seared foliage of the fan-palm, disappear. As in the icy north animals become torpid from cold, so here the crocodile and the boa-constrictor lie wrapped in unbroken sleep, deeply buried in the dried soil. Every where the drought announces death, yet every where the thirsty wanderer is deluded by the phantom of a moving, undulating, watery surface, created by the deceptive play of the reflected rays of light (the mirage). A narrow stratum separates the ground from the distant palm-trees, which seem to hover aloft, owing to the contact of currents of air having different degrees of heat, and therefore of density. Shrouded in dark clouds of dust, and tortured by hunger and burning thirst, oxen and horses scour the plain, the one belowing dismally, the other with outstretched necks snuffing the wind, in the endeavor to detect, by the moisture in the air, the vicinity of some pool of water not yet wholly evaporated.

“Even if the burning heat of day be succeeded by the cool freshness of the night, here always of equal length, the wearied ox and horse enjoy no repose. Huge bats now attack the animals during sleep, and vampyre-like suck their blood; or, fastening on their backs, raise festering wounds, in which mosquitos, hippobosces, and a host of other stinging insects, burrow and nestle. Such is the miserable existence of these poor animals, when the heat of the sun has absorbed the waters from the surface of the earth.

“When, after a long drought, the genial season of rain arrives, the scene suddenly changes. The deep azure of the hitherto cloudless sky assumes a lighter hue. Scarcely can the dark space in the constellation of the Southern Cross be distinguished at night. The mild phosphorescence of the Magellanic clouds fades away. Even the vertical stars of the constellations Aquila and Ophiuchus, shine with a flickering and less planetary light. Like some distant mountain, a single cloud is seen rising perpendicularly on the southern horizon. Misty vapors collect and gradually overspread the heavens, while distant thunder proclaims the approach of the vivifying rain. Scarcely is the surface of the earth moistened, before the teeming steppe becomes covered with Killingiæ, with the many-panicled Paspalum, and a variety of grasses. Excited by the power of light, the herbaceous Mimosa unfolds its dormant, drooping leaves, hailing, as it were, the rising sun in chorus with the matin song of the birds, and the opening flowers of aquatics. Horses and oxen, buoyant with life and enjoyment, roam over and crop the plains. The luxuriant grass hides the beautiful and spotted jaguar, who, lurking in safe concealment, and carefully measuring the extent of the leap, darts, like the Asiatic tiger, with a cat-like bound on his passing prey.”

Such is Humboldt’s description of the dry season on the Orinoco, and the return of the belt of rains from the south.

Again, within this trade-wind region are the rainless countries. These are portions of the earth which the equatorial rainy belt does not ascend far enough north in summer to cover, nor does the southern edge of the extra-tropical regular rains descend, in winter, far enough south to cover them, and where, of course, rain seldom, if ever, falls. Such are the central parts of the Desert of Sahara, Egypt, Arabia, portions of Affghanistan, Beloochistan, and the western parts of Hindoostan, to the north of the inter-tropical belt, and a similar state of things exists south of the equator in parts of South America, Africa, and New Holland, although upon a comparatively small surface.

