_(FROM PART XIV. OF KNOWLEDGE FOR THE PEOPLE; OR, THE PLAIN WHY AND
BECAUSE.)_
_Why may the atmosphere be termed a fourth kingdom of Nature?_
Because it extends its influence in an equal degree over the three
kingdoms, the animal, the vegetable, and the mineral, operates upon
each after a distinct manner, and appears rather to be independent,
and allied to all of them, than to be rightly included within any one.
_Why is a knowledge of the atmosphere important to the naturalist?_
Because it serves to throw much light on the history and functions
both of the animal and vegetable creation; for it is through this
great medium that heat, light, electricity, oxygen, and the great
springs of vital phenomena, are conveyed to all classes of organized
matter. It is by means of this wonderful agent, that we gain the
theory of respiration in all classes of creatures possessing animal
life; and that we become acquainted with the migrations of animals,
as well as many of their peculiar instincts and habits. It is the
atmosphere that enables us to account for the periodical changes in
the plumage of birds and the furs of animals, and the variety of
colours to be found amongst them. By means also of the elasticity of
the atmosphere, sounds and odours are transmitted to sensitive beings.
Atmospherical phenomena, it may be safely inferred, attracted the
observation of mankind in the earliest ages: we know that the
Egyptians and the Greeks wrote upon the subject; the Jews too, a
pastoral people, "could discern the face of the sky;" and even in our
day, shepherds may be ranked among the weather-wise. "This is a fine
morning, a soft day, or a cold evening," are modes of salutation with
us, as commonly as is the "Salem Alikem" (Peace be with you!) amongst
the inhabitants of the more serene countries of the East. Shenstone
says, though with nearly equal spleen and truth: "there is nothing
more universally commended than a fine day: the reason is, that people
can commend it without envy."
_Why do we call the atmosphere a fluid?_
Because it has a tendency to move in all directions, and consequently
rushes in and fills every space not previously occupied by a more
solid substance. Hence we find, that every cave, crevice, place, and
vessel, having communication with the atmosphere, if it be not filled
with something else, is filled with air; against which it is no
argument that we do not see it, as it is perfectly transparent, and
consequently invisible.
_Why do birds fly?_
Because of the inertia of the atmosphere, which gives effect to their
wings. Were it possible for a bird to live without respiration, and in
a space void of air, it would no longer have the power of flight. The
plumage of the wings being spread, and acting with a broad surface
on the atmosphere beneath them, is resisted by the inertia of the
atmosphere, so that the air forms a falcrum, as it were, on which the
bird rises, by the leverage of its wings.
_Why is air generally considered to be invisible?_
Because, though a coloured fluid, and naturally blue, its colour
acquires intensity only, or, in other words, becomes visible only,
from the depth of the transparent mass. According to rigid Newtonians,
air is transparent, or, rather, invisible; and the azure colour of the
atmosphere arises from the greater refrangibility of the blue rays of
light. Other philosophers imagine that the blue tint is inherent in
air; that is, that the particles of air have the property of producing
a blue colour, in their combination with light.
_Why are the most distant objects in a prospect of a blue tinge?_
Because their colours are always tinted by the deepening hues of the
interjacent atmosphere. Again, the blending of the atmospheric azure
with the colours of the solar rays, produces those compound and
sometimes remarkable tints, with which the sky and clouds are
emblazoned. Hence, the mountains appear blue, not because that is
their colour, but because it is the colour of the medium through which
they are seen.
_Why do the Heavens appear blue?_
Because of our looking at the dark vacuity beyond our atmosphere
through an illuminated medium. Were there no atmosphere, it is
universally admitted the appearance would be perfectly black, except
in the particular direction of the sun, or some other of the heavenly
bodies, and since the atmosphere is transparent, this blackness (if
such an expression may be used) must be seen through it, only somewhat
modified by the rays of light reflected by the atmosphere to the eye,
from the direction in which we look. For this reason, the clearer or
more transparent the atmosphere is, the darker is the appearance of
the heavens, there being then less light reflected by the atmosphere
to the eye. In the zenith, the appearance is always darker than nearer
the horizon; and from the tops of high mountains, the heavens in
the zenith appear nearly black.--_Mr. B. Hallowell, in the American
Journal of Science and Arts._
_Why does the heat of temperature of different parts of the earth
vary?_
Because of the position of the place with respect to the equator, or
rather to the ecliptic, or, more strictly still, with respect to the
plane in which the earth revolves around the sun; for on this relation
depends the temperature of the place, so far as it is produced,
directly, by the influence of the sun. Maltebrun ascribes to it the
following influences: 1, the action of the sun upon the atmosphere: 2,
the interior temperature of the globe: 3, the elevation of the earth
above the level of the ocean: 4, the general inclination of the
surface, and its local exposure: 5, the position of its mountains
relatively to the cardinal points: 6, the neighbourhood of great seas,
and their relative situation: 7, the geological nature of the soil: 8,
the degree of cultivation, and of population, at which a country has
arrived: 9, the prevalent winds.
_Why are the strata of air upon all mountains of successive coldness?_
Because the air does not acquire immediately, by the passage of the
solar rays, a considerable degree of heat. Thus, with the elevation of
land, cold may be said to increase in very rapid progression. Winter
continues to reign on the Alps and the Pyrenees, while the flowers of
spring are covering the plains of northern France. This beneficent
appointment of Nature considerably increases the number of habitable
countries in the torrid zone. It is probable, that at the back of the
flat burning coasts of Guinea, there exist in the centre of Africa,
countries which enjoy a delightful temperature; as we see the vernal
valley of Quito, situate under the same latitude with the destructive
coasts of French Guyana, where the humid heat constantly cherishes the
seeds of disease. On the other hand, it is the continued elevation
of the ground, which, in the central parts of Asia, extends the cold
region to the 35th parallel of latitude, so that in ascending from
Bengal to Thibet, we imagine ourselves in a few days transported from
the equator to the pole.--_Maltebrun._
_Why does the destruction of forests sometimes prove beneficial to a
country?_
Because a freer circulation of air is thus procured--but carried too
far, it becomes a scourge which may desolate whole regions. We have
a sad example of this in the Cape de Verde islands, not to mention
others. It is the destruction of forests, and not a supposed cooling
of the globe, which has rendered the southern part of Iceland more
accessible to the dreadful cold which is too often produced by those
masses of floating ice which are intercepted and detained by its
northern coasts.--Ibid.
_Why do mountains influence climates?_
Because, although they cannot prevent the general motions of the
atmosphere from taking place, they may, by stopping them in part,
render particular winds more or less frequent throughout a certain
extent of country. Maltebrun observes, there cannot be a doubt that
the Alps contribute in securing to Italy its delightful and happy
climate, its perpetual spring, and its double harvests.
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