The Philosophy of the Weather Part 7

The indications are those of condensation, and vary very much in different seasons of the year. It is not my purpose in this place to examine them particularly. They will be alluded to hereafter under the head of prognostics. Suffice it now to say, then, that whether it be the long threads or lines of cirrus which occur in the trade in the winter after a period of severe cold, following the interposition of a large volume of N.

W. cold air and the elevation of the counter-trade; or the forms of cirrus which occur at other times and other seasons; or whether it be the ordinary bank at night-fall, or the evening condensation which makes the "circle" around the moon, or the morning cirro-stratus haze which gradually thickens, pa.s.ses over and obscures the sun, all which may be followed by the easterly scud and winds: they are alike condensation in the trade, the advance or forming condensation of a storm or showers.

The state of the weather, whether hot or cold, is extensively affected by this trade current. As we have already suggested, the mere presence of the sun in its summer solstice, or its absence in winter, is not an adequate cause of all the sudden and various changes to which we are subject. The state of the counter-trade, which is always over, or _within influential distance of us_, and sometimes probably in contact with us--the nature of the surface-winds which it is at any given time creating and attracting around us, and the electric condition of the surface-atmosphere _induced_ by it, or by the immediate action of the earth's magnetism, produce those sudden changes which mark our climate. When no intervening surface-winds elevate it above us, and there is no storm or other condensation within influential distance, it induces the gentle balmy S. W. wind of spring--the cooling S. W. wind of summer--the peculiar Indian summer air of autumn, or the comparatively moderate, although cold, open weather of winter. If there be a partial tendency to condensation in it, the c.u.muli form under the magnetic influence excited by the sunbeams from ten to three o'clock in the day, and float gently away to the eastward, disappearing before night-fall. If the disposition to condensation is stronger, whether inherent or induced by an increased local activity of terrestrial magnetism, these c.u.muli will increase toward night-fall, or earlier, and terminate me showers; and if it is in a highly electrical state, the still oppressive sultriness which precedes the tornado, and that devastating scourge may appear. If this disposition to condensation becomes extensive, cirri form and run into cirro-stratus, or they extend, coalesce, and form stratus; the surface-wind will be attracted under them, the thermometer fall in summer or rise in winter, and a storm begin.

Intense action and sudden cold may exist in and under this counter-trade over the southern portion of the country, while all is calm, warm, and balmy at the north. Heavy snow storms sometimes pa.s.s at the south when there are none at the north, and a corresponding state of the weather follows. If a large body of snow fall at the north, the winter is cold, regular, and "old fashioned;" if little snow falls at the north and more at the south, the winter at the north is open and broken. I have known the ice make several inches thick at Baltimore and Washington, when none could be obtained for the ice-houses on the Connecticut sh.o.r.e of Long Island Sound. In short, although heat and cold are mainly dependent upon the alt.i.tude of the sun, aided by the other arrangements we have alluded to, yet the counter-trade, and the reciprocal action which takes place between it and the earth, are most powerful agents, mitigating the rigors of winter, bringing about the changes from cold to warm weather which the sun is too far south to produce. And on the other hand, by this reciprocal action, producing the electrical phenomena, the gusts, the tornadoes, the hail storms, and the cool seasons of summer, and the period of intense cold in winter.

_All our surface-winds, except the light, peculiar W. S. W. wind which is felt where the counter-trade is in contact with the earth, and which is a part of it, and perhaps the genuine N. W. wind which is very peculiar, are incidents of the trade, and are due to its conditions and attractions._ We have already said this was true of the easterly wind and scud of a storm--it is alike true of all. The storm winds east of the Alleghanies are usually, though not always, from the eastward. They are sometimes from the southward, as they doubtless are still more frequently in the interior of the continent.

There is occasionally a southerly afternoon wind, followed by short rains in spring and fall, or a succession of showers in summer, which is rather a precedent wind than a storm wind; blowing toward and under an advance portion of the storm at the north, and hauling to the eastward when the rain sets in, or to the westward when the showers reach us.

