Chapter XI: Part 11

To the south of Cerne the Carthaginian navigator saw the sea burn, as it were, with streams of fire. Pliny, in whom the miracle (miraculum, as he calls it) of the date-shell excited so lively an admiration, and who must often have seen the sea gleam with phosphoric light, as the passage proves where he mentions in a few dry words the luminous gurnard (_lucerna_) stretching out a fiery tongue, has no exclamation of delight for one of the most beautiful sights of nature. Homer also, who has given us so many charming descriptions of the sea in its ever-changing aspects, and who so often leads us with long-suffering Ulysses through the nocturnal floods, never once makes them blaze or sparkle in his immortal hexameters. Even modern poets mention the phenomenon but rarely. Camoens himself, whom Humboldt, on account of his beautiful oceanic descriptions, calls, above all others, the “poet of the sea,” forgets to sing it in his _Lusiad_. Byron in his _Corsair_ has a few lines on the subject:

“Flash’d the dipt oars, and, sparkling with the stroke,
Around the waves phosphoric brightness broke;”

but contents himself, as we see, with coldly mentioning a phenomenon so worthy of all a poet’s enthusiasm. In Coleridge’s wondrous ballad of _The Ancient Mariner_ we find a warmer description:

“Beyond the shadow of the ship
I watch’d the water-snakes:
They moved in tracks of shining white,
And, when they rear’d, the elfin light
Fell off in hoary flakes.

“Within the shadow of the ship
I watch’d their rich attire--
Blue, glossy green, and velvet black:
They coiled and swam, and every track
Was a flash of golden fire.”

These, indeed, are lines whose brilliancy emulates the splendor of the phenomenon they depict, but, even they are hardly more beautiful than Crabbe’s admirable description:

“And now your view upon the ocean turn,
And there the splendor of the waves discern;
Cast but a stone, or strike them with an oar,
And you shall flames within the deep explore;
Or scoop the stream phosphoric as you stand,
And the cold flames shall flash along your hand;
When, lost in wonder, you shall walk and gaze
On weeds that sparkle, and on waves that blaze.”

Or the graphic numbers of Sir Walter Scott:

“Awak’d before the rushing prow,
The mimic fires of ocean glow,
Those lightnings of the wave;
Wild sparkles crest the broken tides,
And dashing round, the vessel’s sides
With elfish lustre lave;
While, far behind, their vivid light
To the dark billows of the night
A blooming splendor gave.”

THE SEASHORE
--P. MARTIN DUNCAN

The seashore is the debatable ground where the sea is constantly striving to wear away the land. It is the present limit to the ocean and sea, and a little beyond, for it reaches inland further than the wildest waves and the highest tides can attain.

Where the seashore begins and ends is a matter of opinion; but all of it is influenced in some way or other by the sea. In some places, high cliffs or rocks keep the sea from driving in upon the land; they are lofty, and may reach for miles along the coast. The high tide comes up their steep faces for many yards, and when it retires a rocky strip is seen at their feet, and thence a breadth of rock, shingle, or sand leads down with a greater or less slope to the water’s edge. Here there can be no doubt how far the shore reaches inland, for the cliffs limit it. In other parts of our own and other maritime countries, there may be no high land on the coast; but marshes and low lands, with, or without sand-hills, form barriers to the incursion of the sea. The highest tides have their limit in those places, but the wash of the sea and the spray, together with the drainage of the sea into the land, make the water saltish for some distance inland, and the earth close by is sodden with salt. Then, long stretches of mud or of sand form the slope, over which the sea rolls up to the land, and which is exposed and remains more or less wet at low tide.

In these low-lying parts of the coast the shore is not very distinctly separated from the land, and often miles of swamp, marsh, and sand-banks are invaded by the sea during storms and very high tides. The ditches near the sea contain salt or brackish water, and the whole of this kind of coast-line has a peculiar and desolate appearance. If these two kinds of coast are taken as the extremes, all the varieties of seashores will fit in between them; but still it will appear that while in some the limit between the land and the sea is very decided, in others it is not so.

Seaward the shore is very variable in its extent. In some places it may barely exist, or may only be a ledge of rock, between the cliff, the high land, and the water; and in others, miles of sand, shingle, and mud may be between the furthest reach of the waves and the limit of the low tide. The commonest examples of shores are those which are between these extremes. Some seashores slope very gradually to the sea and their extent is then usually great; and others, which are limited in their breadth, are more precipitous. Perhaps it is best to say that a seashore is the part of a coast which, at some time or other, is covered or uncovered by the sea; and that it has an extension inland, where the spray and wind are felt and act on the land, and also seaward, where some shore is only uncovered during excessively low tides. According to this view, it is possible to portion out a seashore into a greater or less number of breadths, which may be placed, side by side, from the land to the sea. First, a breadth will pass along the coast, and will contain the marshy, swampy land, or the hard rock down to the edge of the highest tide-mark. It may be miles across, or only a few feet in extent. Secondly, a breadth will be found between this last and the sea, where it is highest during common tides and storms. Thirdly, a breadth will exist four times in the twenty-four hours as dry land, and for the rest of the time it will be beneath the waves, and this is situated between ordinary high and low-tide marks. Finally, a breadth will be between this last and the everlasting sea; it is narrow, and is only uncovered for a few hours, in the months of the year when there are what are called “low spring tides.” These four breadths are termed zones, or belts; and in common language the first is the beach and coast-line, the second is the shore, the third is the tide-shore, and the fourth is “low spring shore.”

