The Ocean and Its Wonders by R. M. Ballantyne (ebook reader with built in dictionary txt) đź“•
Read free book «The Ocean and Its Wonders by R. M. Ballantyne (ebook reader with built in dictionary txt) 📕» - read online or download for free at americanlibrarybooks.com
- Author: R. M. Ballantyne
Read book online «The Ocean and Its Wonders by R. M. Ballantyne (ebook reader with built in dictionary txt) 📕». Author - R. M. Ballantyne
May we not here remark, that this evil was owing to another evil—namely, man’s ignorance of, or indifference to, the duty of what we may term human communication? As surely as gravitation is an appointed law of God, so surely is it an appointed duty that men shall communicate their individual knowledge to each other, in order that the general knowledge of the species may advance and just in proportion to the fidelity with which men obey this duty—the care and ability with which they collate and systematise and investigate their knowledge—will be the result of their efforts.
In order to make the above remarks more clear as regards atmospheric phenomena, let us suppose the case of a sailor who makes the same voyage every year, but not precisely at the same time each year (and it must be remembered that the rigid punctuality at starting which now holds good did not exist in former times). In his first voyage he had to cross, say, four of the wind-belts. While crossing belt number one, he experiences south-west winds chiefly, and, being an observant man, notes the fact. In belt number two he encounters westerly winds. In number three he is in a region of variable winds and calms. In this region the winds blow all round the compass, averaging about three months from each quarter. But our sailor does not know that; he does not stay there all the year to make notes; he passes on, having recorded his experience. In crossing belt number four, he finds the prevailing winds to be easterly.
Next year he sets forth again but merchants are not always punctual. The lading cannot be completed in time, or adverse winds render the setting sail unadvisable. At length, after a month or six weeks’ delay, he proceeds on his voyage, and finds belt number one perhaps much the same as last year. He congratulates himself on his good fortune, and notes his observations; but in belt number two, the wind is somewhat modified, owing to its being later in the season,—it is rather against him. In number three it is right in his teeth, whereas last year it was quite in his favour. In number four, which we will suppose is the trade-wind belt (of which more hereafter), he finds the wind still easterly. Here, then, is the groundwork of confusion in our sailor’s mind. He has not the remotest idea that in belt number one the wind blows chiefly, but not always, in one particular direction; that in number four it blows invariably in one way; and that in number three it is regularly irregular. In fact, he does not know that such belts exist at all, and his opportunities of observing are not sufficiently frequent or prolonged to enable him to ascertain anything with certainty.
Now, when we remember that in this imperfect experience of his he is still further misled by his frequently encountering local vicissitudes—such as storms and calms resulting from local and temporary causes—we see how confusion becomes worse confounded. No doubt he does gather some few crumbs of knowledge; but he is called on, perhaps, to change his scene of action. Another ship is given to him, another route entered on, and he ceases altogether to prosecute his inquiries in the old region. Or old age comes on; and even although he may have been beginning to have a few faint glimmerings as to laws and systems in his mind, he has not the power to make much of these. He dies; his knowledge is, to a very large extent, lost, and his log-books disappear, as all such books do, nobody knows or cares where.
Now this state of things has been changing during the last few years. Log-books are collected in thousands. The experiences of many men, in reference to the same spots in the same years, months, and even hours, are gathered, collated, and compared; and the result is, that although there are conflicting elements and contradictory appearances, order has been discovered in the midst of apparent confusion, and scientific men have been enabled to pierce through the chaos of littlenesses by which the world’s vision has been hitherto obscured, and to lay bare many of those grand progressions of nature which move unvaryingly with stately step through space and time, as the river, with all its minor eddies and counter-currents, flows with unvarying regularity to the ocean.
Before proceeding to speak of the power and the dreadful effects of wind, it is necessary to say a word or two about the trade-winds.
It is supposed that the “trades” derived their name from the fact of their being favourable to navigation, and, therefore, to trade. They consist of two belts of wind, one on each side of the equator, which blow always in the same direction.
