Atlantic Monthly Vol. 6, No. 33, July, 1860 by Various

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Without light, however, there is no color. Agriculturists and chemists
understand this. Plants without light retain their oxygen, which
bleaches them.

The theory of color has never been fully agreed upon. Some writers
maintain that the character of its hues depends on the number of
undulations of a ray. Goethe's theory is substantially, that colors
are produced by the thinning or thickening and obstructing of light.
Brewster contends that there are but three primary colors,--red,
yellow, and blue. Wollaston finds four,--red, yellowish green, blue,
and violet. But this, as well as the consideration of the solar
spectrum of Newton, is more the specialty of Optics. The atmospheric
relations of color are more apposite to our purpose.

The color of the clouds, which may be occasionally affected by
electricity, is owing to the state of the atmosphere and its
reflecting and refracting properties.

The color of snow is white because it is composed of an infinite
variety of crystals, which reflect all the colors of light, absorbing
none, and these, uniting before they reach the eye, appear white,
which is the combination of all the colors.

Wind, the atmosphere in action, though not picturesque, is always
wonderful, often terrible and sublime. The origin of wind, its
direction and its force, its influence on the health of man, his
business, his dwelling-place, and the climate where he perpetuates his
race, have attracted the profound attention of the greatest
philosophers.

To the rarefaction of the air at the equator, and the daily revolution
of the earth, is attributed the origin of the Trade-Winds, which blow
from the east or a little to the north of east, north of the equator,
and east or south of east after we are south of the equator. The hot
current of ascending air is replaced by cold winds from the poles.

But why are we not constantly subject to the action of north winds,
which we rarely are? Because of the diurnal motion of the earth, which
at the equator equals one thousand miles an hour, the polar winds in
coming down to the equator do not have any such velocity, because
there is a less comparative diurnal speed in the higher latitudes. The
air at the poles revolves upon itself without moving forward;--at the
equator, the velocity, as we have mentioned, is enormous. If, then,
says Professor Schleiden, we imagine the air from the pole to be
carried to the equator, some time must elapse before it will acquire
the same velocity of motion from west to east which is always found
there. Therefore it would remain behind, the earth gliding, as it
were, from beneath it; or, in other words, it would have the
appearance of an east wind. Lieutenant Maury adopts the same
explanation. It is, indeed, that of Halley, slightly modified.

The warm air, ascending from the equatorial regions, rushes to the
poles to be cooled in turn, sliding over the heavy strata of cold air
below.

The northern trade-wind prevails in the Pacific between 2 deg. and 25 deg. of
N. Latitude; the southern trade, between 10 deg. and 21 deg. of S. Latitude.
In the Atlantic the trades are generally limited by the 8th and 28th
degrees of N. Latitude. The region of calms lies between these trades,
and beyond them are what are styled the Variables. In the former the
seaman finds baffling winds, rain, and storms. Occasionally, from
causes not yet fully explained, north and south periodical winds break
in upon them, such as the Northers which rage in the Gulf of Mexico.

There are many curious facts connected with the Trades, and with the
Monsoons, or trade-winds turned back by continental heat in the East
Indies, the Typhoons, the Siroccos, the Harmattans, land and sea
breezes and hurricanes, the Samiel or Poison Wind, and the Etesian.
The Cyclones, or rotary hurricanes, offer a most inviting field for
observation and study, and are an important branch of our subject. But
we are obliged to omit the consideration of these topics, to be taken
up, possibly, at some other opportunity. The theory of the Cyclones
may be justly considered as original with our countryman, Mr.
Redfield. Colonel Reid, Mr. Piddington, and other learned Englishmen
have adopted it; and so much has been settled through the labors of
these eminent men, that intelligent seamen need fear these storms no
longer. By the aid of maps and sailing-directions they may either
escape them altogether, or boldly take advantage of their outward
sweep, and shorten their passages.

We have yet to ascertain the causes of the many local winds prevailing
both on the ocean and the land, and which do not appear to be
influenced by any such general principle as the Trades or the
Monsoons.

The force of air in motion gives us the gentle breeze, the gale, or
the whirlwind. At one hundred miles an hour it prostrates forests. In
the West Indies, thirty-two pound cannon have been torn by it from
their beds, and carried some distance through the air. Tables of the
velocity of winds are familiar to our readers.

