Atmospheric phenomenon

“ Thus the heated air makes its way from the equator to the poles in the upper regions of the atmosphere, while the cold air makes its way from the poles to the equator along the lower regions. Very often, too, aqueous vapour as well as air is carried up by means of the sun’s heat to the upper and colder atmospheric regions, and there deposited in the shape of rain, or hail, or snow, which ultimately finds its way back again to the earth, often displaying in its passage immense mechanical energy. ”

“ In the atmosphere the counterpart of our sheet is a layer, several miles in depth, of minute particles, which by day are lighted up by the sun. Some of the particles are tiny dust motes, others are fine droplets of water or bits of ice, and the rest are the molecules of the atmospheric gases themselves. It is the light that comes to us from these particles that makes our eyes insensitive to the fainter light of the stars, and makes the sky itself a visible luminous vault. ”

“ He will find that the centers of the Lows will follow closely the direction indicated by the isotherms that lead eastward out of their centers, and that they move across the country from the west in quite regular succession, and that the frequent changes from sunshine to clouds and from warm to cold are the result of the mixing of the air by these atmospheric eddies. ”

“ The word ‘atmosphere’ is of Greek origin, and signifies a body of vapour in a spherical form. The rapidity of atmospheric air cannot be explained on any principle but its fluidity; therefore atmospheric air, the permanently elastic fluid which surrounds the earth, although invisible, may be said to be material, and to possess all the common properties of matter; for it occupies space, attracts and is attracted, and consequently has weight. ”

“ In these movements and their causes we have the general outline of our subject, within which we must now sketch the weather. The causes of atmospheric movement, which we have thus far considered, are the unequal distribution of the sun's heat, the absorption and precipitation of moisture, the direct and the inductive action of the earth's rotation and friction. If to these we should add the tidal action of the sun's and moon's attractions, we should perhaps complete the list of vera causae which are certainly known to exert a more or less general influence upon the atmosphere. ”

“ But the illustra tion of the principle on the broadest scale is the system of atmospheric circulation known as the equatorial and polar currents of the atmosphere, which originate in the unequal heating by the sun of the equatorial, temperate, and polar regions. The other principal motive force in atmospheric circula tion depends on the aqueous vapour. ”

“ Of the heat that comes to us from the sun, it is estimated that more than one-third is reflected by clouds and the earth, or scattered by dust and air molecules, and thus passes back into space without having had any effect in heating the atmosphere. ”

“ The atmospheric circulation, then, may be readily regarded as the movement, over the terrestrial surface, of gaseous masses which absorb and return energy in regions of high and low velocity exactly in the fashion explained above for solid material. ”

“ But the air thus warmed by the earth is in continual motion owing to changes of density. It rises up and flows off, owing to the greater weight of the cooler air which forces it up and takes its place; and thus heat can never accumulate in the atmosphere beyond a very moderate degree, the excessive sun-heat of the tropics being much of it carried away to the upper atmosphere and radiated into space. ”

“ It is not enough that we have the evaporation of moisture that will ascend into the higher regions of the air and there be condensed into cloud and possibly rain, but we must have the means for distributing these conditions over a large area, and for this purpose we have the phenomenon of wind. Why the winds blow can be accounted for to a certain extent,—we might say to a large extent,—but there yet remain many unsolved problems relating to wind and weather. Of the phenomena of wind we will speak more fully in a future chapter. ”

“ For example, an increase of heat from the sun may produce increased evaporation from certain water areas of the earth's surface, and the moisture thus drawn up being carried away by the movements of the atmosphere, may be deposited elsewhere in the form of snow or rain. It is almost impossible without a much more intimate knowledge of the laws governing the movements in our atmosphere to say in advance what the effect of a slow and periodic change in the sun's heat will be. ”

“ The motion of the atmosphere is brought about by the action of heat here and there, and in a trifling way, by the heat from the interior of the earth escaping through hot springs or volcanoes, but almost altogether by the heat of the sun. If we can imagine the earth cut off from the solar radiation, the air would cease to move. We often note how the variable winds fall away in the nighttime. ”

“ As the earth would everywhere and at all times be covered with a deep stratum of cloud there would be little loss of heat to space by radiation and the temperature would be excessive, rising in the tropics to near the boiling point. We will assume that the atmosphere would reach a stable and unchanged condition of great heat and humidity and be without motion or precipitation. ”

“ Our atmosphere, charged with aqueous vapour, serves to shield us from the intense action of the solar powers. By it we are protected from the destructive influences of the sun’s light and heat; enjoy those modified conditions which are most conducive to the healthful being of organic forms; to it we owe “the blue sky bending over all,” and those beauties of morning and evening twilight of which
—— Sound and motion own the potent sway. ”

“ Heat rarifies atmosphere as we here realize by the influence of the sun. If the addition of a few rays of the sun will dissipate the dense clouds, and so materially rarify our atmosphere at the distance of ninety-five millions of miles, what may we suppose the condition of the atmosphere ninety millions of miles nearer its source? ”

“ The only important extra-terrestrial factor of climate is the amount of radiant energy which reaches the borders of the earth’s atmosphere from the heavenly bodies—that is, from the sun, for the moon and stars can be ignored in this connexion. ”

