The Philosophy of the Weather Part 5

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 pa.s.sage 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, pa.s.sing 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 pa.s.s 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 lat.i.tude 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 a.s.sumed 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 a.s.sumes 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 lat.i.tude, 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 pa.s.s. 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 lat.i.tude 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 s.h.i.+pmaster, found in the wind and current charts of Lieutenant Maury, I abridge the following, which will ill.u.s.trate this. Captain Young in February, found the N. E. trades at about 17 north lat.i.tude, with the water at 75 and air at 76, trade-wind N. E.

At 12 16' the water was 75 the air 76 wind N. E.

Feb. 22d. 9 49' " 76-1/2 " 77 " N. E.

" 23d. 7 13' " 78 " 78 " N. E.

" 24th. no obs. " 79-1/2 " 79 " N. E., E. S. E. rain.

" 25th. 3 10' " 81 " 83 " E. S. E. rain.

" 26th. no obs. " 82 " 82 " S. E. to E. S. E. hazy, rain & sqs.

" 27th. 2 24' " 82 " 82 " calm, with rain.

" 28th. no obs. " 82 " 82 " calm rain.

March 1st. 0 29' " 82 " 82 " E. S. E.

sqs. rain.

" 2d. 1 27' S. L. " 82 " 82 " S. E. sqs.

rain.

" 3d. 2 44' " 82 " 83 " S. E. & S. S. E.

weather settled.

" 4th. 4 17' " 82 " 83 " S. S. E. & S. E. fair weather.

" 5th. 6 08' " 82 " 84 " S. E. fair wthr.

" 6th. 8 08' " 82 " 84 " S. E. & E. S. E. fair weather.

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 lat.i.tude 37 22', longitude 71 26' as indicated by the temperature of the water, which was as follows:

8 A.M. water at surface 66 9 " " " 73 10 " " " 76 11 " " " 77

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

Re-crossing it in May, in lat.i.tude 35 30', longitude 72 35', he found the water as follows:

8 A.M. water at surface 71 8'

9 " " " 73 10 " " " 75 5'

11 " " " 78 5'

12 M. " " 78 5'

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 a.s.sumed 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 alt.i.tude._ 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 c.u.muli at such periods when they filled the air, and can a.s.sert 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 s.h.i.+ne_, 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 a.s.sumed 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 a.s.sign 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 princ.i.p.al 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 s.p.a.ce 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 ma.s.s 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 pa.s.ses 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 circ.u.mference 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 pa.s.ses, 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_.

[Ill.u.s.tration: 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 lat.i.tude.

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.