Let us next advert to the connection of the atmosphere with Vapor and
Evaporation. The vapor rising from the earth and the sea by
evaporation, promoted by dry air, by wind, by diminished pressure, or
by heat, is borne along in vesicles so rare as to float on the bosom
of the winds, sometimes a grateful shade of clouds, at other times
condensed and gravitating in showers of rain. Thus it enriches the
soil, or cools the air, or reflects back to the earth its radiated
heat. At times the clouds, freighted with moisture, present the most
gorgeous hues, and we have over us a pavilion more magnificent than
any ever constructed by the hand of man. These clouds are not merely
the distilleries of rain, but the reservoirs of snow and hail, and
they are the agents of electric and magnetic storms.

Notwithstanding their variety, clouds are easily classified, and are
now by universal consent distinguished as follows.

In the higher regions of the air we look for the Cirri, the Curl
Clouds. They are light, lie in long ranges, apparently in the
direction of the magnetic pole, and are generally curled up at one
extremity. They are sometimes called Mackerel Clouds. They are
composed of thin white filaments, disposed like woolly hair, feather
crests, or slender net-work. They generally indicate a change of
weather, and a disturbance of the electric condition of the
atmosphere. When they descend into the lower regions of the air, they
arrange themselves in horizontal sheets and lose much of their
original type. The Germans call them Windsbaeume, or wind-trees.

The Cumulus is another form of cloud, which floats along in fleecy
masses, in the days of summer, but dissolves at night. Sometimes it
resembles a great stack or pile of snow, sometimes it has a silvery or
a golden edge, as if we saw a little of the lining. Sometimes they lie
motionless in the distance, and are mistaken by mariners for land.
They rest upon a large base, and are borne along by surface-winds.
Their greatest height is not more than two miles. They carry large
quantities of moisture with them, and, when preceding rain, fall
rapidly into other shapes.

The Stratus, or Fall Cloud, is horizontal in its figure, lies near the
earth, and its length is usually greater than its breadth. It floats
in long bands with rounded or sharpened points, and is seen rising
from rivers or lakes, at first as a fog. In the morning it indicates
fine weather. The Fall Cloud never discharges rain.

This comes only from the Nimbus, which is quite unlike the others. It
puts on a dark gray color, has irregular transparent edges, and
increases rapidly so as to obscure the sky. It appears to absorb the
other clouds, to be a union of their differently electrified
particles, which are attracted to each other, form drops of water, and
descend as rain.

Of the first three forms we have three modifications or varieties. The
Cirro-Cumulus is a congeries of roundish little clouds in close
horizontal position, varying in size and roundness, and often, to use
the words of the poet Bloomfield, appearing as "The beauteous
semblance of a flock at rest."

The Cirro-Stratus is more compact than the Cirrus,--the strata being
inclined or horizontal. It is sometimes seen cutting the moon's disc
with a sharp line. The Cumulo-Stratus, or Twain Cloud, is denser than
the Cumulus, and more ragged in its outlines. It overhangs its base in
folds, and often bears perched on its summit some other form of cloud,
which inosculates itself with it. Sometimes a Cirro-Stratus cloud
comes along and fastens itself to it parasitically. It is one of our
most picturesque forms of clouds.

Within the last two years we have twice observed in the city of New
York, during the summer afternoons, large masses of clouds coming over
from the southwest, and hanging rather low, which could not be well
placed in any of the classes already described, or recognized as such
by meteorologists. They consisted of a great number of hemispherical
forms of large diameter, hanging vertically from a Stratus cloud or
plane above them, and to which they appeared attached. They were
regular in shape, and very distinct; they barely touched each other,
and were of a gray color. They might be compared to a hay-field turned
upside down, with innumerable hay-cocks hanging below it.
Unfortunately, the circumstances under which the spectacle was
observed did not; admit of any resort to the barometer, thermometer,
or anemometer. Should further observations verify these remarks, it
might perhaps be proper to style this variety the Hemispherical.

* * * * *

Dew is another atmospheric product. It is the condensation of the
warmer vapor of the atmosphere, in calm and serene nights, and in the
absence of clouds, by the cold surface of bodies on which it rests. In
some countries it is copious enough to supply the want of rain. The
earth radiates its own acquired heat, grows colder than the
atmosphere, and so condenses it.

