OF WIND AND WATER
“He commandeth and raiseth the stormy wind, which lifteth up the waves
thereof.”--PSALM cvii. 20.
“Measure me a measure of wind.”--2 ESDRAS.
Over the great Deep of blue water lies the greater Deep of blue air.
And between these two--the Ocean of Air and the Ocean of Water, both
dragged earthward by the perpetual pull of gravitation--endless
intercourse takes place. Each finds its way in small fragments into the
other. There is always water present in the air. There is always air
present in the water.
Perhaps the latter fact is not so widely recognised as the former; yet
it is equally true. Sea-water contains large supplies of dissolved
gases, absorbed by the ocean-surface from the atmosphere, and passed on
into lower depths, for the use of creatures living there.
But the presence of water in air is known to us all. When we casually
remark, “What a damp day it is!” we mean, “What an amount of water
to-day is in the atmosphere!”
Water-vapour, drawn up from Ocean’s broad bosom, is carried far and
wide “on the wings of the wind,” to fall as rain where needed; and
drying winds in their turn pass over regions where much rain has
fallen, to bear away superfluous moisture.
A good deal was said in the last chapter about oceanic currents; and
mention was made of Winds as their chief cause.
That the power of wind over water is great, anybody may know who
has watched the lashing of the ocean into fury by a gale. But the
degree of that power was scarcely grasped, until within the last
few years. Rivers and streams in the sea were long ascribed to any
cause, except the most weighty of all. No one supposed _the_ immense
current-producing force to be that of Wind--not of mere local breezes
or gales here and there, but of strong constant winds, which prevail
month after month over wide ocean-districts.
When a storm-wind pours up a narrowing gulf, where the sea has no
outlet, it often piles the water up in an extraordinary manner.
Hurricanes have been known to turn the entire Gulf Stream for a while
out of its course, and even to force the waters back so as actually
to reverse the current. Once the volume of water, thus checked by a
terrific gale, was heaped up some thirty feet above the proper level,
which of course caused a fearful deluging of the land.
The above words had not been long written, when papers told us of the
awful hurricane of September, 1900, in U.S. Texas. A deep cyclone
passed over the devoted town of Galveston, the direction of the wind
suddenly changing as the centre of the cyclone went by: and the
heaped-up waters from either side coming together poured their united
volume over the land.
That was a flood which “turned the city into a raging sea.” Buildings
were levelled; houses fell like packs of cards; vessels were carried
miles inland; men and women and children perished by thousands. When
the lessening wind allowed the waters to retire, an inch-deep layer of
slime was found over everything.
Such facts as these help to show how vast is the power of moving air
over the ocean.
As a strong wind blows, the upper layer of water slips along in
obedience to its push; and fresh lower surfaces are bared to the same
influence. Also, the movement of the upper layer tends to drag on
the layer just below, which again affects the one lower still. By
influence thus exerted and passed from one to another, the result of a
long-continued wind-pressure in one direction is to set going powerful
streams, which in the first instance were due chiefly or only to wind.
Round the Earth, where fairly open sea permits them to develop, are
two wide belts of very persistent winds--the Trades--which remain
practically the same all the year round; only shifting their limits
with the changing seasons.
They blow from the north-east and from the south-east slanting towards
the equator. So, speaking roughly, they are easterly winds travelling
towards the west. As a consequence of their steady pressure, we have
the great Equatorial Current of the tropics, pouring from east to west
in two halves, north and south of the equator. This vast ocean-river,
started and kept going by the trade-winds, has been described in the
more important part of its course as a “magnificent surface-current of
hot water, four thousand miles long by four hundred and fifty broad,”
moving “at an average rate of thirty miles a day”--and, it may be
added, at least over six hundred feet in depth.
Between the Trade-wind belts is a belt of dead calms, known to sailors
as “The Doldrums.” This belt divides in two the Equatorial Current; and
in it is found the inevitable “Counter Current,” mentioned earlier,
flowing from west to east.
Another belt of steadfast winds is that of the “Roaring Forties,” in
the Southern Ocean; a wide stretch of all but landless sea, between
40° and 50° south latitude. These “Brave West Winds,” as they are
called, being again the reverse of the easterly Trades, blow all the
year round, and nearly all the world round, since only the southern
extremity of South America interferes with them.