When there are no storms, or showers, or inducing electric action in the counter-trade, within influential distance to disturb the surface atmosphere, it is calm. If a storm approaches, or forms within inducing distance, the surface atmosphere is _affected_ and _attracted toward the storm_, from one or more points, and "blows," as we say, toward and under it. It commences blowing first nearest the storm, and extends as the storm travels, or becomes more intense and extends its inducing influence.

I have repeatedly noticed this in traveling on steamboats and railroads running _toward_ or _from_, and in several instances _through_ a storm, and telegraphic notices and other investigations prove it. The point from which the surface atmosphere is attracted and blows, depends very much upon the position of the storm in relation to bodies of water and the point of observation, and its shape; and the force with which it may blow will depend much upon its intensity.

Let us take an instance or two by way of ill.u.s.tration of all these points; and as I have given instances of summer in the introduction, we will take those of winter. It is January of an "old fashioned winter;" the snow is about three feet deep in Canada, about one foot in Southern New York, and a few inches in Philadelphia, and so extends west to the Alleghanies at least. For several days the sky has been clear, the thermometer rising in the day-time, in the vicinity of New York to about 25 Fahrenheit, falling at night to about 6, with light airs from the N. W. during the middle and latter part of the day; the counter-trade and the barometer both running high; cold but pleasant, steady, winter weather. There is a warm south-east rain and thaw coming, as one or more such almost invariably occur in January. How coming? The sun is far south, and shines aslant, but through a pure and windless atmosphere; he has tried for several days to melt the snow from the roof; a few icicles are pendant from the eaves; but the body of the snow is still there. How can a thaw come? not from the sun, surely. No, indeed, not from the action of the sun directly, upon our country, nor from the Atlantic or the Gulf Stream which is off our coast.

But a portion of the current of counter-trade is coming, heated by his rays and the warm water in the South Atlantic, in an intense magneto-electric state, capable of inducing an electro-thermal change in the surface atmosphere which it approaches, and of being reciprocally acted upon by the north polar terrestrial magnetism. It is now over Northern Texas and Western Louisiana, it will be here day after tomorrow.

The day pa.s.ses as the day previous had pa.s.sed; the sleigh-bells jingle merrily in the evening; the moon shines clear all night; the storm is coming steadily on, but its influence has not reached us, and the morning and midday are like those which preceded it. As nightfall approaches, however, the thermometer does not fall as rapidly as on the day previous; the sun shines dimly and through lines of whitish cirrus cloud extending from the horizon at the west, appearing darker as the sun descends and shines more _horizontally_ through them--perhaps mainly in the N. W.--and which extend up and over toward the E. N. E. The air next the earth begins to feel raw; it is changing, not from warm to cold, but _electrically_ from positive to negative; and dampening, from a tendency to condensation by induction, as we shall see--the same condensation which in warm weather may be seen on flagging stones, and walls, and vessels containing cold water. The advance cirrus condensation of the storm is over us and affecting us; the earth too is affecting the adjacent atmosphere by action extended from beneath the storm. Still there is no wind, although sounds seem to be heard a little more distinctly from the east, and so ends the day. Evening comes, and the moon wades in a smooth bank of cirro-stratus haze, with a very large circle around her; the cirrus bands of haze have coalesced and formed a thin stratus. The storm is coming steadily on, its condensation is seen to be thicker as it approaches, it is now raining from one hundred to one hundred and fifty miles to the west, but we do not know it.

That it is about to storm all believe, for all are conscious of a change.

The candle if extinguished will not relight as readily, if at all, on being blown; there is a crackling almost too faint for snow in the fire; the sun did not set clear; the old rheumatic joints complain, and the venerable corns ache.