What is thermometrically called the dew-point is that degree at which
the moisture present in the atmosphere, on being subjected to a
decrease of temperature, begins to be precipitated or condensed. It is
the same as the point of saturation. Daniell calls it "the constituent
temperature of atmospheric vapor." It is our criterion for
ascertaining how much moisture there is in the air, and at what degree
of heat or cold it would be precipitated. When the air is saturated, a
dry bulb and a wet bulb will read alike.

The dew-point has been a puzzle to most persons. Very few treatises
explain it satisfactorily. The definition just given, though explicit,
is not quite enough. For it will be perceived that an ordinary
subtraction of the degrees of temperature on a wet thermometer, which
had cooled down by evaporation, from the actual temperature indicated
by a dry thermometer, will not give us the dew-point.

For example,--if a free or dry thermometer indicates 63 deg., and the one
with the wet bulb has by evaporation cooled down to 54 deg., the
difference would be 9 deg.. The dew-point would not be 54 deg., but that
degree to which the mercury would fall in the free thermometer, for
the atmosphere to become saturated with the quantity of moisture then
actually existing in it. It would be 46.8 deg..

This dew-point, which figures so largely in all well-kept
meteorological reports, is the key to many important conditions of the
atmosphere, affecting health, vegetation, and climate.

It is found that the air at different degrees of heat has different
degrees of elasticity, different degrees of tension, and different
degrees of capacity to hold vapor. Dalton, by a series of experiments
with barometer-tubes, into which he introduced air and vapor at
certain temperatures, found what its force was upon the mercurial
column from degree to degree. He also experimentally determined the
ratio of the weight of moisture and of air, the former being five-eights
of the latter,--in other words, how many grains of moisture
additional could be held by the air, advancing from degree to degree
of temperature. This being ascertained, a table of factors was
constructed, in other words, a set of figures contrived, which should,
by a multiplication of the subtracted difference between the range of
the dry bulb and the wet bulb of the thermometers, furnish the amount
of deduction from the former which would indicate the dew-point, or
the point to which the mercury in the dry thermometer must fall to
show how much more moisture the air could hold without its
condensation. These tables of factors have been constructed at the
Greenwich Observatory, and are generally used.

The Hygrometer, invented by Mr. Daniell, gives the dew-point by
inspection.

It is an error to suppose that dew falls like rain from the air; it
forms on the body which is cooled down below the temperature of the
air. It differs in quantity with the radiating or cooling surface;
that which has absorbed and retained the most heat during the day
radiates the most at night and furnishes the most cold in return.

Hoar-frost, such as we find on our window-panes, or on the grass, is
the moisture of the warm air cooled down and frozen, and is produced
when the cold at the surface is below the freezing-point. What we in
common parlance call the action of frost, and which in this climate is
well known to be very powerful, is not particularly injurious to
organized bodies.

Mists are the vapor near the ground rendered visible by the
temperature of the air falling below that of the vapor. When we see
our breath in a cold morning, we see a mist. Where the surface is
comparatively warm and damp, and the air is cooler, we have mists,
which, if dense, are called fogs. These are found plentifully on the
banks of Newfoundland; and with icebergs on the one hand and the Gulf
Stream on the other, we must always expect to have them.

The distribution of rain, which is one of the offices of the clouds,
is another of the more important features of Meteorology. The amount
of water taken up by evaporation into the atmosphere is almost
incredible. It is calculated by Lieutenant Maury that there is
annually taken up in the torrid zone a belt of water three thousand
miles in breadth and sixteen feet deep. Rain occurs regularly and
irregularly in different parts of the earth. In some places it may be
calculated upon to a day; in others it is quite unknown. Latitude and
longitude may indicate the points of distribution, but the causes are
dependent on temperature, winds, locality, and, what may seem a
strange assertion, upon the conduct of man himself. The greatest
quantity falls near the equator, diminishing towards the poles.
Much more falls on islands and coasts than in the interior of
continents,--more in the region of the variables and less in that of
the trades. There are, however, tropical countries of great extent
where rain is scarcely ever seen.

The influence of man upon rain is seen in the progress of
civilization, the destruction of forests, and the drying-up of meres,
swamps, and water-courses.

