We know, of course, how we can produce hot air in any given room—by the simple expedient of lighting a fire. Among the planets the sun is the stove and the planets are the rooms which are to be heated. Now a stove causes a considerable commotion in the air—a circular commotion. The hot air will rise towards the ceiling. As soon as it gets there it will be further removed from the original source of heat than it was before, and as a result it will begin to cool off The cooling process will cause it to lose its lightness and to fall back towards the earth. But as soon as it gets a little lower it will once more get in touch with the stove. Once more it will grow warmer and lighter and once more it will begin to rise. And so on and so forth, until the stove goes out. But then the walls of the room, which have absorbed considerable heat while the stove was burning, will keep the room warm for a shorter or longer time, depending upon the material of which they are made.
These walls may be compared to the soil on which we happen to live. Sand and rocks absorb heat quicker than a rain-soaked marsh, but by the same token they let go of it with much greater case. As a result, the desert is uncomfortably cold a short time after the setting of the sun, while a forest remains warm and comfortable for hours after the entrance of darkness.
Water is a veritable reservoir for the storing up of heat. As a result all countries situated on or near the ocean enjoy a much more even temperature than those set in the heart of a continent.
HEAT
If you have tried to make the bathroom a little less shivery on an extra cold day with a small electric heater, you will know that much depends upon the angle at which that little stove is placed. The same holds true for the sun. In the tropics the rays of the sun hit the surface of the earth much more directly than near the poles. Rays of sunlight, therefore, a hundred miles wide, landing fairly and squarely upon a hundred miles of African forest or South American wilderness, will be able to devote their entire strength to these hundred miles of territory and to nothing else. But near the poles rays of sunlight a hundred miles wide will Cover a stretch of land or ice that is twice as wide (as the picture will show you much more easily than a thousand words could hope to do), and the heating power of those hundred miles of sunlight near the poles will therefore be halved, just as an oil-burner which is supposed to keep a six-room flat at a comfortable temperature will prove a failure when called upon to perform a similar service for a twelve-room flat.
THE SUN HEATING THE EARTH
On their way to our planet the sunrays pass through the atmosphere, but they pass through so easily and quickly that they hardly influence the temperature of that faithful terrestrial blanket. Then they hit the earth, and the earth stores up the heat and slowly surrenders part of it to the atmosphere. That fact, incidentally, explains why it is so cold on the top of a mountain. For the higher we get, the less the heat of the earth has been able to make itself felt. If the sun heated the atmosphere directly and the atmosphere in its turn heated the earth, it would be just the other way round and our mountain tops would not be covered with snow.
RAIN
And now we come to the most difficult part of the problem. Air is not just ‘air’ in our sense of the word. It has both substance and weight. The lower layers of air, therefore, are under a much higher pressure than the higher ones. When you want to flatten out a leaf or a flower you put it between the pages of a book and then put twenty other volumes on top of it because you know that the pressure will be greatest in the book that is at the bottom of the pile. The pressure under which we human beings live is considerably more than most of us suspect. It is fifteen pounds per square inch. That means that we would be crushed flat except for the fortunate circumstance that we are filled with the same air as that which surrounds us. Even so, 30,000 pounds (the pressure upon a body of average size) is a respectable amount. If you have any doubts upon the subject, try to lift a small goods wagon.
Within the realm of the atmosphere itself, however, that pressure is constantly changing. We know this through an invention of Evangelista Torricelli, a pupil of Galileo, who about the middle of the seventeenth century gave us the barometer, that well-known instrument by which we are able to measure the pressure of the air at any time of day or night.
As soon as these Torricellian tubes had been placed upon the market, people began to experiment with them. They noticed that the pressure fell by about an inch for every 900 feet one ascended above sea-level. Then followed another discovery which did much to make meteorology, the study of atmospheric phenomena, a reliable science in forecasting the weather.
Certain physicists and geographers began to suspect that there was a definite connexion between the pressure of the air and the direction of the prevailing winds, or vice versa. But, in order to establish some irrefutable law regulating the behaviour of all air-currents, it was first necessary to spend several centuries collecting the data from which to draw a few definite conclusions. When this had been done it was shown that certain parts of the world enjoyed an air pressure well above that of the mean sea-level, while others had pressures far below that at mean sea-level. The first of these were then called high-pressure areas and the second low-pressure areas. Next it was definitely established that winds would always tend to blow from high-pressure areas to low-pressure areas and that the velocity and strength of the wind would depend upon the highness of the high-pressure area and the lowness of the low-pressure area. And when the high-pressure Was very high and the low-pressure was very low, then we would have a very violent wind—a storm, a cyclone, or a hurricane.
RAINSTORMS ARE ONLY LOCAL AFFAIRS
The winds not only keep our living quarters, the earth, decently Ventilated, but they also play a great part in the distribution of that fain without which a normal development of plant life and animal life would be completely impossible.
Rain is merely evaporated water from the oceans and from the Inland seas and from the inland snow-fields, which is carried along by the air in the form of vapour. As hot air can hold much more vapour than cold air, the water-vapour will be carried along without much difficulty until the air grows colder. Then part of it is condensed and falls back upon the surface of the earth in the form of rain or hail or snow.