They too give birth to a powerful current, flowing from west to east;
and this mighty stream, almost encircling the Earth, has a mission to
fulfil.
Already it has been said that each lesser ocean in the world has its
own separate circulation-system. This southern stream, with the Roaring
Forties for its parent, has for its especial task to unite all those
smaller systems into one. It has to refuse to the minor oceans a
lonely and self-absorbed policy, and to insist on the great truth of
a world-wide Ocean unity. It has to carry gifts from the Pacific to
the Atlantic, from the Atlantic to the Indian, from the Indian to the
Pacific again. It has to despatch streams northward into more distant
regions, with messages of goodwill to all.
Is this somewhat imaginative? Well, be it so. The facts are
scientifically true. Suggested meanings, gathered therefrom, may be
accepted or rejected, according to the reader’s pleasure.
We see, at all events, that from the vast Drift-Currents of the
Ocean, born of the Winds, spring the Grandchildren of the Winds,
such powerful rivers as the Gulf Stream and the Black Stream; they
in their turn giving birth to an infinite number of lesser currents,
Great-grandchildren of the Winds;--one and all taking their share in a
world-wide circulation of Ocean-waters.
The southern belt of westerly winds, with its resulting westerly
current, would be repeated in the northern hemisphere, but for the
presence of great masses of land. Continents work havoc with schemes of
ocean circulation.
That westerly winds do greatly prevail in corresponding latitudes to
the north is a well-known fact, though we cannot boast the possession
of anything like the “Roaring Forties.” No broad belts of unchanging
air-currents can exist in the neighbourhood of so much land, for the
counter-influences are too many.
From steadfast Wind-belts, giving birth to steadfast Ocean-streams, we
pass naturally to those fitful storms which lash the ocean into passing
passions, and to the uncertain breezes of temperate climes.
There are currents and counter-currents, breezes and contrary breezes,
winds from north and south and east and west, over the whole earth.
Each separate movement of air helps to stir the waters of the sea into
renewed restlessness.
Though few things are more wonderful than those vast rivers of air and
water, pouring always in the same direction, century after century,
they are perhaps less impressive from a man’s point of view than many a
mere whirling eddy, which flings itself along, rousing a huge flurry of
water, and soon dying out of existence. A man cannot grasp as a whole
the Trades or the Roaring Forties, with their companion ocean rivers.
Practically he knows only that little portion of each which happens to
be near his ship. If he is overtaken by a hurricane, the whole life of
which is compressed into a few miles of space and a few hours of time,
he feels a greater awe.
Small wonder that he should. Those impetuous and short-lived eddies
are terrible in their fury. Their winds blow with a fierceness never
approached by the stiffest Trade. A hurricane, tearing over Earth’s
surface at the rate of one hundred and twenty miles an hour, reduces
the most muscular of men to helplessness.
None the less, such a hurricane is in itself a mere accident, a mere
passing incident, a mere swirl of air, coming into being to adjust a
lost balance, and vanishing so soon as its work is done. We have seen
tiny swirls of air dancing along the road, on a windy day, sweeping up
bits of straw or dried leaves into their embrace. Such little swirls
are hurricanes in miniature. The real thing levels forests, wrecks
towns, lashes the ocean into mountainous heights of water, sinks
gallant ships, destroys human lives. Yet the little swirl and the
hurricane are closely akin.
Only in recent years has the circular--more strictly, the oval--shape
of a hurricane become known. It may be described as a revolving eddy
of air, the winds pouring in a corkscrew-like fashion round the
centre, inwards from without, and upwards from within. Another kind of
air-eddy, called an anti-cyclone, gyrates just the other way, downward
and outward. This usually brings light winds and dry weather, instead
of storms and rain.
One might imagine that in the centre of a wild cyclone a ship could
find safety, because there calm reigns. But the furious whirl of winds
all around raises tumultuous billows; and towards the centre, although
the winds themselves die down, the state of the sea is a perfect
“chaos” of tempestuous waves converging from all sides. Sailors strive
their utmost to avoid that central chaos.