Again, another anomaly is the gathering of the trade winds into greater volumes, on the westerly side of the great oceans, and the consequent carrying of the equatorial rainy belt up to the region of extra-tropical rains, on the eastern side of the great continents of Asia and North America, and the peculiar liability of these aerial gulfs to hurricanes and typhoons. Such an aerial gulf gathers over the Caribbean Sea, and the West Indies. Passing across the Gulf of Mexico, it enters over Texas, and Louisiana, and the other southern states; its western edge passing north in autumn and winter, on the eastern side of the highlands of Western Texas, New Mexico, and the Great Desert; curving, as all counter-trades do, to the eastward as soon as it passes the limit of the N. E. trades, and spreading out over our favored country, leaving the evidence of its pathway in the greater quantities of rain, which fall annually upon its surface. This gathering deprives a portion of the Atlantic, north of the tropics, of its share of the counter trade, and there, as every where, where the volume of counter-trade is small, storms and gales are infrequent, and of less force, and comparative calms prevail. That portion of the Atlantic has long been known as “the horse latitudes,” a name given to it by our Yankee sailors, because, there, in former times, the old-fashioned, low-decked, flat-bottomed, horse-carrying craft of New England, bound for the West Indies, often floundered about in the calms and baffling winds, until their animals perished for want of water, and were thrown overboard. Lieutenant Maury, in his most praiseworthy and exceedingly useful investigation of “The Winds and Currents of the Ocean,” has defined the situation of these calms and baffling winds at different seasons—for they move up and down, of course, with the motion of the whole machinery—and enabled navigators to avoid them, by running east before they attempt to make southing; and very materially shortened the voyages to the equator.

A like gathering, in volume, of the S. E. trade, on the western side of the Pacific, enters over Asia, and covers China and Malaysia, extending, in its western course, nearly as far as the western edge of Hindoostan. In this concentrated volume of counter-trade, and owing to its concentrated action, form and float the typhoons of the China Sea, and of the Bay of Bengal; and to this anomalous aerial gulf stream, the S. E. portions of Asia, from the western desert of Hindoostan, to the eastern portion of China, north of the rainy belt, owe their great supply of moisture and fertility, and their peculiar climate. The western line of this volume of counter-trade is marked by the eastern portion of the rainless region of Beloochistan, and the north-western deserts of India, as the western edge of our concentrated volume of counter-trade, is marked by the arid plains of northern Mexico, western Texas, and New Mexico. On the south of the equatorial rainy belt, there is no corresponding aerial gulf of equal volume, as there is no corresponding gulf stream of equal magnitude. On the western side of the Indian Ocean we find a gathering of the N. E. trades from the Bay of Bengal and the Indian Ocean, in which form and travel the hurricanes which prevail—traveling to the southward and westward—about the Isle of France or Mauritius; and the lagullus oceanic current, which runs down to the S. W. toward the Cape of Good Hope. But the extension of South America to the eastward, under, or just south of the N. E. trades, does not permit the formation of such a concentrated volume on the western side of the Atlantic, nor is the strength or regularity of the N. E. trades, on that ocean, equal to those of the S. E.

Nor is the magnetic intensity on the eastern and middle portions of the Pacific, sufficient to produce such a concentration, in large volume, there. The trades over that ocean, therefore, curve without concentration, except a partial one, over the western groups of Polynesia, which the Asiatic line of magnetic intensity approaches and where hurricanes are sometimes found, until we arrive near the eastern line of magnetic intensity, on the eastern side of Asia. We shall, hereafter, have occasion to follow the anomalous concentrated volumes of the S. E. counter-trade, of the northern tropic, on the western side of the great oceans, in explanation of some of the phenomena which we find north of the trade-wind region. Suffice it here to add, that if it were not for the concentration of these counter-trades, on the western side of the great oceans, the rainless region between the parallels of 20° and 30° would encircle the earth; and China and the Eastern United States would have a distinctly marked rainy and dry season, as have California, the Barbary States, Syria, Persia, and other countries which lie north of the rainless region, within the summer range of the N. E. trades, but also within the winter descending range of the belt of extra-tropical rains.

Another anomaly which we find in the trade-wind region, is the monsoon. There are several of them, but they are found, in the greatest strength and regularity, in the Indian Ocean. Another, defined by the investigations of Maury, is found on the west coast of Africa, extending out over the Atlantic. Another prevails on the western coast of South and Central America. The etesian winds of the Mediterranean are but the N. E. trades, whose northern limit is carried up in summer, by the transit of the connected machinery, to the north, over that sea. The N. E. and S. E. monsoons, so called, of the Indian Ocean, are but the regular trades, blowing when the belt of rains is absent, as they do all over the globe. The N. W. monsoon, south of the equator, in the vicinity of New Holland; the S. W. monsoon which blows from the Arabian Sea, in upon Hindoostan; the S. W. monsoon of the Atlantic, south of the Cape De Verde Islands; and the variable west monsoon winds of the west coast of Southern and Central America, and Southern Mexico (known under several different names, but chiefly by that of Tapayaguas), are all that deserve attention as such.

