constant winds. If the earth stood still, no doubt the direction would
be due north and due south for these winds; but the earth rotates
rapidly from west to east upon its axis, carrying with it everything
that is securely fastened to the surface: the trees, the houses, etc.
But the air is not a part of the earth, not even so much as the seas,
the waters of which must stay in their proper basins, and be whirled
around with other fixed objects. The earth whirls so rapidly that the
winds from north and south of the Equator lag behind, and thus take a
constantly diagonal direction. Instead of due south the northern belt of
cold air drifts south-west and the southern belt drifts northwest. These
are called the Trade Winds. Near the Equator they are practically east
winds.
The belt of trade winds is about fifty degrees wide. It swings northward
in our summer and southward in our winter, its centre following the
vertical position of the sun. Near the centre of the course which marks
the meeting of the northern with the southern winds is a "Belt of
Calms" where the air draws upward in a strong draught. The colder air of
the trade winds is pushing up the columns of light, heated air. This
strip is known by sailors as "the Doldrums," or "the region of
equatorial calms." Though never wider than two or three hundred miles,
this is a region dreaded by captains of sailing-vessels, for they often
lie becalmed for weeks in an effort to reach the friendly trade winds
that help them to their desired ports. Vessels becalmed are at the mercy
of sudden tempests which come suddenly like thunder-storms, and
sometimes do great damage to vessels because they take the sailors
unawares and allow no time to shorten sail.
Until late years the routes of vessels were charted so that sailors
could take advantage of the trade winds in their long voyages. It was
necessary in the days of sailing-vessels for the captain to understand
the movements of winds which furnished the motive power that carried his
vessel. Fortunate it was for him that there were steady winds in the
temperate zones that he could take advantage of in latitudes north of
the Tropic of Cancer and south of the Tropic of Capricorn. What becomes
of the hot air that rises in a constant stream above the "Doldrums,"
pushed up by the cooler trade winds that blow in from north and south?
Naturally this air cannot ascend very high, for it soon reaches an
altitude in which its heat is rapidly lost, and it would sink if it
were not constantly being pushed by the rising column of warm air under
it. So it turns and flows north and south at a level above the trade
winds. Not far north of the Tropic of Cancer it sinks to the level of
sea and land, and forms a belt of winds that blows ships in a
northeasterly direction. Between trades and anti-trades is another zone
of calms,--near the Tropics of Cancer and of Capricorn.
The land masses of the continents with their high mountain ranges
interfere with these winds, especially in the northern hemisphere, but
in the Southern Pacific and on the opposite side of the globe the
"Roaring Forties," as these prevailing westerly winds are known by the
sailors, have an almost unbroken waste of seas over which they blow. In
the long voyages between England and Australia, and in the Indian trade,
the ships of England set their sails to catch the roaring forties both
going and coming. They accomplish this by sailing past the Cape of Good
Hope on the outward voyage and coming home by way of Cape Horn, thus
circling the globe with every trip. In the North Atlantic, traffic is
now mostly carried on in vessels driven by engines, not by sails. Yet
the westerly winds that blow from the West Indies diagonally across the
Atlantic are still useful to all sailing craft that are making for
British ports.
From the north and from the south cold air flows down into the regions
of warmer climate. These polar winds are not so important to sea
commerce, but they do a great work in tempering the heat in the
equatorial regions. We cannot know how much our summers are tempered by
the cool breath of winds that blow over polar ice-fields. And the cold
regions of the earth, in their brief summer, enjoy the benefits of the
warm breezes that flow north and south from the heated equatorial
regions.
The land, north and south, is made habitable by the clouds. They gather
their burdens of vapour from the warm seas, the wind drifts them north
and south, where they let it fall in rains that make and keep the earth
green and beautiful. From the clouds the earth gathers, like a great
sponge, the water that stores the springs and feeds rivers and lakes.
How necessary are the winds that transport the cloud masses!
The air is the breath of life to all living things on our planet. Mars
is one of the sun's family so provided. Plants or animals could probably
live on the planet Mars. Do we think often enough of this invisible,
life-giving element upon which we depend so constantly?