Morning comes, and the storm is on. The wind is blowing from the S. E., the scud are running rapidly from the same quarter to the N. W., the thermometer continues rising, and it rains. The storm has reached us and the thaw has commenced. Gradually, as the densest portion of the storm cloud reaches us, it darkens; the scud are nearer the earth, and run with more rapidity; the rain falls more heavily and continuously, and by the middle of the day a thick fog has enveloped the earth; the wind is dying away, and the trade itself, with its southern tendency to fog, has settled near us; the barometer has fallen, the thermometer is up to fifty degrees, the water is running down the hills, the snow is saturated with water and is disappearing under the influence of the fog, the rain, and the warm air. Evening comes; the south-east wind and the rain have ceased; the rain clouds have pa.s.sed off to the eastward; the fog has followed on and disappeared; there is a light trade air from the S. W.; the moon shines out, and a few patches of stratus, broken up into fragments and melting away, are following on in the trade: the storm is past.

Hark! to the tones of Boreas as he bursts forth from the N. W., and rushing, whistling, howling, dashes on between the trade and the earth, following the storm. Now the barometer rises rapidly, the thermometer falls, and in an incredibly short time all is congealed, and cold and wintery as before. The cold N. W. wind has again interposed between the trade and the earth; the trade is elevated a mile or more above it and is entirely free from its influence and from condensation; the deep blue of a sky "as pure as the spirit that made it" is over us, and steady winter reigns again.

It is obvious that there was nothing in the action of the sun upon our snow-clad country, to induce the thaw or the storm. It began, continued, approached, and pa.s.sed off to the N. E. in the counter-trade. The S. E.

wind which existed every where within its influence: in the interior States, Missouri, Illinois, Indiana, Ohio, Michigan, and in Canada, as well as upon the Atlantic coast, commencing in the former earlier than upon the last, was the result of its induction and attraction. Of the N.

W. wind that followed we shall speak hereafter. If any one doubts whether this be a true sketch let him examine the investigation of a storm published by Professor Loomis, or observe for himself hereafter. If, however, the storm of Professor Loomis is referred to, it should be remembered that his notes show the occurrence of a slight distinct snow storm at the N. W. stations one day in advance of the princ.i.p.al storm. The latter appears first as rain at Fort Towson, on the nineteenth, moving north and curving to the east--its center pa.s.sing near St. Louis, and south of Quebec, and the whole storm enlarging as it advanced.

Take another instance. Since the thaw it has not been quite as cold as before; but the rain-soaked snow is hard and solid, the ground, where the snow was blown or worn off, icy and slippery--the thermometer falls during the night to about 12, and rises to about 30; the sun makes no impression upon the snow; the firmament is of the deepest blue, the borealis at night vivid. "O, for a storm of some kind, to mitigate the still severe cold;" for the thaw has made us more sensitive, and storm winds do blow warm in their season. But patience, it will come. Another day, or two, perhaps, pa.s.s: the sun rises as usual, the thermometer has the same range still. "Long cold snap," we exclaim; "how long will it last?"

A change is coming, but this time it will snow. About an hour or two after sunrise the cirrus threads are discoverable again in the west, but now they are most numerous in the S. W. As the day pa.s.ses on they thicken and advance toward the E. N. E., the sun begins to be obscured, the thermometer rises, and it slowly "_moderates_." There is a snow storm approaching from the S. W.

But the thermometer rises slowly; it must get up to 26 or 28 before it can snow much. I have known in one instance, at Norwalk, a considerable fall of snow, although much mingled with hail, when the thermometer stood at 13 above zero, and one, a moderate fall, some two inches, with it at 24, but these were exceptions. The snow range of the thermometer on the parallel of 41 north lat.i.tude, and south of it, is from 26 to 30 above 0; when colder or warmer it may snow to whiten the ground, or perhaps barely cover it, but usually rains or hails. We have seen that in the polar regions, according to Dr. Kane, it is about zero, but the rise of the thermometer there, previous to the snow, was about the same as here, _i. e._, from 15 to 25. This fact is instructive. Since the foregoing was written, and on the 7th of February, 1855, a snow-storm of considerable length set in, with the thermometer at 5, and continued more than twenty-four hours, the thermometer gradually rising. The snow was very fine, like that described by Arctic voyagers as falling in extreme cold weather.

