Between the parallels of 35 deg. north latitude, and 35 deg. 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 deg. south in the
Atlantic, to 10 deg. 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 deg. 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 deg., 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 deg.
north latitude, as in some places in summer when the sun is at the tropic
of Cancer; or whether at 20 deg. to 30 deg. 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.
[Illustration: Fig. 10. IN SUMMER.]
[Illustration: 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 deg. at least of the 180 deg. 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 Killingiae, 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 deg. and 30 deg. 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 deg., 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 deg. 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 deg. to 160 deg. of Fahrenheit. Under the
central belt of rains neither the earth nor air exceed the temperature of
84 deg.. 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 deg. 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 deg. south, and down to 9 deg. or more
south, is 82 deg.. 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 deg. 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 deg. north
latitude, with the water at 75 deg. and air at 76 deg., trade-wind N. E.
At 12 deg. 16' the water was 75 deg. the air 76 deg. wind N. E.
Feb. 22d. 9 deg. 49' " 76-1/2 deg. " 77 deg. " N. E.
" 23d. 7 deg. 13' " 78 deg. " 78 deg. " N. E.
" 24th. no obs. " 79-1/2 deg. " 79 deg. " N. E.,
E. S. E. rain.
" 25th. 3 deg. 10' " 81 deg. " 83 deg. " E. S. E. rain.
" 26th. no obs. " 82 deg. " 82 deg. " S. E. to
E. S. E. hazy,
rain & sqs.
" 27th. 2 deg. 24' " 82 deg. " 82 deg. " calm,
with rain.
" 28th. no obs. " 82 deg. " 82 deg. " calm rain.
March 1st. 0 deg. 29' " 82 deg. " 82 deg. " E. S. E.
sqs. rain.
" 2d. 1 deg. 27' S. L. " 82 deg. " 82 deg. " S. E. sqs.
rain.
" 3d. 2 deg. 44' " 82 deg. " 83 deg. " S. E. &
S. S. E.
weather
settled.
" 4th. 4 deg. 17' " 82 deg. " 83 deg. " S. S. E. &
S. E. fair
weather.
" 5th. 6 deg. 08' " 82 deg. " 84 deg. " S. E. fair
wthr.
" 6th. 8 deg. 08' " 82 deg. " 84 deg. " 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 deg., 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 deg., _and the
air rose to 83 deg. and 84 deg._! _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 deg. 22', longitude 71 deg. 26' as indicated by the
temperature of the water, which was as follows:
8 A.M. water at surface 66 deg.
9 " " " 73 deg.
10 " " " 76 deg.
11 " " " 77 deg.
77 deg. was the highest temperature found in crossing at this time.
Re-crossing it in May, in latitude 35 deg. 30', longitude 72 deg. 35', he
found the water as follows:
8 A.M. water at surface 71 deg. 8'
9 " " " 73 deg.
10 " " " 75 deg. 5'
11 " " " 78 deg. 5'
12 M. " " 78 deg. 5'
79 deg. 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 deg. to 40 deg. 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_.