At first sight they appear to be anomalies, but the facts declare their character with perfect certainty. First, they are not continuous, like the trades, but prevailing winds, and are storm winds; they always blow toward a region, or portion of the ocean, covered at the time by clouds and falling weather.

Second, they do not blow upon, or toward, heated surfaces of land or water—i. e., toward the dry and parched surfaces, where the dry season prevails, or from adjoining cold waters on to warm surfaces, but toward the land or water situated under the rainy belt. They are therefore incident storm winds, (as our easterly winds are incident storm winds) of the rain clouds of the tropics. They blow in upon the land, under the belt of rains, while that belt with its daily cloud, and inducing electric action, is over it, and follow that belt in its transit north and south. They blow from the warm south polar current of the Atlantic, which flows N. W. from the coast of Africa, toward the inshore north polar current, which is there flowing south, but under the belt of rains. In the Indian Ocean they blow from the center of that ocean, and the Arabian Sea, toward the belt which hangs over Hindoostan, from the S. W.; and when the rainy belt travels south they still blow toward, and under it, from the Indian Ocean, but of course from the N. W. The heated character of the waters of the Indian Ocean and Arabian Sea, which receive no polar currents, but heated waters from the Persian Gulf, and from rivers which flow into the Bay of Bengal over the heated plains of a tropical country, explain this. So, too, the monsoon of the Atlantic Ocean, does not blow north of the Cape De Verde Islands,—where the heated surface of Sahara, burning with the rays of a vertical sun, has a temperature sometimes ranging from one hundred and forty to one hundred and sixty degrees—but remains under the rainy belt, drawn from the heated waters which flow up from the South Atlantic, and travels north as the rainy belt travels north in summer, and south to the Gulf of Guinea, as that travels south in winter. The same is true of the Pacific monsoon, the Tapayaguas, the least marked of all, which blows in during the rainy season upon the west coast of Southern Mexico, and of Southern and Central America. They are all incident rain or storm winds, blowing in upon the land, or on to a colder surface of different polarity, during the rainy season; and if it were possible to catch one of our north-easters, in its passage over our country to the eastward, and anchor it to the Alleghanies, “paying out” so to have it reach in part over the Atlantic, and keep it there in operation six months, we should have a continual easterly wind under it; a monsoon more strongly marked than the monsoons of the Indian, or Atlantic Oceans. The received theory in relation to them is a fallacy.

Recapitulating, then, all the phenomena, we have,—Surface-trades, blowing toward the center, passing through each other, and continuing on as upper or counter-trades; a belt of rains, with calms near the center, formed by the trades where they meet and pass through each other, which travels with them north and south following the sun; two belts of drought, following the belt of rains and the trades, and followed by the extra-tropical line of rains, as it travels with the trades and the rainy belt, leaving a part of the earth which the equatorial rainy belt does not travel far enough north, nor the extra-tropical line of rains far enough south to cover, and which is consequently a rainless region; the monsoons, which are but incidents of the rainy belt, and the gathered volumes of counter-trade, on the west of the two great oceans, which usurp the place of the N. E. trades, carrying the rainy belt up to the region of extra-tropical rain, and preventing the rainless region from encircling the earth.

Upon what cause do these great central phenomena, so vast, so regular, so wonderful, depend? What is the motive power of this connected atmospheric machinery, whose action and influence extend over the entire globe?