As the dense and darker portions of the storm approach, and although the sun is obscured, and the ground frozen, it continues to moderate, and at evening, when the thermometer is up to 28, and the dense portion of the storm has reached us, gently and in calmness the snow begins to fall.

Perhaps a light air following the storm, or the presence of the trade near the earth, at first inclines the snow-flakes to the eastward. This is frequently so at the commencement of snow storms. Ere long, however, the wind rises from the N. E., and the snow is driven against the windows, rounded and hardened by the attrition of its flakes upon each other, in their descent through the eddying and opposite currents. The next day we rise to witness a heavy fall of snow, perhaps, and a continued driving N.

E. storm, in full blast; the snow whirling and settling in drifts under the lee of every fence or building.

Can it be, you ask, that this driving wind is but an _incident_ of the storm? the result of _attraction_, while the storm clouds are sailing quietly and undisturbed on in the counter-trade above, directly over the gale which is blowing below? It is even so. Nor has it "backed up," as it is termed by those who have ascertained that it has commenced snowing first, and cleared off first, at a point west of them. You saw, or might have seen, the cirro-stratus cloud pa.s.sing to the E. N. E. in the afternoon, and until the snow-flakes filled the air, and the clouds became invisible. You may still see that the wind will die away before the storm breaks, and "come out" gently from the S. W., unless it should back into the northward and westward, and in either event you may see the last of the storm clouds, as you did see, or might have seen the first of them, pa.s.s to the eastward. Toward night the wind dies away, and the storm pa.s.ses off abruptly, or the sky becomes clear in the N. W. Now you may see the smooth stratus storm cloud, continuous, or breaking up into fragments and pa.s.sing off to the east, even at the edge which borders the clear sky in the west or north-west, to be followed that evening or the next day, by the north-west wind and its peculiar fair-weather scud.

I have given these as instances ill.u.s.trating the manner in which rain and snow storms originate the surface easterly winds in winter.

But it must not be supposed that they commence with precisely the same appearances in every case in winter; much less in summer. There is very great diversity in this respect, in different seasons, and in different storms during the same season. A great many different and accurate descriptions might be given, if time and s.p.a.ce would permit, which all would recognize as truthful. Very frequently in summer, and sometimes in winter, the wind will set in from the eastward, and blow fresh toward a storm, before the condensation in the trade, which forms the eastern and approaching edge of the storm, has a.s.sumed the form of a distinct cloud.

Not unfrequently, when it is calm next the surface, a narrow stratum of easterly wind, a half a mile or a mile above the earth, may be seen with a continuous fog, condensing, but not in considerable patches like the usual scud, running with great rapidity toward the storm. Such a stream of fog blew with great rapidity for thirty-six hours toward the storm which inundated Virginia and Pennsylvania, in 1852, and carried away the Potomac bridge at Washington. Such a stream of fog was visible the evening before the great flood of 1854, which inundated Connecticut, and curried away so many railroad and other bridges. I have also seen such a stream of fog running at about the same height, when it was calm at the surface, from the S. W. toward a violent storm which formed over central New England--and from the north toward a heavy storm pa.s.sing south of us. Such strata form, as far as I have been able to discover, the _middle current_ of storms which are accompanied with very heavy falls of rain. These double currents are much more common than is supposed. East of the Alleghanies, short and heavy rain storms, which commence north-east, hauling to the south and lighting up about mid-day _after a very rainy forenoon_, frequently have a S. E. or S. S. E. middle current of this character, which involves the whole surface atmosphere when the storm has nearly pa.s.sed, and the N. E. wind dies away, and the wind seems to haul to the S. S. E. and S.; so that it is rather the prevalence of a _different_ and _coexisting current_, than a hauling of the _same wind_, which marks the period of lighting up in the south.