Forests undoubtedly affect the distribution of rain, and the supplies
of streams and springs. Their cooling influence precipitates the vapor
passing over them, and the ground beneath them not getting heated does
not readily evaporate moisture. Lands, on the contrary, which are
cleared of forests become sooner heated, give off larger quantities of
rarefied air, and the passing clouds are borne away to localities of
greater atmospheric density.

The Canary Islands, when first discovered, were thickly clothed with
forests. Since these have been destroyed, the climate has been dry. In
Fuerteventura the inhabitants are sometimes obliged to flee to other
islands to avoid perishing from thirst. Similar instances occur in the
Cape Verdes. Parts of Egypt, Syria, and Persia, that once were wooded,
are now arid and sterile deserts.

In the temperate zones these results are not so immediately apparent.
It is now much in doubt whether the climate of our country has changed
its character within the last two hundred years. Jefferson and Dr.
Rush both contended that it had. Our oldest inhabitants assert that in
their day our winters began nearly two months earlier than they do
now.

The general laws laid down in relation to rain are these:--

1. It decreases in quantity as we approach the poles.

2. It decreases as we pass from maritime to inland countries.

3. It decreases in the temperate zones on eastern coasts as compared
with western coasts, but within the tropics it is the reverse.

4. More rain falls in mountainous than in level countries.

5. Most rain falls within the tropics.

* * * * *

The rainless regions, not deserts, are parts of Guatemala, the table-land
of Mexico, the Peruvian coast, parts of Morocco, Egypt, Arabia,
Persia, etc.

The electric character of the air is another subject of interest, and
a leading one in Meteorology. What can be more magnificent, what more
awful, than those storms of lightning and thunder which are witnessed
sometimes even in our own latitudes?

Faraday, who as a chemist and philosophical writer is of the highest
authority, professes to have demonstrated that one single gram of
water contains as much electricity as can be accumulated in eight
hundred thousand Leyden jars, each requiring to charge it thirty turns
of the large machine at the Royal Institution.

It is not intended that this astounding statement should be received
without some grains of allowance; but a very elegant and scientific
writer, who adopts it without hesitation, adds, "We can from this
crystal sphere [of water] evoke heat, light, electricity in enormous
quantities, and beyond these we can see powers or forces for which, in
the poverty of our ideas and our words, we have not names."

Flashes of electricity have been detected, during warm, close weather,
issuing from some species of plants. The Tuberose and African Marigold
have been seen to emit these mimic lightnings. (Goethe is the
authority for this.) To atmospheric electricity we doubtless owe the
coruscations of the Aurora, one of the most beautiful of our meteors.

The usual forms of lightning are the zigzag or forked sharply
defined,--the sheet-lightning, illuminating a whole cloud, which it
seems to open,--heat-lightning, not emanating from any cloud, but
apparently diffused through the air and without report. There are also
fireballs which shoot across the sky, leaving a train often visible
for seconds and minutes. These last, when they project any masses to
the earth, are termed aerolites.

Atmospheric electricity has much to do with the distribution of rain,
the precipitation of vapor, the condition of our nervous system, and,
according to Humboldt, with the circulation of the organic juices.
Atmospheric electricity has heretofore been a great obstacle to the
success of the Magnetic Telegraph, and curiously disturbs its
operation; but there has recently been invented an instrument called a
Mutator, which is connected with the wires, and carries off all the
disturbing influences of the atmosphere without interfering with the
working current. On the other hand, artificially created electricity
has led to important advances in many of the arts and sciences.

Ice is water frozen under a very curious and peculiar law. Hail is the
congelation of drops of rain in irregular forms, always sudden,--by
some attributed to electricity and currents of air violently rarefied
by it, and by others to rain-drops falling through a cold stratum of
air and suddenly congealed. Snow, the ermine of the earth, is the
crystallized moisture of the air, and is in subjection to unchanging
laws.