The open air which the wind purifies by keeping it in motion is the best
place in which to work, to play, and to sleep, when work and play are
done and we rest until another day comes. Indoors we need all the air we
can coax to come in through windows and doors. Fresh air purifies air
that is stale and unwholesome from being shut up. Nobody is afraid,
nowadays, to breathe night air! What a foolish notion it was that led
people to close their bedroom windows at night. Clean air, in plenty,
day and night, we need. Air and sunshine are the two best gifts of God.
THE WORK OF THE WIND
When the March wind comes blustering down the street, rudely dashing a
cloud of dust in our faces, we are uncomfortable and out of patience. We
duck our heads and cover our faces, but even then we are likely to get a
cinder in one eye, to swallow germs by the dozens, and to get a gray
coating of plain, harmless dust. We welcome the rain that lays the dust,
or its feeble imitation, the water sprinkler, that brings us temporary
relief.
On the quietest day, even after a thorough sweeping and dusting of the
library, you are able to write your name plainly on the film of dust
that lies on the polished table. Take a book from the open shelves, and
blow into the trough of its top. This is always dusty. Where does the
dust come from? This is the house-keeper's riddle.
The answer is not a hard one. I look out of my window on a street which
is famous as the road Washington took on his retreat from White Plains
to Trenton. It has always been the main thoroughfare between New York
and Philadelphia, and now is the route that automobiles follow. A
constant procession of vehicles passes my house, and to-day each one
approaches in a cloud of dust. The air is gray with suspended particles
of dirt. The wind carries the successive clouds, and they roll up
against the houses like breakers on the beach. Windows and doors are
loose enough to let dust sift in. When a door opens, the cloud enters
and lights on rugs and carpets and curtains. Any ledge collects its
share of dust. The beating of carpets and rugs disturbs the accumulated
dust of many months.
[Illustration: In this lonely Arizona desert the wind drifts the sand
into dunes, just as it does on the toe of Cape Cod]
[Illustration: The Grand Canyon of the Colorado shows on a magnificent
scale the work of water in cutting away rock walls]
The wind sweeps the ploughed field, and takes all the dust it can carry.
It blows the finest top soil from our gardens into the street. It blows
soil from other fields and gardens into ours, so the level of our land
is not noticeably lowered. The wind strips the high land and drops its
burden on lower levels. This is one of the big jobs the water has to do,
and the wind is a valuable helper. To tear down the mountains and fill
in the valleys is the great work of the two partners, wind and water.
Dead, still air holds the finest dust, without letting it fall. The
buoyancy of the particles overcomes their weight. We see them in a
sunbeam, like shining points of precious metal, and watch them. A light
breeze picks up bits of soil and litter, from the smallest up to a
certain size and weight. If the velocity of the wind increases, its
carrying power increases. It is able to carry bits that are larger and
heavier. The following table is exact and interesting:
_Velocity_ _Pressure_
_in Miles_ _in Pounds_
_per Hour_ _per Sq. Ft._
Light breeze 14 1
Strong breeze 42 9
Strong gale 70 25
Hurricane 84 36
The terrible paths of hurricanes are seen in forest countries. The trees
are uprooted, as if a great roller had crushed them, throwing the tops
all in one direction, and leaving the roots uncovered, and a sunken
pocket where each tree stood. On a steep, rocky slope, the uprooting of
scattered trees often loosens tons of rock, and sends the mass
thundering down the mountain-side. Much more destruction may be
accomplished by one brief tornado than by years of wear by ordinary
breezes.
The wind does much to help the waves in their patient beating on rocky
shores. If the wind blows from the ocean and the tide is landward, the
two forces combine, and the loose rocks are thrown against the solid
beach with astonishing force. Even the gravel and the sharp sand are
tools of great usefulness to the waves in grinding down the resisting
shore. Up and back they are swept by the water, and going and coming
they have their chance to scratch or strike a blow. Boulders on the
beach become pockmarked by the constant sand-blast that plays upon them.
The lower windows of exposed seaside houses are dimmed by the sand that
picks away the smooth surface outside, making it ground glass by the
same process used in the factory. Lighthouses have this difficulty in
keeping their windows clear. The "lantern" itself is sometimes reached
by the sand grains. That is the cupola in which burns the great light
that warns vessels away from the rocks and tells the captain where he
is.