In the last chapter it was explained that the heated atmosphere at the equator rises, and that the cooler atmosphere from the poles rushes in to supply its place. That which rushes from the south pole is, of course, a south wind, that from the north pole a north wind; but, owing to the Earth’s motion on its axis from west to east, the one becomes a north-east, the other a south-east wind. These are the north-east and the South-east “trades.” They blow regularly—sometimes gently, sometimes fiercely—all the year round. Between the two is a belt of calms and changeable breezes, varying from 150 to 500 miles broad—according to the time of the year—where there are frequent and violent squalls, of very short duration, accompanied with heavy rains. This region is called by seamen the “doldrums,” and considerable trouble and difficulty do ships experience in crossing it.
It has already been explained that about latitude 30 degrees, the upper current of wind from the south descends. At the same point the upper current from the north also descends. They cut through each other, and the point where these two cut each other is the northern limit of the north-east trade-winds. The same explanation holds in regard to the southern limit of the south-east trades.
In the accompanying diagram the arrows within the circle point out the direction of the north-east and the south-east “trades” between the tropics of cancer and capricorn, and also the counter currents to the north and south of these, while the arrows around the circle show how counter currents meet and rise, or descend, and produce the calm belts.
We have hitherto enlarged chiefly on the grand currents of the atmosphere, and on those modifying causes and effects which are perpetual. Let us now turn to the consideration of those winds which are produced by local causes, and the effects of which are partial.
And here we are induced to revert to the Gulf Stream, which has been already referred to as a local disturber of the regular flow of the atmosphere. This immense body of heated water, passing through cold regions of the sea, has the effect of causing the most violent storms. The hurricanes of the West Indies are among the most violent in the world. We have read of one so violent that it “forced the Gulf Stream back to its sources, and piled up the water in the Gulf to the height of thirty feet. A vessel named the Ledbnry Snow attempted to ride it out. When it abated, she found herself high up on the dry land, having let go her anchor among the tree-tops of Elliott’s quay! The Florida quays were inundated many feet; and it is said the scene presented in the Gulf Stream was never surpassed in awful sublimity on the ocean. The water thus dammed up rushed out with frightful velocity against the fury of the gale, producing a sea that beggared description.”
The monsoons of the Indian Ocean are among the most striking and regular of the locally-caused winds. Before touching on their causes, let us glance at their effects. They blow for nearly six months in one direction, and for the other six in the opposite direction. At the period of their changing, terrific gales are frequent—gales such as we, in our temperate regions, never dream of.
What is termed the rainy season in India is the result of the south-west monsoon, which for four months in the year deluges the regions within its influence with rain.
The commencement of the south-west monsoon is described as being sublime and awful beyond description. Before it comes, the whole country is pining under the influence of long-continued drought and heat; the ground is parched and rent; scarcely a blade of verdure is to be seen except in the beds of rivers, where the last pools of water seem about to evaporate, and leave the land under the dominion of perpetual sterility. Man and beast pant for fresh air and cool water; but no cool breeze comes. A blast, as if from the mouth of a furnace, greets the burning cheek; no blessed drops descend; the sky is clear as a mirror, without a single cloud to mitigate the intensity of the sun’s withering rays. At last, on some happy morning, small clouds are seen on the horizon. They may be no bigger than a man’s hand, but they are blessed harbingers of rain. To those who know not what is coming, there seems at first no improvement on the previous sultry calms. There is a sense of suffocating heat in the atmosphere; a thin haze creeps over the sky, but it scarcely affects the broad glare of the sun.
At length the sky begins to change. The horizon becomes black. Great masses of dark clouds rise out of the sea. Fitful gusts of wind begin to blow, and as suddenly to cease; and these signs of coming tempest keep dallying with each other, as if to tantalise the expectant creation. The lower part of the sky becomes deep red, the gathering clouds spread over the heavens, and a deep gloom is cast upon the earth and sea.
And now the storm breaks forth. The violent gusts swell into a continuous, furious gale. Rain falls, not in drops, but in broad sheets. The black sea is crested with white foam, which is quickly swept up and mingled with the waters above; while those below heave up their billows, and rage and roar in unison with the tempest. On the land everything seems about to be uprooted and hurled to destruction. The tall straight cocoa-nut trees are bent over till they almost lie along the ground; the sand and dry earth are whirled up in eddying clouds, and everything movable is torn up and swept away.
To add to the dire uproar, thunder now peals from the skies in loud, continuous roars, and in sharp angry crashes, while lightning plays about in broad sheets all over the sky, the one following so close on the
Comments (0)