“Heat, heat,” say the text books, the Professors, the votaries of meteorology. “All these phenomena are owing to the heat of the sun. It heats the ocean and the earth—the air is thereby heated and rises, the cold air rushes in from below, then the ascended current rolls off each way at the top toward the pole, acquiring a westerly motion from the rotation of the earth, slipping away from under it, and a different, viz.: an easterly motion, after reaching the latitude of 30°, from the same rotation; and all the winds and disturbances of the atmosphere are produced in the same way. They are produced by the action of heated surfaces upon the adjacent atmosphere.”

This is the great theory of meteorologists, by which they attempt to account for the various atmospherical disturbances, of both tropical and extra-tropical regions.

The whole theory is a fallacy—it will not stand the test of a careful examination. The bases of the theory, which are assumed to be facts, are not so. The agent has not the power claimed for it. A heated surface, alone, never caused any considerable ascending current, or if it did, never produced a mile of wind. I repeat it, the theory and all incidental ones—the thousand explanatory and modifying theories, and hypotheses—the whole system—is without foundation in fact, and will not bear a critical examination.

Let us see if this language is stronger than the facts will warrant.

The theory assumes that both the land and water, under this central belt, where the air is supposed to be rising are materially hotter than the land and ocean are on either side of it. Now, how much hotter are the air and the land under the belt of rains and calms, upon Hindoostan, or Africa, or South America, where the former is supposed to be acquiring heat and expansion so rapidly, and to be ascending, than under, and in the dry belts on either side? None; it is cooler by the thermometer—much cooler.

The central belt of rains in midsummer over Africa, extends up as far as 17° north latitude, and perhaps further. North of this line over the whole surface of the desert, the Barbary States, a part of the Mediterranean, and some portion of Italy, the dry season extends, and from the entire surface the N. E. trade blow into the central belt.[1] Over the desert they all pass. Now this desert is a sea of sand, under a vertical sun, intensely heated, blistering the skin with which it comes in contact, and often acquiring a temperature of 150° to 160° of Fahrenheit. Under the central belt of rains neither the earth nor air exceed the temperature of 84°. And yet the hot air of the desert does not ascend, but blows into this cooler central belt; and when it is felt as it blows off the western coast by the mariner, or even in Guinea, when the belt of rains has gone south in winter, as it often is as the harmattan, it is suffocating and intolerable. There, then, not only is it untrue, that the land and the air over it under the rainy belt are hotter, but it is true that intensely heated air blows horizontally from the Desert of Sahara. Nay, as it will appear in the sequel, this hottest of all surfaces not only can not have a vortex, but it can not induce a monsoon, and scarcely a sea breeze. The same is true in a great degree of the surface, and the air over it, on either side of the supposed vortex of the rainy belt upon South America. See the description of Humboldt, already given, where the thermometer stood as high as 115° of Fahrenheit in the shade, while the N. E. winds, the regular trades, were blowing over the land. And it is equally true of Arabia, and indeed of every portion of the earth. There is not a spot upon the globe where the land and the air are cooler by the side of the central belt of rains, than under it. And the opposite is true every where upon the land.

How much hotter is the ocean and air under this supposed vortex? But little hotter than they are on the side where the sun is not vertical, and none on the other. Let us be a little more particular. The temperature of the Atlantic under the belt of rains in our winter, and on the south of the belt at the latitude of 3° south, and down to 9° or more south, is 82°. The air may range a degree, or possibly two, higher than the water at either point. On the north this difference is from nothing at the meeting of the trades and belt of rains, to about 4° at their northern limit. This is too trifling to be worth one moment’s consideration. It is less, far less than the difference between the water and air of the Gulf Stream which runs along our coast, and the adjoining waters and air over them. While on the south side of the belt of rains the difference is actually against the theory—and the same state of things is reversed in summer, when the sun is vertical at the north.

From the log of an intelligent shipmaster, found in the wind and current charts of Lieutenant Maury, I abridge the following, which will illustrate this. Captain Young in February, found the N. E. trades at about 17° north latitude, with the water at 75° and air at 76°, trade-wind N. E.