In the Far Western States the telegraph poles and fence posts are soon
cut off at the ground by the flinty knives the wind carries. These are
the grains of sand that are blown along just above the ground. The trees
are killed by having their bark girdled in this way. The sand-storms
which in the orange and lemon region of California are called "Santa
Anas" sometimes last two or three days, and damage the trees by piercing
the tender bark with the needle-pointed sand.
Wind-driven soil, gathered from the sides of bare hills and mountains,
fills many valleys of China with a fine, hard-packed material called
"loess." In some places it is hundreds of feet deep. The people dig into
the side of a hill of this loess and carry out the diggings, making
themselves homes, of many rooms, with windows, doors, and solid walls
and floors, all in one solid piece, like the chambered house a mole
makes underground in the middle of a field. So compact is the loess that
there is no danger of a cave-in.
The hills of sand piled up on the southern shore of Lake Michigan, and
at Provincetown, at the toe of Cape Cod, are the work of the wind. On
almost any sandy shore these "dunes" are common. The long slope is
toward the beach that furnishes the sand. The wind does the building. Up
the slope it climbs, then drops its burden, which slides to the bottom
of an abrupt landward steep. There is a gradual movement inland if the
strongest winds come from the water. The shifting of the dunes threatens
to cover fertile land near them. In the desert regions, the border-land
is always in danger of being taken back again, even though it has been
reclaimed from the desert and cultivated for long years.
Besides tearing down, carrying away, and building up again the fragments
of the earth's crust, the wind does much that makes the earth a pleasant
planet to live on. It drives the clouds over the land, bringing rains
and snows and scattering them where they will bless the thirsty ground
and feed the springs and brooks and rivers. It scatters the seeds of
plants, and thus plants forests and prairies and lovely mountain slopes,
making the wonderful wild gardens that men find when they first enter
and explore a new region. The trade winds blow the warm air of the
Tropics north and south, making the climate of the northern countries
milder than it would otherwise be. Sea winds blow coolness over the land
in summer, and cool lake breezes temper the inland regions. From the
snow-capped mountains come the winds that refresh the hot, tired worker
in the valleys.
Everywhere the wind blows, the life-giving oxygen is carried. This is
what we mean when we speak of fresh air. Stagnant air is as unwholesome
as stagnant water. Constant moving purifies both. So we must give the
wind credit for some of the greatest blessings that come into our lives.
Light and warmth come from the sun. Pure water and pure air are gifts
the bountiful earth provides. Without them there would be no life on the
earth.
RAIN IN SUMMER
How beautiful is the rain!
After the dust and heat,
In the broad and fiery street,
In the narrow lane,
How beautiful is the rain!
How it clatters along roofs,
Like the tramp of hoofs!
How it gushes and struggles out
From the throat of the overflowing spout!
Across the window-pane
It pours and pours;
And swift and wide,
With a muddy tide,
Like a river down the gutter roars
The rain, the welcome rain!
The sick man from his chamber looks
At the twisted brooks;
He can feel the cool
Breath of each little pool;
His fevered brain
Grows calm again,
And he breathes a blessing on the rain.
--HENRY W. LONGFELLOW.
WHAT BECOMES OF THE RAIN?
The clouds that sail overhead are made of watery vapour. Sometimes they
look like great masses of cotton-wool against the intense blue of the
sky. Sometimes they are set like fleecy plumes high above the earth.
Sometimes they hang like a sullen blanket of gray smoke, so low they
almost touch the roofs of the houses. Indeed, they often rest on the
ground and then we walk through a dense fog.
In their various forms, clouds are like wet sponges, and when they are
wrung dry they disappear--all their moisture falls upon the earth. When
the air is warm, the water comes in the form of rain. If it is cold, the
drops are frozen into hail, sleet, or snow.
All of the water in the oceans, in the lakes and rivers, great and
small, all over the earth, comes from one source, the clouds. In the
course of a year enough rain and snow fall to cover the entire surface
of the globe to a depth of forty inches. This quantity of water amounts
to 34,480 barrels on every acre. What becomes of it all?