“ The consideration of the weather enables him to understand the state of the atmosphere about him, its effect on climate, the cause of storms, and the different action of solar energy on air, land, and water, which renders possible life upon the earth. ”

“ There is another, and perhaps more powerful cause, I suspect, which may occasion the great cold on mountains, and in the higher parts of the atmosphere, and which has not yet been attended to; I mean that the fluid matter of heat may probably gravitate round the earth, and form an atmosphere on its surface, mixed with the aerial atmosphere, which may diminish or become rarer, as it recedes from the earth's surface, in a greater proportion than the air diminishes. ”

“ Thus the heated current moves more easily and rapidly than the colder; and the latter, consequently, turns back a portion of what was going towards the poles, and adjusts the equilibrium of the atmosphere. I have already shown you the great importance of the circulation of the air in the economy of nature; and how, among the many offices of the atmosphere, it distributes moisture over the surface of the earth, making the barren places fruitful, and tempering the climates of different latitudes, fitting them as the abode of civilised man. ”

“ Taking the analogy of our atmosphere in its relation to the earth, we know that when heat is absorbed by it, it expands, the result being that a greater pressure is exerted by the expanding atmosphere, than would be exerted if it remained at the same temperature all the time. ”

“ The atmosphere flows in a grand harmonious system of currents and counter-currents, with their corresponding eddies, just like the ocean; and the grand final results of its varied action are to equalise in some degree the temperatures of the world, to carry off and distribute moisture where it is required, to sweep away noxious vapours, and generally to ventilate the Earth and gladden the heart of man.
The primary cause of all wind is the combined action of heat and cold. ”

“ No dust is lifted high into the air to lend it a distinct colour; Only the dazzling white reflex from the clouds reaches the outside space and gives the planet its remarkable, brilliantly white, lustre. The powerful air currents in the highest strata of the atmosphere equalize the temperature difference between poles and equator almost completely so that a uniform climate exists all over the planet analogous to conditions on the Earth during its hottest periods. ”

“ But of all recognized branches of science, that which treats of the atmosphere—meteorology—is at the present time certainly the most backward. The reasons are not far to seek. The air is invisible, and in its upper regions inaccessible. ”

“ The solid globe of the earth is enveloped in a mixture of gases, principally oxygen and nitrogen, which we call the air, or the atmosphere, and upon whose presence our life and most other forms of life depend. The atmosphere is retained by the attraction of the earth, and it rotates together with the earth. If this were not so—if the atmosphere stood fast while the earth continued to spin within it—a terrific wind would constantly blow from the east, having a velocity at the equator of more than a thousand miles an hour. ”

“ No gas that would be likely to remain in the air would interfere with sight; water vapour is the only thing that could; and though the crust of this planet, even near the surface, is still hot, the sun being so distant, the vapour would not be raised much. By avoiding low places near hot springs, we shall doubtless have very nearly as clear an atmosphere as on earth. What does surprise me is the ease with which we breathe. ”

“ The atmosphere in motion is wind, with which the sailor has so much to do, and it behooves him to understand, not only the causes which produce it, but the laws which control it. “Whence cometh the wind, and whither goeth it?” It comes from heat, and as the sun is the father of heat, he is the father of the winds. Let us suppose the earth, and atmosphere both to be created, but not yet the sun. The atmosphere, being of equal temperature throughout the earth, would be in equilibrium. It could not move in any direction, and there would not be the slightest breeze to fan the brow. ”

“ This points to a chief acting force on which the great movements of the atmosphere depend, viz., simultaneous local irregularities in the distribution of temperature in the atmosphere. The local expansion of the atmosphere by heat during the day is greatest over land, where the air is clear, dry, and comparatively calm, and least over the ocean, where the sky is clouded, and the air loaded with moisture. ”

“ The whole atmosphere must have increased in quantity, because it appears by the barometer that there exists one-fifteenth part more air over us for many weeks together, which could not be thus accumulated by difference of temperature in respect to heat, or by any aerostatic laws at present known, or by any lunar influence. ”

“ But in the higher atmosphere, clouds can be formed by the action of the sun’s rays on certain gases. This is a great boon to us on the earth; for it assures us of clouds being ever existing to defend us from the sun’s extra-powerful rays, even when our atmosphere is fairly clear. ”

“ The heat of the sun, by its intense vibrations, comes to the earth dowered with a power which pierces the miles of our atmosphere, but if our air were as pervious to the heat of the earth, this heat would flyaway every night, and our temperature would go down to 200° below zero. ”

“ You now produced for yourself in miniature a storm and wind. The air that has been heated rises over a heated area, and cooler air from all directions around is passing into the space underneath the chimney and taking the place of the heated air that has gone up. This experiment illustrates what takes place, except on a smaller scale, out in the atmosphere when a portion of the earth becomes heated. ”

“ It is the work of that invisible, imponderable, omnipresent, and wonderful agent called heat. This is the agent which controls both sea and air in their movements and in many of their offices. The average amount of heat daily dispensed to our planet from the source of light in the heavens is enough to melt a coating of ice completely encasing the earth with a film 11⁄2 in. ”