Sometimes the easterly wind will set in and blow a day or two before the border of the storm reaches us. Sometimes the storm is pa.s.sing, or will pa.s.s, in its lateral southern extension, south of us, and the condensation in the trade extends over us sufficiently dense to induce an easterly current beneath it, but not dense enough to drop rain, and then we have a dry north-easter. I can not, within the limits I have prescribed, allude to all the peculiarities attending the induction and attraction of an easterly wind, by the storm in the counter-trade. They are readily noticeable by the attentive and discriminating observer, and their existence and cause is all with which I have to do at present.

Winds from the north, or any point from N. N. E. to N. N. W., are comparatively infrequent in the United States, east of the Alleghanies--though it is otherwise in the vicinity of the great lakes.

Sometimes the wind "backs," as sailors term it, during a N. E. storm, from the N. E. through the N. N. E., N., and N. N. W. to N. W. When this takes place, it is toward the close of the storm. Occasionally, though very rarely, it continues to storm after the wind has pa.s.sed the point of N. N.

E., and until it gets N. W. I have known a few instances in the course of thirty years, and but a few. They are exceptions--rare exceptions. When the wind thus backs from the N. E. to the N. W. through the N., you may be very certain that the body of the storm, or at least the point of greatest intensity and greatest attraction, is at the time pa.s.sing to the southward of you. This is most commonly the course of the wind when the storm extends far south and lasts several days, and does not extend north far, or if so, with much intensity, beyond the point of observation. The change of the wind is explained by the situation of the focus of intensity and attraction, to the south of the observer, and its pa.s.sage by on that side.

Probably in locations further north and (as I think I have observed) south of the lakes, it may be more frequent than upon the parallel of 44 east of the Alleghanies (which is as far north as I have observed), inasmuch as the further north the locality, the more likely storms and other disturbances in the counter-trade will be to pa.s.s to the southward of it.

Between the N. E. and S. E. the wind may blow from any point, before and during storms, and in a clear day in the morning, as a light variable breeze, or, after mid-day, toward approaching showers. I have known it blow all day during a storm from due east; to change back and forth between south-east and north-east, and to blow for hours from any intermediate point--as different portions of the storm were of different intensity, and exerted a more or less powerful inducing influence; and doubtless this often takes place at sea. It depends upon the situation of the focus of attraction of the storm, its shape relative to the particular locality, and with reference to the atmosphere east of it, and peculiar local magnetic action; or, as is sometimes the case in low lat.i.tudes, is owing to the fact that the storm is made up of many imperfectly connected showers, which have different force, and induce changeable and baffling winds.

The inducing and attracting influence of the approaching storm is exerted sooner, and with most force, upon the surface atmosphere, over bodies of water like the ocean and the lakes. Thus, the wind will set from the eastward toward an approaching storm out upon Long Island Sound, for hours before it is felt upon either sh.o.r.e; and when all is calm in the evening on land, and often before the moon forms a halo or circle in the milky condensation of the approaching storm, or any sign of condensation is visible, the breaking of the waves upon the sh.o.r.es may be heard. Doubtless this may be observed on the sh.o.r.es of the Atlantic at other points.

This power of attracting the surface atmosphere from bodies of water like the ocean and the great lakes, will account for two apparent anomalies, mentioned by Mr. Blodget in a valuable and instructive article read to the Scientific Convention, in 1853, regarding the annual fall of rain over the United States.

First--the influence of mountains in extracting the water from the atmospheric currents which pa.s.s over them, is well known and readily explainable. Mr. Blodget, however, found that the source of our rains, whatever it might be, when it reached the Alleghanies, was so far exhausted of its moisture that those mountains extracted less from it than fell to the westward, by some five to ten inches annually; and that the fall of rain upon them was less than upon the Atlantic slope eastward of them, to the ocean. This does not accord with observation elsewhere, but is easily explained. As the storm approaches the ocean, it attracts in under it the surface atmosphere of the ocean, loaded with vapor, condensing in the form of fog and scud, as it becomes subject to the increasing influence of the storm. Although the scud and fog would not of itself make rain, it aids materially in increasing the quant.i.ty of that which falls through it. The drops, by attraction and contact, enlarge themselves as they pa.s.s through, in the same manner as a drop of water will do in running down a pane of gla.s.s which is covered with moisture.