We can easily understand that all the seas and the other bodies of water
would simply add forty inches to their depth, and many would become
larger, because the water would creep up on their gradually sloping
shores. We have to account for the rain and the snow that fall upon the
dry land and disappear.
Go out after a drenching rainstorm and look for the answer to this
question. The gullies along the street are full of muddy, running water.
There are pools of standing water on level places, but on every slope
the water is hurrying away. The ground is so sticky that wagons on
country roads may mire to the hubs in the pasty earth. There is no use
in trying to work in the garden or to mow the lawn. The sod is soft as a
cushion, and the garden soil is water-soaked below the depth of a
spading-fork.
The sun comes out, warm and bright, and the flagstones of the sidewalk
soon begin to steam like the wooden planks of the board walk. The sun is
changing the surface water into steam which rises into the sky to form a
part of another bank of clouds. The earth has soaked up quantities of
the water that fell. If we followed the racing currents in the gullies
we should find them pouring into sewer mains at various points, and from
these underground pipes the water is conducted to some outlet like a
river. All of the streams are swollen by the hundreds of brooks and
rivulets that are carrying the surface water to the lowest level.
[Illustration: Rain and wind are the sculptors that have carved these
strange castles out of a rocky table]
[Illustration: All the water in the seas, lakes, rivers, and springs
came out of the clouds]
So we can see some of the rainfall going back to the sky, some running
off through rivulets to the sea, and some soaking into the ground. It
will be interesting to follow this last portion as it gradually settles
into the earth. The soil will hold a certain quantity, for it is made up
of fine particles, all separated by air spaces, and it acts like a
sponge. In seasons of drought and great heat the sun will draw this soil
water back to the surface, by forming cracks in the earth, and fine,
hair-like tubes, through which the vapour may easily rise. The gardener
has to rake the surface of the beds frequently to stop up these channels
by which the sun is stealing the precious moisture.
The water that the surface soil cannot absorb sinks lower and lower into
the ground. It finds no trouble to settle through layers of sand, for
the particles do not fit closely together. It may come to a bed of clay
which is far closer. Here progress is retarded. The water may
accumulate, but finally it will get through, if the clay is not too
closely packed. Again it may sink rapidly through thick beds of gravel
or sand. Reaching another bed of clay which is stiffer by reason of the
weight of the earth above it, the water may find that it cannot soak
through. The only way to pass this clay barrier is to fill the basin,
and to trickle over the edge, unless a place is found in the bottom
where some looser substance offers a passage. Let us suppose that a
concave clay basin of considerable depth is filled with water-soaked
sand. At the very lowest point on the edge of this basin a stream will
slowly trickle out, and will continue to flow, as long as water from
above keeps the bowl full.
It is not uncommon to find on hillsides, in many regions, little brooks
whose beginnings are traceable to springs that gush out of the ground.
The spring fills a little basin, the overflow of which is the brook. If
the source of this spring could be traced underground, we might easily
follow it along some loose rock formation until we come to a clay basin
like the one described above. We might have to go down quite a distance
and then up again to reach the level of this supply, but the level of
the water at the mouth of the spring can never be higher than the level
of the water in the underground supply basin.
Often in hot summers springs "go dry." The level of water in the supply
basin has fallen below the level of the spring. We must wait until
rainfall has added to the depth of water in the basin before we can
expect any flow into the pool which marks the place where the brook
begins.
Suppose we had no beds of clay, but only sand and gravel under the
surface soil. We should then expect the water to sink through this loose
material without hindrance, and, finding its way out of the ground, to
flow directly into the various branches of the main river system of our
region. After a long rain we should have the streams flooded for a few
days, then dry weather and the streams all low, many of them entirely
dry until the next rainstorm.
Instead of this, the soil to a great depth is stored with water which
cannot get away, except by the slow process by which the springs draw
it off. This explains the steady flow of rivers. What should we do for
wells if it were not for the water basins that lie below the surface? A
shallow well may go dry. Its owner digs deeper, and strikes a lower
"vein" of water that gives a more generous supply. In the regions of the
country where the drift soil, left by the great ice-sheet, lies deepest,
the glacial boulder clay is very far down. The surface water, settling
from one level to another, finally reaches the bottom of the drift.