Differing in their extent, and in the nature of their surface, in every few miles of the coast of a maritime country like Great Britain, the zones have their peculiar animals and plants, and waifs and strays--the wreckage of the sea, of its floor, and of the coast-line. When the whole of the shore slopes very rapidly to the sea, the third and fourth zones are small in extent, but when the slope is gradual, they are large. And when the tide rises much and falls correspondingly, the third zone is usually uncovered but for a short time. The tide usually moves along the shore, and does not simply come in on to the land and recede; for one tide moves in one direction and the next in the opposite. Thus floating substances are carried along the coast for miles by the rising tide, and come back again, more or less, with the falling tide.

Tide, wind, and wave forever act on the surface of the zones, but their action is the greatest on those which are landward. There are other wreckers of the coast; for the heat of the sun, the winter’s frost, the rain, and the chemical action of the air, one and all crumble and break off pieces of rock or earth. These fall on to the tidal shore, and are rolled here and there, and up and down, to be turned into mud, sand, and pebbles. The cliffs and bold headlands are worn year by year, and during centuries they lose much, and retire landward. Needles and “no man’s lands” stand out on the shore, or out at sea, testifying to the former extension of the land; and shore exists where there was once high solid rock. The shore consists of the worn surface of the old land, rock, or earth, and this is usually hidden by stone or stuff which has fallen from the cliffs, and by sand, or mud, or pebble and stone, which the tide has swept along. But often the jagged or rounded remains of the former rock project out of the sand, mud, and stone on the shore, and they may be bare, or covered with sea-weed. In other spots, the hard rock is hollowed out into places which let the water stand in them like so many puddles, pools, and ponds, when the tide has gone down. These are often crowded with marine plants and animals of the shore. The rolling stones, the wash of the tide, and the rush and drawback of the waves, are ever wearing off the surface of the shore and grooving it, or planing it flat, and in some places where the stones do not collect, this is very evident; but where they form great masses of pebbles or shingle, it can not be readily seen.

There are many shores around Great Britain, where the rock is hard, which are rarely covered with pebbles, bowlders, and sand; and the sea-weed grows on them and protects them against the sea. But usually the rock is only exposed here and there, and the stones which collect and cover much of it come from a distance, and are on the move at every tide. In some places, where the coast is composed of clay or soft sandstone, the shore is muddy, soft, and may be uncovered or covered by stones.

The wear of the sea is but little seen in such places as this, and still less so where the coast is low and flat, and the shore is very extensive and the water is shallow for a long distance. In fact, on many of these flat shores, instead of erosion taking place, the sea is adding to the land by depositing. This is particularly the case at the entrance of great, and of many small rivers. Their mud collects in the shallows at their mouths, and is added to by sand and shingle, so that land grows seaward, instead of the reverse. The seashore is then, usually, uninviting and often consists of large mud flats. Again, in some localities, where much sand collects on the surface of the rock forming the seashore, it may be “quick” in many places. The rising tide gets under the sand, which suddenly becomes like so much sand and water, and the falling tide leaves it hard for a while. The ordinary condition of a sandy shore is either that of a number of very slightly rounded stretches of sand, with drainage-streams between them, or it is pretty hard, readily dug into, and marked on the surface by ripples. The ripple-mark on sand always strikes the observer; it represents little ripple-like waves, wonderfully regular, and each has a ridge and a valley. They are very lasting, but disappear on the slightest movement of the wet sand as the tide comes in. These little ridges and valleys are not found when the water covers the sand at a considerable depth, but they are especially seen between high and low spring-tide limit. Such marks can be made, artificially, with sand, for instance, on the bottom of a large basin. If some sand is placed on the bottom, and water be poured in, and the edge of the basin be pushed, a to-and-fro movement of the water will occur, and it will be continued down to the sand. As the motion ceases, the sand will be seen to collect in ridges, side by side, and they will be perfect when the motion stops. Motion of the sea-water in one direction over soft sand will not produce ripple-mark well, but a slight to-and-fro movement will do it to perfection. Infinitely more wonderful than these ripples are the pebble beaches, for they often extend for many miles, and have a very considerable thickness. Worn, in the first instance, from distant rocks, born of huge bowlders, which the mighty waves laden with rolling stones have broken down, the pebble is formed by rolling against others, and the result of its wear and tear is carried off in the form of sand. They travel miles and miles along the coast with the tide, and therefore it is very common to find one kind of rock forming the coast-line, and the shore close by having pebbles made up of stone which is not known to be near at hand. Thus, on the coast of South Devon, the red rocks form the coast-line; they are sandy, and are covered in some places by a beautiful green vegetation. The sea is often of the brightest blue, or gray, when the sky is not much tinted with color. But the sea covering the shore at high tide looks whitish, and this is produced by the white and light slate-colored pebbles which reach up close to the red rocks. They are not made up of red sand; on the contrary, they are of gray and bluish limestone, and come from rocks which are situated miles to the west. Further east, the Chesil Bank is seen, and it is an enormous shore of pebbles, which have been carried along the coast and have found an uncertain resting-place there. Every tide makes more sand out of the hardest pebbles, as they knock one against the other and wear away, and the sand already made scrubs them as it is hurried hither and thither by the waves. In some places where the sea is giving up rather than taking off land, the sand which is cast up may be the result of the wear of distant pebble-making, or it may be composed of myriads of broken tiny shells which once lived in shallow water.