The rainfall of any given region therefore will depend almost entirely upon the winds to which it is exposed. If we have a sea-coast separated from the mainland by mountains (a very common occurrence) and the winds blow from the sea, the coastal region will be wet and damp. For the wind, being forced to rise into higher regions (where the pressure is lower), will cool off as it gets further and further away from the sea-level and it will shed its vapour in the form of rain and snow and will reappear on the other side of the mountain range as a dry wind.
The rainfall of the tropics is both regular and abundant because the enormous heat of the land makes the air rise to a great height, where it gets cooled off and is obliged to release most of its vapour, which thereupon returns to earth in the form of heavy sheets of rain. But as the sun is not always right over the equator, but moves to the north and south of it, most of the equatorial regions have two seasons during which there are terrific rainstorms and two seasons relatively dry.
But those regions which are exposed to steady air-currents flowing from colder to warmer regions are by far the worst off For as the winds pass from the cold area to the hot one, their capacity for absorption becomes steadily greater, and therefore they do not release the vapour they carry, causing many parts of this earth to be turned into deserts where it may not rain more than once or twice every ten years.
So much for the general subject of wind and rain. A detailed discussion will follow when we describe each individual country.
And now a few words about the earth itself, and about that thin crust of hardened rock on which we live.
There are a great many theories about the nature of the interior of our planet, but our definite knowledge upon the subject is still exceedingly vague.
Let us be honest. How high h
ave we ever been up in the air or how low down into the bowels of the earth?
On a globe of three feet in diameter, the highest mountain in the world, Mt Everest, would appear about as thick as a thin piece of tissue paper, and the deepest hole in the ocean, just east of the Philippine Islands, would be represented by a dent of the size and shape of a postage stamp. Well, we have never yet descended to the utmost depths of the ocean and we have never yet climbed Everest. We have been a little higher than the top of this Himalayan giant in balloons and flying machines, but when all is said and done, even after the successful flights of the Swiss Professor Piccard and others, 29/30 of the atmosphere still remain to be explored. As for the water, we have never yet descended below 1/40 of the total depth of the Pacific Ocean, and, incidentally, the depth of the deepest sea is greater than the height of the highest mountain. If we dumped Everest into the deepest part of the ocean its top would be several thousand feet below the surface of the sea.
In the light of our present-day knowledge, however, these facts prove nothing at all about the origin and the subsequent development of the crust of the earth. Neither (as our grandfathers so fondly hoped) can we turn to our volcanoes for information about the true inner nature of our planet, for we have come to realize that those are not outlets for the hot substance that is supposed to fill the interior of the earth.
In round numbers there are still some 320 active volcanoes left. There used to be 400 others on the active list, but these have since been retired and pensioned off with the rank of ordinary or common mountains.
The great majority of these volcanoes are situated near the sea-coast. Indeed, the most restless part of the world’s crust, Japan (where the seismograph shows a slight volcanic disturbance four times every day, or 1447 times a year), is a group of islands, and Krakatoa and Martinique, the most tragic victims of recent volcanic outbursts, were islands also.
In view of the close proximity of sea to volcano, it was quite natural that people should have tried to explain all volcanic eruptions as the result of water seeping into the inner part of the earth, thereby causing a sort of gigantic boiler explosion with the well-known disastrous results of an overflow of lava and steam. But since then we have discovered several very busy volcanoes hundreds of miles away from the sea, and that theory, too, has therefore come to nought. Ask me again about all this two centuries hence; at the present moment we can only shake our heads and repeat: “We do not know.”
THE CRUST OF THE EARTH IS AS FULL OF HOLES AS A SPONGE
Meanwhile, what about the surface of the earth itself? We used to talk so glibly about the rock of ages that would for ever defy the changes of time. Modern science is less confident and regards this rock and all other rocks as something living and therefore subject to constant change. The rain raineth upon it and the wind bloweth upon it, and together, with the help of Jack Frost and his glaciers, they cause the mountains to wither away at the rate of three inches every ten centuries. If there were no counter-moves to offset these erosive attacks, the older mountains would have disappeared long ago; even the Himalayas would have been turned into a vast plain in about 116,000,000 years. But there are counter-activities and plenty of them.
WHY NOT MAKE YOUR OWN EARTHQUAKE?
In order to get at least a vague idea of what is really happening all around us, take half a dozen clean handkerchiefs and spread them out flat on the table, one on top of one other. Then push all six together by moving your hands very slowly towards each other. You will get a pile of curiously wrinkled linen with mountains and valleys and folds and counter-folds all over it, and that pile of curiously wrinkled linen will bear a very close resemblance to the crust of the earth. That crust is part of an enormous structure racing through space and constantly losing some of its heat. Like all things that are coding off, it is slowly contracting. As you probably know, when an object contracts the outer surface will get curiously rumpled and creased, like a couple of handkerchiefs being pushed together.
