The Ocean and its Wonders, Robert Michael Ballantyne [portable ebook reader txt] 📗

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 other as to give the impression of perpetual flashes and an unintermitting roar; the whole scene presenting an aspect so awful, that sinful man might well suppose the season of the Earth's probation had passed away, and that the Almighty were about to hurl complete destruction upon his offending creatures.

But far other intentions are in the breast of Him who rides upon the storm. His object is to restore, not to destroy--to gladden, not to terrify. This tempestuous weather lasts for some days, but at the end of that time the change that comes over the face of nature seems little short of miraculous. In the words of Mr Elphinstone, who describes from personal observation--"The whole earth is covered with a sudden but luxuriant verdure, the rivers are full and tranquil, the air is pure and delicious, and the sky is varied and embellished with clouds.

"The effect of this change is visible on all the animal creation, and can only be imagined in Europe by supposing the depth of a dreary winter to start at once into all the freshness and brilliancy of spring. From that time the rain falls at intervals for about a month, when it comes on again with great violence; and in July the rains are at their height. During the third month they rather diminish, but are still heavy. In September they gradually abate, and are often suspended till near the end of the month, when they depart amid thunders and tempests, as they came."

Such are the effects of the monsoons upon land and sea. Of course the terrific gales that usher them in and out could not be expected to pass without doing a good deal of damage, especially to shipping. But this is more than compensated by the facilities which they afford to navigation.

In many parts of the world, especially in the Indian Ocean, merchants calculate with certainty on these periodical winds. They despatch their ships with, say, the north-east monsoon, transact business in distant lands, and receive them back, laden with foreign produce, by the south-west monsoon. If there were no monsoons, the voyage from Canton to England could not be accomplished in nearly so short a time as it is at present.

And now as to the cause of monsoons. They are, for the most part, _deflected trade-winds_. And they owe their deflection to the presence of large continents. If there were no land near the equator, the trade-winds would always blow in the same manner right round the world; but the great continents, with their intensely-heated surfaces, cause local disturbance of the trade-winds. When a trade-wind is turned out of its course, it is regarded as a monsoon. For instance, the summer sun, beating on the interior plains of Asia, creates such intense heat in the atmosphere that it is more than sufficient to neutralise the forces which cause the trade-winds to blow. They are, accordingly, arrested and turned back. The great general law of the trades is in this region temporarily suspended, and the monsoons are created.

It is thus that the heated plains of Africa and Central America produce the monsoons of the Atlantic, the Pacific, and the Gulf of Mexico.

We think it unnecessary to explain minutely the causes that produce variation in the monsoons. Every intelligent reader will readily conceive how the change of seasons and varied configuration as well as unequal arrangement of land and water, will reverse, alter, and modify the direction and strength of the monsoons.

Land and sea breezes are the next species of wind to which we would direct attention. They occur in tropical countries, and owe their existence to the fact that the land is much more easily affected by sudden changes of temperature than the sea. Thus, the land in warm regions is much heated by the sun's rays during the day; the atmosphere over it becomes also heated, in virtue of which it rises: the cool atmosphere over the sea rushes in to supply its place, and forms the _sea breeze_: which occurs only during the day.

At night the converse of this takes place. Land heats and cools rapidly; water heats and cools slowly. After the sun sets, the cooling of the land goes on faster than that of the sea. In a short time the atmosphere over the land becomes cooler than that over the sea; it descends and flows off out to sea; thus forming the _land breeze_. It occurs only at night, and when the change from one to the other is taking place there is always a short period of calm. Land and sea breezes are of the greatest use in refreshing those regions which, without them, would be almost, if not altogether, uninhabitable.

In "The Tempest," an interesting work on the origin and phenomena of wind, published by the Society for Promoting Christian Knowledge, a curious and simple experiment is described, whereby the existence of upper and under currents of air and the action of land and sea breezes may be clearly seen and understood. We quote the passage:--

"The existence of the upper and under currents of air which mark the phenomena of the trade-winds, and of land and sea breezes, may be beautifully illustrated in two adjoining rooms, in one of which a good fire is burning, while in the other there is none. If the door between the two rooms be thrown open, the cold air will enter the heated room in a strong current, or, in other words, as a violent wind. At the same time the heated air of the warm room ascends and passes the contrary way into the cold room, at the upper part of the same doorway; while in the middle of this opening, exactly between the two currents, the air appears to have little or no motion. The best way to show this experiment is to introduce the flame of a candle into the doorway between a hot and a cold room. If the flame be held near the bottom of the doorway, where the air is most dense, it will be strongly drawn towards the heated room; and if held near the top of the door it will be drawn towards the cold room with somewhat less force; while midway between the top and bottom the flame will be scarcely disturbed.

"There is also another pretty experiment which illustrates well the theory of land and sea breezes. Take a large dish, fill it with cold water, and in the middle of this put a water-plate or a saucer filled with warm water. The first will represent the ocean, and the latter an island made hot by the rays of the sun, and rarefying the air above it. Take a lighted wax candle and blow it out; and, if the air of the room be still, on applying it successively to every side of the saucer, the smoke will be seen moving towards the saucer and rising over it, thus indicating the course of the air from sea to land. On reversing the experiment, by filling the saucer with cold water (to represent the island at night) and the dish with warm water, the land breeze will be shown by holding the smoking wick over the edge of the saucer; the smoke will then be wafted to the warmer air over the dish."

We have just tried the first of these experiments, with complete success. We would, however, recommend a piece of twisted brown paper, lighted and blown out, instead of a wax candle, because