It has been already stated that the sea is encroaching on the land in some parts of England, and that it does not do so in others, while it appears to be giving place to land elsewhere. In the first instance, the seashore must grow, as it were, must increase landward, and it really does so at different rates, in different parts of the country. In some parts of the coast a yard is lost every year and the sea comes in on the land so much the more. But all the space once occupied by cliff and rock is soon worn by the sea and is covered gradually by the tide, and after years have elapsed this _fore-shore_ is deepened seaward by the rolling stone and rushing waves, so that the visible beach or shore diminishes in size, unless a corresponding landward extension takes place. Although the cliffs and rocks fall, and their remains are swept away from the level of the shore, by currents, tides, and waves; yet, as has already been noticed, much of the ruined surface, leveled down as it has been, is covered up by relics of their wear and tear or by stone brought from a distance. It is only after some severe gale of wind, accompanied by a very high tide, that these stones and covering-up relics are swept away and the old rock-surface comes in view. All these matters are of importance, for the living creatures of the seashore depend upon the state of things, in each of the zones, for their ability to exist and flourish.

Where the coast has been low and the sea has gradually encroached, the remains of stumps of trees are often exposed after a gale. Then what is called part of a submarine forest is opened to the sight. There are many of them around England and especially on the coast of Norfolk and Essex, on the east; in many places on the south coast as far as Torbay; and on the west they are found in the Bristol Channel, and about Holyhead and the river Mersey. Sometimes it appears that the sunken forest has not been altogether produced by the encroachment of the sea on the land, and that sinking of the coast, or slipping of part of it, has caused the event. When the sea comes in on the land, it wears everything before it, and any forest land would in most instances be completely wrecked and the roots of the great trees would be worn and torn out of the soft earth and carried off to sea by the waves, tides, and currents. On looking at some smaller forests which are laid bare at very low tides, it is found that they consist of stumps of trees of great size, whose roots are still in the clay in which they grew, and a quantity of mud and sand is between the stumps and protects them from the usual action of water on submerged land. It appears that some movement of the earth’s crust had caused the coast to sink down, and then the sea invaded without wearing off the land. The trees were ruined by the sea-water, and broken off, and the mud, sand, and stone collected around the stumps.

It is not uncommon to see collections of stone and shells high up on the face of a rock or cliff, and when they are carefully examined they are found to resemble a bit of a shore or a piece of the beach, hoisted up many feet above the present line of the waves and tides.

They are called raised beaches, and they were formed by an upheaval of part of the coast with its shore during movements in the crust of the globe. There was a shore and a cliff, as there may be now, and the whole was pushed up some twenty, thirty, or more than a hundred feet beyond the reach of the highest tides and waves. In years past the waves broke upon the cliff beneath the upraised portion, and wore it away bit by bit; and then the air and sun acted with the rain in wearing it, and now only a portion remains.

Every coast-line is subject to these sinkings-down and upheavals, and of course a seashore is produced rapidly, and is made broad and shallow during the first kind of occurrence, and is stopped and has to be formed afresh during the last. As these remarkable movements of the outside of the globe are not universal, and affect some parts of a coast more than others, they will tend to give great variety to the seashores of a country. Together with the varying action of the tides, waves, and currents upon cliffs and rocks of different stones and earths, and of many hardnesses, these movements have made the shores of Great Britain very curiously varied in their size and character.

It must be remembered that as new shores are formed, or old ones are extended, the zones are kept within their bounds, and that as one zone creeps in on the land, those to the seaward move up also; so that where there was once a between-tide zone there may now be deep water. This change in the position of zones is very important; for certain animals and plants of the shore only live in certain zones, and their increase or decrease in numbers depends upon the corresponding state of their special locality.