The small drop which starts from the upper portion of a fifteen-inch pane, will sometimes more than double its size before it reaches the bottom. _It is by this power of attracting the surface atmosphere, which contains the moisture of evaporation, under it, and inducing condensation in it, that the moisture of evaporation which rarely rises very far in the atmosphere is made to fall again during storms and showers._ This attraction of a moist atmosphere from the ocean accounts for the excess of rain on the east of the Alleghanies, compared with its fall upon them. So the great valley of the Mississippi is comparatively level, and less of its water runs off than of that which falls upon the Alleghanies. There is, therefore, more moisture of evaporation in the atmosphere of the former to be thus precipitated and add to the annual supply of rain upon that valley, and it exceeds that which falls upon the Alleghanies. Those mountains, too, are elevated but about 1,500 feet above the table-lands at their base, and exert little influence on the counter-trade. If they, were 6,000 or 8,000 feet high, a different state of things would exist.

Second--Mr. Blodget found the quant.i.ty of rain which fell in Iowa, and to the south and west of the lake region, to be greater than fell over the lake region itself. This is doubtless in part owing to the same cause. The counter-trade, in a stormy state, attracts the surface atmosphere from the lake region, with its evaporated moisture, before it arrives over it, and therefore more rain falls S. W. of the lake region than upon it. This power of attracting the surface wind of the ocean in under it, produces the heavy gales which affect our coast, and which are rarely felt west of the Alleghanies to any considerable degree; and a storm coming from the W.

S. W., extending a thousand miles or more from S. S. E. to N. N. W., may have the wind set in violently at S. E. on the _southern coast first_, and at later periods, successively, at points further north, and thus induce the belief that the storm traveled from south to north.

Mr. Redfield finding that some of the gales which he investigated, particularly that of September 3d, 1821, did not extend far inland, and commenced at later periods regularly, at more northern points, concluded that the gale traveled along the line of the coast to the northward. In this, and in relation to the storm of 1821 (and perhaps some others), he has been deceived. My recollections of that storm are accurate and distinct. But I shall recur to this again when I come to speak of his theory.

Toward storms, or belts of showers which would be storms if it were not summer and the tropical tendency to showers active in the trade, which pa.s.s mainly to the north of us, or commence north and pa.s.s over us, condensing south while progressing east, the wind may commence blowing before the body of the storm reaches us, from any point between south by west and south east, particularly in the summer season and in the afternoon. When the rain in a storm of this character sets in, in the night, it will sometimes haul into the S. E., if the focus of attraction be situated north of us, and so remain until just before the storm is to break.

There are, however, a cla.s.s of southerly summer winds which deserve more particular notice. For two or three months in the year--say from the middle of June to the 20th of August--storms on the eastern part of the continent, except in wet seasons, are rare, and most of our rain is derived from showers. During these periods belts of drought are frequent, sometimes in one locality, and sometimes in another, extending with considerable regularity from W. S. W. to E. N. E. in the course of the counter-trade, while rain falls in frequent and almost daily showers to the northward or southward of them. If the daily rains are at the north, over the belt of drought, S. S. W. and S. W. by S. winds blow, sometimes with c.u.muli or scud, during the middle of the day and afternoon, to underlie the showery counter-trade on the north of the line of drought.

Thus, sometimes nearly every day for several days, the evaporated moisture of the dry belt will be carried over to increase the store of those who have a sufficient supply without. During the latter part of the afternoon the clouds in the west may look very much like a gathering shower, but the attractions of the counter-trade fifty or one or two hundred miles to the north, will absorb them all, and at nightfall the wind will haul to the S.