Here the air was seven degrees colder at the extreme limit of the N. E. trades than in the center of the belt of rains, as it is, usually, in mid-winter, but not in summer. On the other hand, after he left the region of calms and rains, where the water and air stood with almost entire uniformity at 82°, on the 3d of March, and for three days thereafter, during which he was in the S. E. trades with fair weather, the water was the same as under the supposed vortex, viz., 82°, and the air rose to 83° and 84°! This is demonstration.

I also take from a letter of Lieutenant Walsh to Lieutenant Maury, relative to the cruise of the “Taney” the following, showing the warmth of the Gulf Stream compared with the adjacent ocean.

“We first crossed the Gulf Stream on the 31st of October; we struck it in latitude 37° 22′, longitude 71° 26′ as indicated by the temperature of the water, which was as follows:

77° was the highest temperature found in crossing at this time.

Re-crossing it in May, in latitude 35° 30′, longitude 72° 35′, he found the water as follows:

79° being the highest temperature found.”

The average difference between the temperature of the water of the Gulf Stream and the adjoining ocean, at the line of division, is about ten degrees, increasing to more than twenty on approaching the coast, and within one hundred miles—a far greater difference than is ever found on the winter side of the inter-tropical rainy belt.

It is not only not so, then, that the surface of the ocean is materially warmer under the belt of rains than the adjoining surface under the trades, especially on the summer side, but if it were so, the trades would not be created thereby, any more than upon the Gulf Stream. And the opposite is true of the land where the line of calms, and rains, and drought meet, all around the globe. The fact assumed is therefore untrue. The hottest surfaces, even at the rainless portion, where there is no vortex, no storm, and no wind but the continual uniform N. E. horizontal trade-wind, never created, by reason of the heat alone, a mile of wind, a storm or shower.

But, again, the belt of calms, where the air is supposed to rise and create a suction which draws the trades on either side a distance of from one thousand to two thousand miles, an average of three thousand miles in all, at least, is not itself, on an average, over five hundred miles in breadth from north to south. What a wonder of meteorology is here!

With a breadth of five hundred miles, the rising of the atmosphere is supposed to be so rapid and of such immense volume that it draws the surface atmosphere, one thousand to fifteen hundred miles on one side and two thousand on the other, with a uniform steady velocity of twenty miles per hour. Is this vast suction found by the unlucky mariner who may be drawn within the vortex? Not at all. He finds no rapid suction there, but horizontal currents, not steady, indeed, like the trades, and sometimes calms at the center, but still the currents are there, and, except near the center, there as squalls, showers, and baffling winds and as monsoons.

Again, is there at the mouth of this vortex, or as you approach it, an increased rapidity in the trade corresponding to the magnitude of its influence? Does the trade become a hurricane as it approaches the spot where it is to supply the place of that which has suddenly “expanded by heat, and been forced to rise, boil over, and run off at the top in turn?” Not at all. It blows gently, even up to the very line of the rainy belt, and becomes squally and baffling, falls gradually calm near the center, or changes to a monsoon.