III.--THE ATMOSPHERE

THE OCEAN OF AIR
--AGNES GIBERNE

Our earth has many robes. Closely-fitting garments come first, of brown soil or gray rock and green grass, with wide liquid underskirts of deep blue filling up the spaces between. Outside these are coverings more wonderful still; fragile, yet strong, transparent, almost invisible, folded around layer upon layer, or, as one might say, veil upon veil, each more gossamer-like than the last. These form earth’s surrounding atmosphere--a substance pervading everything, found everywhere. One may travel from the equator to the poles, one may journey by sea or by land, one may soar high in a balloon or descend deep into a mine, but one can never in this world go to a place where the atmosphere is not.

A substance--for air can be felt; air has weight; air occupies space; air, like any other body, can be made hot or cold; air is composed of particles of substantial matter. Air has a faint bluish tint, which on a sunshiny day becomes in the sky a very pure and deep blue. This tint is not believed to be the natural color of the atmosphere. Were it so, the air would merely act the part of a blue pane of glass, rendering the white light of the sun blue as it reaches our eyes; but the blue of the atmosphere is known to be a reflected blue.

If reflected, there must be something in the atmosphere to reflect it; and such indeed is the case. Perfectly pure air would doubtless be without color, but perfectly pure air we do not find. The whole atmosphere is full of multitudinous minute specks, so small as to be in themselves invisible, so light as to remain aloft. To the presence of these the blue tint is believed to be due. They scatter the light of the sun, and produce the blue effect.

A beam of strong white light, caused to pass through a liquid which contains a large supply of minute floating particles, is affected by them in a like manner. The short blue waves are more abundantly reflected than the long red waves; and so the water seems to be blue. This explanation serves for the deep-blue color of the ocean, as well as for the blue of the atmosphere.

The whole earth is surrounded by this marvelous air-ocean; an ocean of gaseous matter, at least one hundred times as deep as the water-ocean. At the bottom of the gaseous ocean we small human creatures crawl about, commonly on flat lower levels--the ocean bottom, in fact. Sometimes, with much toil and trouble, we climb the little ridges and mounds called “mountains”; little compared with the depth of the atmosphere, though not little compared with ourselves. The highest mountain-peaks of even the vast Himalayas lie low down near the bottom of the ocean of air.

But the very extent of the ocean of air adds to our difficulty in studying its nature. All observations that we can make must be limited by the state of the atmosphere just around ourselves. We can never get out of and beyond the atmosphere, so as to see it as a whole. At any time a slight local fog is enough to put a stop altogether to such observations, beyond the unpleasant experience of the fog itself.

It used to be supposed that the atmosphere reached only to a height of about fifty miles above earth’s surface. Of late years the opinion has gained ground that the atmosphere reaches to a height certainly of two or three hundred miles, probably of four or five hundred, possibly a good deal more. But the condition of the air far above is different from that of the air in lower levels, where we live and breathe. The higher we ascend, the more thin or “rare” becomes the air. A less quantity fills a certain space up there than down here. The particles float further apart one from another.

This difference in the density of the air is chiefly due to attraction. Each separate air-particle is drawn steadily earthward by the force of gravitation, and that force is stronger on the surface of earth than at a distance. The closer to earth, the heavier the pull; the further from earth, the less the pull. Besides the actual attraction of the earth drawing the air-particles downward, there is the great weight of the whole atmosphere above, caused by the same attraction. Miles and miles of air overhead press mightily downward, packing tightly together the lower layers of air near to earth’s surface.

Without this pressure of the overlying atmosphere, the air down here would not be nearly so dense as it is; and, indeed, would not be fitted to support life. A man ascending a mountain or rising in a balloon leaves heavy layers of air below, and has an ever-lightening weight above, so that the atmosphere around him becomes constantly more thin, more difficult to breathe.

In the beginning of the last century Humboldt made a vigorous attempt to scale Chimborazo, one of the loftiest of the Andes. He and his party suffered severely from sickness, giddiness, and difficulty in breathing, and the attempt proved a failure. Not till over seventy years later was the ascent actually accomplished by Mr. Whymper.

Carried upward passively in a balloon, without effort, men have risen higher than the highest mountains. Mr. Coxwell and Mr. Glaisher in their celebrated aerial voyage of 1862 are believed to have mounted seven miles above the sea. No little peril and suffering were involved, alike from the extreme thinness of the air, and from the bitter cold.

The voyagers suffered from severe “sea-sickness,” though not from bleeding of the nose or singing in the ears, popularly expected on such occasions. They had enough to bear without these additions. Mr. Glaisher held manfully to his task, observing and noting down the state of the atmosphere minute by minute, despite sickness, brain-pressure, violent headache, and a pulse at 108 per minute, all due to the rarity of the air.

In those lofty regions of the air-ocean no living creatures exist. The voyagers passed through boundless silent solitudes--silent except for the hurried beating of their own hearts, the sound of their own panting breath, the sharp ticking of their watches, and the “clang of the valve door.”

On leaving earth the thermometer stood at 59°. Soon afterward the balloon passed through masses of cloud, thousands of feet in depth, then came out into dazzling sunshine, with deep-blue sky above and countless mountain masses of billowy cloud below.