Wells have to be deep that reach this water bed.
The water follows the slope of this bed and is drained into the ocean,
sometimes by subterranean channels, because the bed of the nearest river
is on a much higher level. So we must not think that the springs contain
only the water that feeds the rivers. They contain more.
The layers of clay at different levels, from the surface down to the
bottom of the drift, form water basins and make it possible for people
to obtain a water supply without the expense of digging deep wells. The
clayey subsoil, only a few feet below the surface, checks the downward
course of the water, so that the sun can gradually draw it back, and
keep a supply where plant roots can get it. The vapour rising keeps the
air humid, and furnishes the dew that keeps all plant life comfortable
and happy even through the hot summer months.
Under the drift lie layers of stratified rock, and under these are the
granites and other fire-formed rocks, the beginning of those rock masses
which form the solid bulk of the globe. We know little about the core of
the earth, but the granites that are exposed in mountain ridges are
found to have a great capacity for absorbing water, so it is not
unlikely that much surface water soaks into the rock foundations and is
never drained away into the sea.
The water in our wells is often hard. It becomes so by passing through
strata of soil and rock made, in part, at least, of limestone, which is
readily dissolved by water which contains some acid. Soil water absorbs
acids from the decaying vegetation,--the dead leaves and roots of
plants. Rain water is soft, and so is the water in ponds that have muddy
basins, destitute of lime. Water in the springs and wells of the
Mid-Western States is "hard" because it percolates through limestone
material. In many parts of this country the well water is "soft,"
because of the scarcity of limestone in the soil.
I have seen springs around which the plants and the pebbles were coated
with an incrustation of lime. "Petrified moss" is the name given to the
plants thus turned to stone. The reason for this deposit is clear.
Underground water is often subjected to great pressure, and at this time
it is able to dissolve much more of any mineral substance than under
ordinary conditions. When the pressure is released, the water is unable
to hold in solution the quantity of mineral it contains; therefore, as
it flows out through the mouth of the spring, the burden of mineral is
laid down. The plants coated with the lime gradually decay, but their
forms are preserved.
There are springs the water of which comes out burdened with iron, which
is deposited as a yellowish or red mineral on objects over which it
flows. Ponds fed by these springs accumulate deposits of the mineral in
the muddy bottoms. Some of the most valuable deposits of iron ore have
accumulated in bogs fed by iron-impregnated spring water. In a similar
way lime deposits called marl or chalk are made.
THE SOIL IN FIELDS AND GARDENS
City and country teachers are expected to teach classes about the
formation and cultivation of soil. It is surprising how much of the
needed materials can be brought in by the children, even in the cities.
The beginning is a flowering plant growing in a pot. A window box is a
small garden. A garden plot is a miniature farm.
_Materials to collect for study indoors._ A few pieces of different
kinds of rock: Granite, sandstone, slate; gravelly fragments of each,
and finer sand. Pebbles from brooks and seashore. Samples of clays of
different colors, and sands. Samples of sandy and clay soils, black pond
muck, peat and coal. Rock fossils. A box of moist earth with earthworms
in it. _Keep it moist._ A piece of sod, and a red clover plant with the
soil clinging to its roots.
_What is soil?_ It is the surface layer of the earth's crust, sometimes
too shallow on the rocks to plough, sometimes much deeper. Under deep
soil lies the "subsoil," usually hard and rarely ploughed.
_What is soil made of?_ Ground rock materials and decayed remains of
animal and plant life. By slow decay the soil becomes rich food for the
growing of new plants. Wild land grows up to weeds and finally to
forests. The soil in fields and gardens is cultivated to make it
fertile. Plants take fertility from the soil. To maintain the same
richness, plant food must be put back into the soil. This is done by
deep tillage, and by mixing in with the soil manures, green crops, like
clover, and commercial fertilizers.
_Plants must be made comfortable, and must be fed._ Few plants are
comfortable in sand. It gets hot, it lets water through, and it shifts
in wind and is a poor anchor for roots. Clay is so stiff that water
cannot easily permeate it; roots have the same trouble to penetrate it
and get at the food it is rich in. Air cannot get in.