But, again, the belt of rains is so far from being a belt of calms strictly, that its monsoons in the Indian, Atlantic, and Pacific Oceans, at times, extend hundreds of miles out over the ocean. That of the Atlantic, triangular, with its base resting on Africa, according to Lieutenant Maury, extends sometimes almost to the coast of South America, a distance of one thousand miles, and thus under the supposed ascending vortex. Where is the great uprising suction during the prevalence of this extensive surface horizontal monsoon beneath it? Manifestly it does not exist. Nay, that monsoon is blowing from the warm current which sets up from the Cape of Good Hope toward the Caribbean Sea, and over the cold north polar current, which runs down between the continent and the Cape de Verdes. Equally untrue is the presumption that the air rises over heated portions of the earth elsewhere, and by reason of such heating. Perpendicular currents of the atmosphere are rarely seen, never extensive, or attaining any considerable altitude. I have watched for them thirty years. I have seen currents of air ascend, with their moisture condensing as they ascended, and unite with the under surface of a highly electrified cloud—the advance condensation of a thunder shower—but that cloud was moving horizontally at a distance of from one to two thousand feet above the surface of the earth, and did not rise. I have seen patches of scud rising from the surface during the intervals of a showery and highly electrified storm, toward, and uniting with, the clouds above, when very low, as I have seen them approach and unite horizontally; and doubtless there is a tendency upwards of the wind, created and attracted by the summer shower, as may be seen in the ascending dust before the rain, but I have never been able to detect an ascending current, except as induced and attracted by a cloud above moving horizontally, in the hottest day or dryest time. None of the clouds of our climate, even when the earth is heated and parched by a two months’ unbroken drought, can be detected rising above the strata in which they form. I have watched the cumuli at such periods when they filled the air, and can assert that they never rise. The atmosphere moves, invariably, in horizontal strata, and the whole theory of ascending currents is fallacious.

But let us look still further at the tropical currents. The true harmattan of north-western Africa (for the term is sometimes misapplied), hot and blistering, generated upon the sand of the desert—why does it blow from Sahara horizontally, on or over cooler surfaces, following the belt of rains as a N. E. trade? Why does it not ascend? The sirocco of north Sahara, the kamsin or chamsin of eastern Sahara, and the simoon of Arabia, which blow hot and suffocating from those deserts—why do they blow from heated surfaces and horizontally over cooler ones? Why do they not ascend? Arabia is surrounded on three sides by seas and gulfs, from which evaporation is rapid. Her interior deserts are extensive and intensely hot—why are they rainless? Why do they not have a vortex, a monsoon, or even a shower? Because there is no such law or action as this theory supposes. Those winds blow horizontally in obedience to other laws, and under the control of other and more powerful agents. But further still, what heating and ascending process is it that makes the variable winds north of the tropics? that brings in the warm air and fog of the Gulf Stream upon our snow-clad coast, in mid-winter, to increase the January thaw? Nay, what heating process is it that disturbs the calms of the polar regions with fresh breezes and gales, sometimes of the force of 6, when the sun does not shine, the thermometer is from 20° to 40° below zero, the earth and sea one frozen surface, and the hardy explorer dressed in furs, barely lives in his cabin covered by an embankment of snow, and heated by a stove?

Gentlemen, meteorologists, it will not do. The theory is unsound; the assumed facts do not exist. The whole universe has not an agent, organic or inorganic, which can play such absurd and inconsistent pranks in the face of its Creator, as your various and complicated theories assign to caloric.

Away with the theory and all its incidental and complicated and mystified hypotheses, they rest like a pall upon the science;—away with the whole system, and let us seek some agent whose power and adaptation correspond with the extent, and simplicity, and magnificence of the phenomena, and, in some degree, with the power and wisdom of their Author.

CHAPTER V.

One, and the principal end attained by the power of the agent, is the gathering of a volume of atmosphere from, or near, the surface of the land and sea, so as to ensure its possession of all the moisture of evaporation which rises from the locality, and the highest degree of temperature, and from a space ranging from one to two thousand miles in width, in one hemisphere, and to carry it over into the other. Not over the top, or upon the top, of the whole mass of atmosphere situated in the opposite hemisphere—out of reach of all influences from the earth—but through it, and curving gradually down near to, and within influential distance of the surface of the earth, soon after it passes the outward limit of its fellow trade; and to continue the current onward, leaving portions of it and its heat and moisture on the way, but taking a considerable volume up and around the magnetic poles—it being impossible for the entire volume to be thus carried around the poles in consequence of the diminished circumference of the earth. To this end it is obvious it must possess polarity.