As they rose, they released at intervals a captive pigeon. One set free at a height of nearly five miles “fell downward like a stone.” Of two others taken higher, one died of the cold and the other was stupefied. When they reached five miles above the sea, the temperature was below zero.

Still upward, further upward, rose the resolute pair. Then blinding darkness and insensibility seized Mr. Glaisher. Had he been alone, he could never have revived. With no one to open the valve, the balloon must have carried him onward into yet higher and deathlier regions, where for lack of air he would have perished. Even then Mr. Coxwell did not at once give in; but he was strictly on the watch. At the seven miles’ level, a tremendous height, he too felt signs of failing consciousness. In a few minutes more all would have been over with them both, and at last he yielded. It was indeed time that he should. His hands were powerless to act, but he seized the valve rope in his teeth and pulled. The gas rushed out; the balloon steadily sank. Both lives were saved, and a mighty feat had been accomplished.

Yes, a mighty feat, and a tremendous height--in consideration of human powers! Seven miles high would seem to be the outside limit at which animals generally can exist for even a short time. Birds may be to some extent an exception. Certain birds are believed to soar occasionally two or three miles higher still.

But what are seven miles--what are even ten miles--compared with the four or five hundred miles of atmosphere-depth? With all our utmost efforts, we and the birds still find ourselves only able to creep and flutter on or near the floor of the ocean of air.

What earth would be without her surrounding ocean of air, we can scarcely imagine. The atmosphere plays so extraordinary and essential a part in all around, that to picture its entire absence is not easy. We see faintly on the moon something of what an airless world must be. Yet since we only “see” from a distance of two hundred and forty thousand miles, that does not mean much. Imagination has to come in, and imagination is apt to play us curious tricks when running after affairs which lie outside the range of human experience.

Without air, man and beast can not breathe. Without air, plants and trees can not grow. Without air, life as we know it--the lower animal life common to man and beast--is a thing impossible. Without air, our world would be, as we suppose the moon to be, a world of lifelessness.

Air is earth’s outer robe, “for use and for beauty”--for use in modes uncountable; for beauty, not so much in itself as in the softening, the diffusing, the controlling effects of its presence. Air is a mighty ocean, in which all things living must dwell. Even the living things of the sea are not exceptions to this rule, for water itself is pervaded by air. A man, going into and under water, does not get beyond the touch of air; only, not being provided, like fishes, with breathing gills, he can not make use of what is there--he can not separate the air from the water, and so keep himself alive by breathing it.

Some animals living in the water-ocean are as dependent upon the air-ocean as man himself for “the breath of life.” Whales are a remarkable example of this. They are not fishes, though often mistakenly called so, but belong to the same “family” of creatures as men and land-quadrupeds generally. A whale is warm-blooded, has no gills, and breathes atmospheric air, coming to the surface for it. A whale kept forcibly for a long while under water would be drowned exactly as a man would be. If a whale is thrown upon the shore, it does not die of suffocation, but of inanition. A fish’s gills are no more fitted to breathe air in bulk than a man’s lungs are fitted to breathe air diffused in minute particles through water. The fish out of water is suffocated by getting air too rapidly: the man under water by exactly the reverse. A whale breathes like a man, and on land it simply starves fast from lack of the incessant food required by such a huge carcass.

There is a difference certainly between man and whale in the matter of breathing. A man has to take in fresh supplies of air constantly, and if he is beyond reach of air for more than a few minutes he dies. A whale comes to the surface for about ten minutes, spouting out enormous supplies of used-up air and taking in enormous supplies of fresh air, after which it can remain under water for half an hour or more: some say an hour. Then a fresh bout of noisy breathing becomes an absolute necessity. This, however, is merely a matter of internal arrangement. The whale has an immense reservoir of blood, which, being thoroughly purified by the air during ten minutes of vigorous breathing, serves slowly to supply the creature’s requirements while below. But the need for air, and the effect of that air upon the blood, are much the same in man and whale.

Small creatures, as well as big ones, spending much time under water, and yet breathing air, have to come regularly to the surface.

If our world had no ocean of air, there could be on earth no men, no quadrupeds, no whales or fishes, no birds or insects, no forms of life.

Like the ocean of water, the ocean of air knows no repose or stagnation. What we call stillness on the most sultry of summer days does not mean absolute stillness. Though not enough wind may stir to lift a feather, yet the air is in ceaseless motion, to and fro, hither and thither. The whole atmosphere is a vast and complicated system of air-currents, and each lesser portion of air has its own lesser circulation. You can not lift your hand without causing a tiny breeze; you can not turn a wheel without making a minute whirlwind; and every separate air-movement draws other movements in its train.

There is water enough on earth for all needed purposes; but we should find ourselves in direful straits if the whole water-carrying from lakes and rivers for men and animals had to be performed by human agencies.