W. on a line with the counter-trade, and die away.

If there be a drought on any given line of lat.i.tude, and frequent showers or heavy rains at the south of it, although there may not be a like surface-wind, with c.u.muli and fog, blowing from the north toward it, yet a general, gentle set of the atmosphere, from the N. N. W., or N. W., or other northerly point, toward the belt of rains, some distance above the earth, will often be observable, with a barometer continually depressed, and perhaps a cool atmosphere.

During set fair weather, when the attracting belt of rains is far north, on the north sh.o.r.e of Long Island Sound, the wind, like a sea breeze, will set in gently from about S. S. E. or S. by E. in the forenoon, blowing a gentle breeze through the day, and hauling to W. S. W. on a line with the trade at nightfall, and dying away. During a drought I have known this to happen for seventeen successive days. It is obvious to an attentive observer that this is the result of the influence of the sun in exciting the magnetic influence of the earth, and producing a state of the trade not unlike that which induces the formation of c.u.muli, and which attracts the surface atmosphere from the Sound in over the land: for the _tendency to c.u.mulus condensation precedes the breeze_, and the breeze is often wanting in the hottest days where no such tendency to the formation of c.u.muli exists. The same is true of sea breezes elsewhere. They do not blow in upon some of the hottest surfaces. Where they do exist, they do not always blow, but are wanting during the hottest days; and careful observers have identified their appearance with the formation of c.u.muli, or other condensation, upon the hills inland. They are not, therefore, the result of ascending currents of heated air.

The received theory regarding sea and land breezes is a mistaken one in another respect. There is no such thing as a land wind corresponding in force to, and the opposite of, the sea breeze--occasioned by the comparative warmth of the ocean. These breezes blow mainly within the trade-wind region. Of course they are either beneath the belt of rains or the adjoining trades. They are said to be, and doubtless are, most active and strongly marked on lines of coast, particularly the Malabar coast, and where the trade-winds are drawing usually from them. In the day-time, when the action of the sun increases the action of the magnetic currents upon the land, or there are _elevations inland_ which approach the counter-trade, and especially if it is elevated near the coast, as the Malabar coast is by the Ghauts, the attraction of this atmosphere over it _reverses the trade_, or inclines it in upon the land, and it blows in obliquely or perpendicularly, according to the relative trending of the coast and the direction of the surface-trade. Thus, where islands are situated within the range of the trades, the latter will be _reversed_ during the day on the _leeward_ side, but continue to blow as land winds during the night. So they are sometimes deflected in upon the land on the sides, during the day, and in like manner return to their course in the night. So, too, the north-east trades of Northern Africa, are occasionally (though feebly where the coast is flat) deflected during the day-time, and blow in as N. W. winds. Upon the southern coast of Africa the S. E. trade is deflected, and blows in as a S. W. wind. Upon the south-western coast of North America, the N. E. trades are deflected in like manner, and so are the S. E. trades upon the western coast of South America. Where the coast mountain ranges are very elevated, as upon the western coast of the American continent, this attracting influence and consequent deflection extends to a considerable distance seaward, and hence the westerly winds of California, etc. It must be understood that we are now speaking of the winds which blow within the range and during the existence of the trade-winds or the presence of the dry belt--for the trades are not always perceptible on the land. Captain Fitzroy thus describes the sea breezes of the western coast of Peru, at 23 south lat.i.tude. "The tops of the hills on the coast of Peru are frequently covered with heavy clouds. The prevailing winds are from S. S. E. to S. W., seldom stronger than a fresh breeze, and often very slight. _Sometimes during the summer, for three or four successive days, there is not a breath of wind, the sky is beautifully clear, with a nearly vertical sun._ On the days that a sea breeze sets in, it generally commences about ten in the morning, then light and variable, but gradually increasing till one or two in the afternoon. From that time a steady breeze prevails till near sunset, when it begins to die away, and soon after the sun is down there is a calm.

About eight or nine in the evening _light winds_ come off the land, and continue till sun-rise, when it again becomes calm until the sea breeze sets in as before."