Another end to be attained is to combine the moisture of evaporation with the air, so that the cold atmosphere through which, or the earth over which it passes, may not be continually condensing its moisture, and thereby enveloping the earth in a perpetual mist; but so that it may part with it at intervals, making cloudy and clear days; and part with it in portions, so that a regular and necessary supply may be furnished to the entire hemisphere, even up to the geographical poles. Is there such an agent? There is, precisely and perfectly adapted to the ends to be attained, ever there and ever active, and that agent is magnetism.

Fig. 12.

The earth is a magnet. It has its magnetic poles, and they are distinct from its geographical ones; and there are two in each hemisphere. They are situated from 17° to 19° distant from the geographical poles; and ours is not far from longitude 97° W. from Greenwich, and 71° north latitude. Navigators have gone north and north-west of it, and found its situation by the declination of the needle. From these poles, lines of magnetic intensity extend to the opposite and corresponding pole of the other hemisphere, and upon or near those lines the needle points north without variation; and toward these lines of no variation the needle every where, on either side declines. The foregoing diagram shows the situation of our magnetic pole and line of no variation, the dip of the needle by the arrows, and the magnetic equator.

Recent discoveries have shown that the magnetic force is exerted in lines and currents; that such currents, as physical lines of force, surround magnets, and currents of electricity. Doubtless such lines of force exist around the earth and the magnetic poles. There are also longitudinal lines of force existing and active, between the poles, and extending from one side of the center to the other, occupying nearly one third of the magnet. If you take a large needle thoroughly magnetized, place it upon paper and drop filings of iron upon it, they will become arranged about it in circular and perpendicular, and also in longitudinal lines, conforming to the currents.

Fig. 13.

This experiment is illustrated in all our books on natural philosophy.

The foregoing diagram, copied from Olmstead’s Philosophy, does not show as accurately as Faraday’s projection of the lines upon a globe-magnet the comparative distance from the poles of the needle, at which the longitudinal currents commence and terminate, and where the filings will not adhere to any considerable extent. The lines shown upon the needle should bear the same proportion to its length as the trade-winds bear to that of the earth, measured from pole to pole, and if the needle had a globular form they would so appear.

These lines are made by currents arising from one side of the magnetic equator, and passing over to the other. Doubtless, just such currents rise, and pass over upon the earth.

Magnetic and electric currents carry the air with them. This is well settled by experiment. Oxygen, too, is magnetic, and capable both of receiving and retaining polarity and of combining with, or attracting and retaining vapor, and of course the moisture of evaporation. Here then we have a power existing, capable of producing the result—precisely, and with evident wisdom adapted to its production—ever present and active; and no other known agent can.

Is it not then the agent?

Let us look a little further. This result is affected by the action of the sun: the trades with the central belts of rains travel north and south after it; so does the sun affect the magnetic currents every where, even the magnetic needle is daily affected by its action, as it increases the intensity of the terrestrial magnetic currents, and hence its well established diurnal oscillations.

Again, along the eastern lines of the continents which skirt the great oceans on the west, run the northerly and southerly lines of no variation, and of greatest magnetic intensity. Here are the trade currents gathered into a volume, which curve and carry unusual fertility to South-eastern Asia, and North America, and in those great aerial gulf streams we find the intense electric action which produces the typhoons of the former, and the hurricanes of the latter. It may still be said that these conditions and phenomena of the trade-wind region, are not produced by magnetism or magneto-electricity, but the objector can point to no other adequate power. That it must be heat, electricity, or magnetism, must be admitted. There is no other power known. Heat demonstrably can not produce them. Magnetism or electricity therefore must, and they are doubtless states or phases of the same power, producing in their different states or phases the different results. And even heat—atmospheric temperature, is often, if not always the result of their action. In the present state of science, it is enough for me that the magnetic longitudinal currents are there; that they are lines of force and adequate; that oxygen is magnetic, and therefore the atmosphere must be affected by them—that so far as we can reason from analogy, they ought to produce the effect upon the atmosphere which we find produced, and until further light is thrown upon the subject I shall presume that they do. Every step we take hereafter in this investigation will confirm the presumption.