Far from this, a mighty apparatus is provided. The scanty aid that man can give only shows how little he is capable of. The entire atmosphere is a tremendous pumping engine, an enormous watering machine, always at work; always receiving supplies of liquid from the ocean, from seas, lakes, rivers; always showering this water down again upon the land, as needful drink for plants and animals, as needful cleansing for all things.

Air, the great carrier of water, in its wonderful strength and restlessness, bears vast layers of cloud to and fro, wafts away superfluous damp, drenches the dry and thirsty earth, fills ponds and lakes, feeds--nay, actually makes--the rivers, never flags in its ceaseless energy. If clouds hang low or fogs arise, we are glad of the moving air which sweeps them elsewhere. If the soil is caked and plants droop, we are glad of the moving air which brings rain. Thus our wants are supplied, and the wide water circulation of earth is carried on. Without circulation, without motion, stir, change, there can not be life. Stagnation must mean death. Our earth, without her ocean of moving air, would be a world of death.

Without air, earth would be in great measure a soundless world. Silence would reign here, as probably it does reign on the moon. Sound, as it commonly reaches our ears, depends for its very existence upon air. Let the concussion of two bodies be ever so mighty, if there were no air to bear away the vibrations of that concussion, there could be no crash of sound. True, sound-waves can be conveyed through a liquid or through a solid as well as through air; and we might be conscious of the ground’s vibrations, but our ears would hear no noise.

So an airless world would be a silent world. Without air, supposing we could ourselves exist, we should hear no trickling brooks, no rush of waterfalls, no breaking ocean waves, no sighing of the wind, no whisper of leaves, no singing of birds, no voices of men, no music, no thunder, no one of the thousand concomitant sound-waves which together make up the babble and murmur of country and town. Those only who are perfectly deaf can know what such silence means.

Without air our world would not be in darkness; for light does not, like sound, depend mainly upon air for its transmission. Light travels through regions where air is not; and if light is communicated by waves, they are not waves of air. But though the absence of air would not deprive the earth of light, it would make a very great difference in the kind and degree of light received.

Without air the blue sky would be black as ink; stars would glitter coldly in the daytime beside a glaring sun; deep shadows would alternate with blinding dazzle, and all the soft tints of sunrise and sunset would be wanting. Earth would be like the almost airless moon--all fierce whiteness and utter blackness--with no gray shades, no rosy gleams, no golden evening clouds; nay, without air there could be no clouds. On the moon is no twilight; for no air-particles float about, reflecting the sunlight from one to another, and forming a soft veil of brightness, to reach further than the direct sunlight alone can reach.

Sunbeams travel straight to earth, unbending as arrows in their flight, and unaided they can not creep any distance round a solid body, though they may be reflected or turned back from it. But the air breaks up the sunbeams, bends them, diffuses them, spreads them about, surrounds us with a delicate lacework of woven light. A sunbeam traveling through space is invisible till it strikes upon some object. If that object is solid, the light of the sunbeam is partly absorbed, partly reflected; if the object is transparent, the sunbeam passes through and onward. Few substances, if any, are perfectly transparent. We call air transparent, yet it is so only in a measure. Each sunbeam passing through the atmosphere loses part of its brightness by the way, and so the great glare of the sun is softened before it reaches the lower depths of the air-ocean.

The sun’s rays are rays of heat as well as of light. While the atmosphere softens the glare, giving us shade and twilight, it also modifies the extremes of temperature, from which, without air, we should suffer.

When the sun goes down, although we are often conscious of a chill, it is not the instant and overwhelming chill which we should feel but for the atmosphere. All day long the sun has been warming the earth and air. When his direct rays are withdrawn, the warm air for a while keeps its warmth, and gives over of that warmth to us.

WEATHER
--SIR RALPH ABERCROMBY

The earliest records of weather among every nation are to be found in those myths, or popular tales, which, while describing rain, cloud, wind, and other natural phenomena in highly figurative language, refer them to some supernatural or personal agency by way of explanation.

The most interesting thing about these mythical stories is the remarkable fidelity with which they reflect the climate of the country that gave them birth. For example, from the mythologies of Greece and Scandinavia we can almost construct an account of the climate of those two countries by simply translating the figurative phraseology of their legends into the language of modern meteorology.

Many survivals of mystic speech are still found among popular prognostics, and especially in cloud names.

In England and Sweden “Noah’s Ark” is still seen in the sky, while in Germany the “Sea-Ship” still turns its head to the wind before rain. In Scotland the “Wind-Dog” and the “Boar’s Head” are still the dread of the fisherman, while such names as “Goat’s Hair” and “Mare’s Tails” recall some of the shaggy monsters of antiquity.

At a rather later period of intellectual development, the premonitory signs of good or bad weather become formulated into short sayings, or popular prognostics. A large number of these are still current in every part of the world, but their quality and value are very varied. Some represent the astrological attitude of mind, by referring weather changes to the influence of the stars or phases of the moon; others, on the contrary, are very valuable, and, in conjunction with other aids to weather forecasting, prognostics will never be entirely superseded, especially for use on board ship. Till within a very recent period, their science and explanation had hardly advanced since they were first recorded. In many cases the prognostics came true; when they failed, no explanation could be suggested why they did so; neither could any reason be given why the same weather was not always preceded by the same signs. A halo sometimes precedes a storm; why does it not always do so? Why is rain sometimes preceded by a soft sky and sometimes by hard clouds?