To ill.u.s.trate this further, I take the following letter from Professor Espy's Philosophy of Storms:

CLINTON HOTEL, N. Y., Dec. 20, 1839.

TO PROFESSOR ESPY,

DEAR SIR,--Understanding you are desirous of collecting curious meteorological facts, I take the liberty of communicating to you what I saw in the month of December, 1815, at the Island of Owhyhee. I lay at that island in the Cavrico Bay,[3] in which Captain Cook was killed, three weeks, and every day during that time, very soon after the sea breeze set in, say about nine o'clock, a cloud began to form round the lofty conical mountain in that island, in the form of a ring, as the wooden horizon surrounds the terrestrial artificial globe, and it soon began to rain in torrents, and continued through the day. In the evening the sea breeze died away and the rain ceased, and the cloud soon disappeared, and it remained entirely clear till after the sea breeze set in next morning. The land breeze prevailed during the night, and was so cool as to render fires pleasant to the natives, which I observed they constantly kindled in the evening. I was particularly struck with the phenomena of the cloud surrounding the mountain, when none was ever seen in any other part of the sky, and none then till after the sea breeze set in, in the morning, which it did with wonderful regularity. The mountain stood in bold relief, and its top could always be seen from where the ship lay, above the cloud, even when it was the densest and blackest, with the lightning flashing and the thunder rolling, as it did every day. I pa.s.sed up through the cloud once, and I know, therefore, how violently it rains, especially at the lower side of the cloud. This rain never extends beyond the base of the mountain;[4] and all round the horizon there is eternally a cloudless sky. The dews, however, are very heavy, and there seems to be no suffering for want of rain. That this state of things continues all the year, I have no doubt, from what an American, by name Sears, who had spent four years there, told me; he had seen no change in regard to the rain.

CALEB WILLIAMS.

Providence, R. I.

Similar citations might be made to show that the sea breeze is induced by the same cause which forms the clouds over the land--that it is frequently wanting for three or four days under a vertical sun, and that the land breeze blows gently and not with corresponding force where there is no surface trade, or where it is deflected, not reversed.

A succession of showers pa.s.sing across the country to the north, within one hundred to one hundred and fifty miles, almost always produces a southerly wind to the southward of them. There is more that is peculiar about these belts of showers. Although they consist of large highly-electrified c.u.muli, there is a strong tendency to cirro-stratus condensation in the lower part of the trade over them; and it is that condensation rather than the c.u.muli, which attracts the surface atmosphere from the south. They would be storms, if the atmosphere had not a summer-tropical tendency to showers. There is, too, a tendency in these belts to extend to the south, and it is generally, as far as I have observed, the extension southerly of those belts, by the formation of new showers which terminate the "hot spells" or "heated terms" of mid-summer.

The very oppressive and fatal one of the summer of 1853, was, in character, a type of all--although exceeding them in severity. The first three or four days were calm, hot, and smoky--an appearance which attends all similar periods more or less, refracting the red ray of the light, and giving the sun a peculiar dry-weather, red appearance. (This smoky haze is usually atmospheric, and occasionally seen even in March, although not unfrequently fires in the woods fill the air with actual smoke, and very much increase it, and when this is so, the odor of the smoke is often perceptible.) Then we began to have a fresh south-west by south breeze in the day-time, hauling to the south-west, and dying away at nightfall. The next day, the tendency to condensation and consequent belt of showers having extended further south and approached nearer to us, the S. S. W.

wind blew _fresher_ toward it, and _did not die away at nightfall_. During the evening the reflection of the lightning playing upon the tops of the thunder clouds, just visible at the north (heat-lightning, it is termed, because supposed to be unaccompanied by thunder, but in reality lightning reflected from clouds at too great a distance for the thunder to be heard), and the continuance of the southerly wind after nightfall, gave sure evidence of the coming showers the next day, and an end of the excessive heat for that time. So ended both of those long-to-be-remembered "heated terms" of 1853.

The same is probably true of the interior of the country every where.