There is one peculiarity to be more particularly noticed before we leave the trade-wind region, and we are now prepared to notice it.

The belt of rains, formed by the currents of the two trades, threading their way through each other—how are they produced? Why should the place where the currents thus pass through each other be a place of almost daily precipitation? There is, in fact, no ascension, except that which the currents have in their line of ascent to attain the elevation which the magnetic law of the current requires.

The trades have passed over an evaporating surface and are charged with moisture. This moisture they hold in magneto-electric combination. Evaporation does not depend upon temperature. Ice and snow evaporate at all temperatures (Howard, vol. 1, p. 86). So the cold N. W. wind, full of positive electricity, will lap up, as it were, the pools from the earth, with astonishing quickness; and when this electricity is deranging the action of the machinery and material of the manufacturer, he allays it by a supply of moisture, with which the electricity can combine. Nor does the air lose its moisture when below the freezing point. In all parts of the atmosphere, as at the surface of the earth in winter, moisture is held in large quantities in the coldest and severest weather; and it is not till it moderates, and a perceptible electric change takes place, that it is precipitated as rain or snow. Doubtless there is an exposure of considerable surfaces, of opposite currents, charged with opposite polarity, and a constant depolarization where their surfaces meet. May there not be a consequent dissolution of the electro-magnetic combination between the air and moisture, or the excitation of that electric action which attends or produces like rains every where? and hence the constant precipitation. This is rendered probable, by the fact that precipitation, at the meeting of the trades, takes place in level countries in the day-time, between 10 A. M. and sunset, in showers, with thunder and lightning, as with us in summer, although among the mountains the rain sometimes falls in the night also. The precipitation in the heat of the day is obviously induced by the action of the sun, although it is by no means certain that the friction of the opposing surfaces does not assist in the operation.

I am well aware that the lines of magnetic force curve upward and carry the trades with them, and that, therefore, precipitation by condensation from the mere cold of the upper stratum of the atmosphere is possible. But, there are three reasons why I do not believe such to be the fact.

1st. Precipitation takes place in the day time mainly, and in sudden, isolated, heavy showers and not in steady continuous rain. Nor is there condensation or continual mist at other hours of the day.

2d. They occur at a time of day when the sun is affecting the magnetic currents most powerfully, viz., between ten o’clock A. M. and sunset, and mainly at the time of greatest heat.

3d. The counter-trades do not precipitate after they leave the rainy belt, although at a great elevation, until they reach the outward limits of the trades; and they do precipitate again, although they gradually descend nearer the earth, as soon as they become subject to the action of the currents of an opposite magnetism. Their precipitation is partial too, even then, and they carry a portion of their moisture through an atmosphere of the coldest temperature up to the geographical poles.

A similar result attends the action of the sun in the extra-tropical regions. Cumuli commence forming in the counter-trade, or at the line between that and the surface current, at the same time of day that the diurnal motion of the magnetic needle commences, or the rain clouds form in the tropics; they continue to enlarge here as there, till about the same hour of the day that the needle obtains its maximum diurnal variations; and when the influence of the sun upon the needle ceases, and it returns to its original status, the cumuli disappear. Hail storms too, it is said, always, or generally occur in the day time.

In like manner the sea-breezes and other fair-weather surface winds, rise in the forenoon with the influence of the sun upon the magnetic currents and the needle, and die away at nightfall when the influence ceases.

There are other electro-magnetic, or to speak more correctly, magneto-electric, effects of the sun’s action equally illustrative, which tend to show that the precipitation at the passing of the trades, is the result of their action upon each other, aided by the sun, to which we shall allude when we come to speak of the causes and character of the surface winds of the extra-tropical regions.

As, however, this takes place only, or mainly, where the threading surfaces meet, it is but partial, and the body of the respective polarized currents pursue their way unaffected, toward the opposite magnetic pole—and there for the present we leave them.