THE RISE AND FALL OF ALL MOUNTAINS
The best guess at the present moment (but remember that it is only a guess) tells us that the diameter of the earth has shrunk some thirty miles since the beginning of our independent existence as a planet. That does not seem very much when you think of it as a straight line. But remember the tremendous scope of the curved planes with which we are dealing. The surface of the world is 196,550,000 square miles. A sudden change of only a few yards in diameter would be enough to cause a catastrophe which none of us would survive.
Nature therefore works very slowly her wonders to perform. She insists upon maintaining a proper balance in everything she does. When she allows one expanse of water to run dry (Great Salt Lake, Utah, is rapidly dwindling away, the Lake of Constance in Switzerland will be gone in another 100,000 years) she starts another in some other part of the world; and when she permits certain mountain-ranges to disappear (the Alps in Central Europe will be as flat as the American prairies in another 60,000,000 years) then another part of the crust in a totally different corner of the globe is slowly being reshaped and wrinkled into a fresh mountain-range. That, at least, we believe to be the case, although as a rule the process is far too slow and gradual to allow us to make any concrete observations of the changes that are taking place.
THE GLACIERS IN AMERICA
There is, however, an exception to this general rule. When left to herself, Nature is in no particular hurry. But when aided and abetted by man, she sometimes proves herself an uncomfortably fast worker. And ever since man became truly civilized and invented his little steam-engines and his little sticks of dynamite, the surface of the earth has been transformed so rapidly that our great-grandparents would hardly recognize their own pastures and gardens, were they to come back to us for a little holiday. Our greed for timber and the ruthlessness with which we have denuded whole mountain-ranges of their blanket of forests and shrubs have turned vast regions into primeval wildernesses. For as soon as the forests were gone, that fertile soil which for so many years had faithfully clung to the rocky surface of the hill-sides was brutally washed away and the barren slopes became a menace to the surrounding country-side. The rain was then no longer held captive by the turf and by the roots of the trees, but was able to rush down in torrents and cataracts, destroying everything it met on its way towards the valleys and plains.
THE GLACIERS IN EUROPE
And this unfortunately is not said in a flight of high rhetorical exaggeration. We don’t have to go back to the glacial periods when, for reasons as yet unexplained, the whole of northern Europe and northern America lay buried beneath a heavy blanket of ice and snow which dug such dangerous grooves through entire mountain ranges. We need only go as far back as the era of the Romans, who were first-rate exploiters (weren’t they the ‘practical men’ of antiquity?) and who in less than five generations completely changed the climate of their own peninsula by the senseless destruction of everything that had thus far helped to make Italy a country of well-balanced and even temperature. And what the Spaniards did to the mountains of South America, when they allowed the fertile terraces, built by countless generations of patient little Indians, to go to ruin, is a fact of such recent Occurrence as to need no further elucidation.
Of course that was the easiest way to deprive the natives of their livelihood and reduce them to obedience by way of starvation just as the extinction of the buffaloes by the United States Government was the most practical method of turning fierce warriors into dirty, slovenly reservation-parishioners. But these cruel and senseless measures carried their own punishment with them, as any one familiar with the North American plains or the Andes will tell you.
Fortunately this is among the few problems of practical geographical importance which have at last penetrated to the consciousness of those who sit in the seats of the mighty. No Government to-day would any longer tolerate such scandalous interference with the soil upon which we all depend for our well-being. We have no control over the cosmic chang
es which take place in the crust of our planet. But to a certain extent we can control a vast number of details which make for a greater or smaller rainfall in any given territory and which will prevent fertile regions from being turned into howling deserts. We may not know anything about the inside of this earth, but we have at least learned a great many things about the outside. And every day we add to the sum total of this useful knowledge and use it wisely for the benefit of all.
But I regret to say that we have no such control over the greater part of the earth’s surface—that part which, we call the oceans and the seas. Almost three-quarters of our globe are uninhabitable because they are covered by a layer of water, differing in depth from a couple of feet (near the shore) to over 35,000 feet in the famous ‘deep’ just east of the Philippines.
This layer of water can be roughly divided into three main parts. The most important of these is the Pacific Ocean, which covers 64,000,000 square miles. The Atlantic Ocean covers 31,500,000 square miles, and the Indian Ocean 29,000,000. Inland seas account for another 2,000,000 square miles, while lakes and rivers take up about 1,000,000 square miles of their own. All this submerged territory was and is lost to us as a place of residence, unless we are able to re-develop those gills which our ancestors of a few million years ago possessed and of which we still show the traces on the day of our birth.
This abundant supply of water may at first seem a complete waste of perfectly good territory and it may make us regret that our planet is as wet as it happens to be. For when we remember that 5,000,000 square miles of the land that is at our disposal are desert and that 19,000,000 square miles are steppes or plains of the semi-useless Siberian variety, while a considerable number of other millions of square miles are uninhabitable because they are either too high for us to live in (like the Himalayas and the Alps) or too cold (like the territory around the North and South Poles) or too wet (like the swamps of South America) or too densely covered with forests (like the forests of central Africa) and must therefore be deducted from the 55,510,000 square miles that are described as ‘land,’ we feel that we could make excellent use of a few more miles of added territory.
The Home of Mankind Page 3