Water contracts as it grows colder, until it falls in temperature to
42 deg.. It then expands till it reaches 32 deg., when it becomes solid,
though its density is actually diminished, and its specific gravity is
reduced to .929, while that of unfrozen water is 1.000. Of course it
is much lighter, and it floats. This admirable arrangement prevents
our rivers being frozen up and our lakes becoming solid. Ice thickens
because it is porous, and allows the heat of the water to pass up and
the cold to descend; but this is happily a slow process, as ice is a
bad conductor. Salt water freezes at the temperature of 7 deg., 25 deg. below
freezing-point. There are many things to be said about ice, whether as
glaciers, or Arctic bergs, or, as it is found sometimes, contrary to
its general law, at the bottom of rivers and ponds, its geological
movements in the transportation of boulders, and as an article of
luxury;--but we are compelled to leave them for the present.

Snow, which, in its crystallization, surpasses the most perfect gems,
is invariably found arranged in determinate angles, to wit, 60 deg., and
its double, 120 deg., and formed of six-sided prisms. More than one
hundred kinds have been described by Dr. Scoresby and others, and all
these are combinations of the six-sided prism. The uses of snow, from
its non-conducting qualities, whether as appreciated by the Esquimaux
as a material for huts, or by the agriculturists of our own climate as
sheltering the seed, are too well known to require any particular
remarks. Strange as it may appear, the proximate cause of the
formation of snow is not yet fully agreed upon by the learned.

The connection between Sound and the atmosphere is an important one.
The air is a conductor of sound, and in some conditions one of the
best. A bell rung in an exhausted receiver gives no sound. In the
Arctic regions ordinary conversations have been distinctly heard for
the distance of a mile and a half.

All that we have thus far said in this article bears directly, in some
form or other, on another of the great features of Meteorology, one of
its great objects, and an unceasing topic,--namely, Climate.

The term Climate, in its general sense, indicates the changes and
condition of the atmosphere, such as we have been considering. It has
something to do with all of them; it is not entirely controlled by
any. Thus, places having the same mean annual temperature often differ
materially in climate. In some (we quote Mrs. Somerville) the winters
are mild and the summers cool, whereas in others the extremes of heat
and cold prevail.

Climates are not found coincident with lines of latitude; they are
quite as often found parallel to lines of longitude. If you connect
the extreme points of the mean annual temperatures by a line passing
round the earth, you have a zone, but never a true circle. The curves
are longitudinal.

Climate is dependent on temperature, winds, the elevation of land,
soil, ranges of mountains, and proximity of bodies of water; and it is
also the expression, if we may so term it, of the changes in the
atmosphere sensibly affecting our organs. Humboldt refers it to
humidity, temperature, changes in barometric pressure, calmness or
agitation of the air, amount of electric force, and transparency of
the sky.

When mountains range themselves in lines of latitude across a
continent, they are barriers to civilization, to the mingling of
races, and the union of states. Thus, the Pyrenees have always kept
France and Spain apart, the Alps and the Apennines have secluded
Switzerland from its neighbors. In our own country, Providence has
placed our great mountains on a northern and southern axis; the
slopes, the direction, the prevailing winds, the facilities for
transportation and travel favor no one of our northern, southern, and
western States more than another.

Climate affects vegetation and the distribution of animal life, and
thus greatly modifies commerce.

Whatever of importance is accomplished in those countries where
climate has overpowered a race is best and principally done by the men
of the temperate zones, who carry with them perseverance, courage, and
ability, and maintain their ascendency, true to their type, while they
have their life to live.

But with our own eyes we may perceive how much climate affects
agriculture. The humidity or dryness of soils, their natural or
acquired heat or cold, the prevailing winds, the quantity of rain, the
snows, the dews, all affect the planter of the seed and the tiller of
the ground; they increase or diminish the aggregate of the products of
countries, the value of their imports and exports,--in short, their
material power, their resources, their influence, their very
existence.

The climate of our own country is exceedingly variable. The
transitions from heat to cold are very sudden, the range of the
mercury is very great. In the North, we have almost the Arctic
winters; in the South, almost the peculiarities of the tropics. Of the
State of Pennsylvania it has been said, that in this respect it is a
compound of all the countries in the world. Mr. Jefferson and Dr.
Rush, as before observed, insisted that our climate has changed; and
Williams, the historian of Vermont, contends that New England has
deteriorated in its seasons, temperature, harvests, and health, since
its early settlement. Our winds blow from every point of the compass,
but a due north wind is very rare. Our great western lakes have a
large influence on our climate. Some learned men have asserted, that,
if they were land, their area being about ninety-four thousand square
miles, the region would be so cold as to be scarcely inhabitable.

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