About one hundred and fifty years ago the barometer was invented. Very soon after that discovery, observation showed that, in a general way, the mercury fell before rain and wind, and rose for finer weather. Also that bad weather was more common when the whole level of the barometer was low, independent of its motion one way or the other, than when the level was high. But as with prognostics, so with these indications, many failures occurred. Sometimes rain would fall with a high or rising barometer, and sometimes there would be a fine day with a very low or falling glass. No reason could be given for these apparent exceptions, and the whole science of barometric readings seemed to be shrouded in mystery.

The science of probabilities came into existence about the commencement of the Nineteenth Century, and developed the science of statistics. By this method the average readings of meteorological instruments, such as the height of the barometer or thermometer, or the mean direction and force of the wind, at any number of places were calculated, and the results were sometimes plotted on charts so as to show the distribution of mean pressure, temperature, etc., over the world.

By this means a great advance was made. Besides giving a numerical value to many abstract quantities, the plotting of such lines as the isothermals of Dove conclusively showed that many meteorological elements hitherto considered capricious were really controlled by general causes, such as the distribution of land and sea.

Still more fruitful were these charts as the parents of the more modern methods of plotting the readings of the barometer over large areas at a given moment, instead of the mean value for a month or year. Then by tabulating statistics the relative frequency of different winds at sea, many ocean voyages--notably those across the “doldrums,” or belt of calms near the equator--were materially shortened.

Statistics also of the annual amount of rainfall became of commercial value as bearing on questions of the economic supply of water for large towns, and much valuable information was acquired as to the dependence of mortality on different kinds of weather. Of more purely scientific interest were the variations of pressure, temperature, wind, etc., depending on the time of day, or what are technically known as diurnal variations, which were brought to light by these comparisons.

This branch of the subject is known as “Statistical Meteorology,” and has advanced very little since it was first developed by Dove and Kaemtz.

When the attempt was made to apply statistics to weather changes from day to day, it was found that average results were useless. The mean temperature for any particular day of the year might be 50°, if deduced from the returns of a great many years, but in any particular year it might be as low as 40°, or as high as 60°. The first application of the method was made by the great Napoleon, who requested Laplace to calculate when the cold set in severely over Russia. The latter found that on an average it did not set in hard till January. The emperor made his plans accordingly; a sharp spell of cold came in December, and the army was lost.

It has now been thoroughly recognized that statistics give a numerical representation of climate, but little or none of weather, and that large masses of figures have been accumulated, to which it is difficult to attach any physical significance. The misuse of statistics has done much to bring the science of meteorology into disrepute.

But within the last thirty years a new treatment of weather problems has been introduced, known as the synoptic method, by which the whole aspect of meteorology has been changed. By this method, a chart of a large area of the earth’s surface is taken, and after marking on the map the height of the barometer at each place, lines are drawn through all stations at which the barometer marks a particular height. Thus a line would be drawn through all places where the pressure was 30.0 inches, another through all where it was 29.8 inches, and so on at any intervals which were considered necessary. These lines are called “isobars,” because they mark out lines of equal pressure. When these charts were first introduced, the estimation of the value of the mean pressure was so great that, instead of drawing lines where pressure was equal at the moment, they were drawn through those places where the pressure was equally distant from the mean of the day for each place. These lines were called “is-abnormals”; that is, equal from the mean. After the isobars have been put in, lines are usually drawn through all places where the temperature is equal at the moment. These are called “isotherms,” or lines of equal temperature. Then arrows to mark the velocity and direction of the wind are inserted; and finally letters, or other symbols, to denote the appearance of the sky, the amount of cloud, or the occurrence of rain or snow. Such a chart is called a “synoptic chart,” because it enables the meteorologist to take a general view, as it were, over a large area. Sometimes they are called “synchronous charts,” because they are compiled from observations taken at the same moment of time.

1, Squall Cumulus; 2, Pillar Cumulus; 3, Cirrus; 4, High Stratus and Cumulus]

When these came to be examined, the following important generalizations were discovered:

1. That in general the configuration of the isobars assumed one of seven well-defined forms.

2. That, independent of the shape of the isobars, the wind always took a definite direction relative to the trend of those lines, and the position of the nearest area of low pressure.

3. That the velocity of the wind was always nearly proportional to the closeness of the isobars.

4. That the weather--that is to say, the kind of cloud, rain, fog, etc.--at any moment was related to the shape, and not the closeness, of the isobars, some shapes inclosing areas of fine, others of bad, weather.

5. That the regions thus mapped out by isobars were constantly shifting their position, so that changes of weather were caused by the drifting past of these areas of good or bad weather, just as on a small scale rain falls as a squall drives by. The motion of these areas was found to follow certain laws, so that forecasting weather changes in advance became possible.

6. That sometimes in the temperate zone, and habitually in the tropics, rain fell without any appreciable change in the isobars, though the wind conformed to the general law of these lines.

Observation also showed that, though the same shapes of isobars appear all over the world, the details of weather within them, and the nature of their motion, are modified by numerous local, diurnal, and annual variations. Hence modern weather science consists in working out for each country the details of the character and motion of the isobars which are usually found over it; just as the geologist finds crumplings and denudation all over the world, and works out the history of the physical appearance of his own scenery by studying the local development of these agencies.

So far the science rests on pure observation--that such and such wind or weather comes with such and such a shape of isobars. But it has been found, still further, that the seven fundamental shapes of isobars are, as it were, the product of so many various ways in which an atmosphere circulating from the equator to the poles may move. Just as the motion of a river sometimes forms descending eddies or whirlpools, sometimes back-waters in which the water is rising upward, or yet at other times ripples in which the circulation is very complex, so it now appears that the general movement of the atmosphere from the equator to the pole sometimes breaks up into a rotating and descending movement round that configuration of isobars known as an anticyclone, sometimes into a rotating and ascending movement round that known as a cyclone, or at other times quite in a different way during certain kinds of squalls and thunderstorms.

_Isobars, therefore, represent the effect on our barometers of the movements of the air above us, so that by means of isobars we trace the circulation and eddies of the atmosphere._

By carrying the general laws of physics into the conception of a circulating gas, we find that a cold mixed atmosphere of air and vapor descending into a warmer soil would remain clear and bright; while a similar atmosphere rising into cooler strata would condense some of its vapor into rain or cloud. It is by reasoning of this nature that the origin of some of the most beautiful and complex forms of clouds has been discovered.

Following out these lines of research, a new science of meteorology has grown up, which entirely alters the attitude of mind with which we regard weather changes, and gives rise to an entirely new method of weather forecasting that far surpasses all previous efforts, and which explains and develops all that was known before.

On the one hand, the new method not only explains why certain prognostics are usually signs of good or bad weather, and the reason why the indications sometimes fail; but also the reason why rain, for instance, is sometimes foretold by one prognostic and sometimes by a totally different one.

On the other hand, it not only gives a more extended meaning to all the statistics which partially represent the climate of a place, and to the relation of the diurnal to the general changes of weather; but it also enables new inferences to be drawn, which had hitherto been impossible from some observations, and explains why other sets of figures must always remain without any physical significance.

We may notice here an attempt which has been made by one school of meteorologists to deduce all weather _à priori_ from changes in the radiative energy of the sun; that is to say, that from a knowledge of greater or less heat being emitted by the sun, they would treat the consequent alteration of weather as a direct hydrodynamical problem. Given an earth surrounded by fifty miles of damp air, and a sun at varying altitude, and of varying radiative energy, deduce from that all the diverse changes of weather. This is doubtless a very tempting ideal, for there is no doubt that the sun’s heat is the prime mover of all atmospheric circulation; but when we have explained what the nature of weather changes is, we see that there is little hope that this method will ever lead to satisfactory results.

Other meteorologists, who lay less stress on the varying power of the sun, have taken up the indications of synoptic charts, and endeavored to construct a mathematical theory of cyclones and the general circulation of the atmosphere. Ferrel, Mohn, Gulberg, Sprung, and others have all started with the analysis of the motion of a free mass of air on the earth’s surface, first given by Professor Ferrel, and worked out, from that and other general principles, schemes of the nature and propagation of cyclones, and of the general distribution of pressure over the world.

THE ROMANCE OF A RAINDROP
--ARTHUR H. BELL

Depth of rainfall is, of course, ascertained by means of a rain-gauge, which measures the amount of water precipitated from the atmosphere during certain definite periods--usually twenty-four hours. Sir Christopher Wren has the credit of constructing the first rain-gauge; but they have been made in various shapes and sizes since his time; and perhaps none of the instruments in the meteorologist’s armory is so familiar to the general public as the rain-gauge. The methods of using the instrument and the meaning of rainfall statistics are also thoroughly understood nowadays. However, behind these statistics and the methods of obtaining them, there are questions of great interest that obtrude themselves when we are watching the falling rain, and we desire to learn about the history of the raindrop--for example: Why is a raindrop round? How are raindrops formed? At what particular time does vapor become visible as mist? And what are the causes which change this mist into cloud and subsequently into rain?

The two prime causes of rain are, of course, the sun and the ocean; and since these two factors do not appreciably vary from year to year, it follows that the annual rainfall on the earth as a whole, if it could be measured, would also be found to be invariable. It is obvious, however, that the rainfall at all places is not equal. In London, for instance, the average yearly rainfall is twenty-two inches; but on the Khasi Hills in India it is no less than six hundred inches. Similar contrasts are observable in other parts of the world, the differences being due to local geographical conditions.