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Monsoons. Our terraqueous globe is wrapped in a layer of air about forty miles high. This air is chiefly a mechanical mixture of nitrogen and oxygen gas, but is also the recipient of all the volatile matters which rise from the surface of the globe, and, among others, of the vapour of water in proportionally large quantity. The heat of the sun draws up the watery vapour from the seas and rivers, and so long as it is in the state of vapour it remains invisible; but on cooling it again takes palpable form, and falls to the earth from which it rose. It may be condensed and precipitated either by the greater cold of the higher spaces of the atmosphere into which it has ascended, or through being traversed by a colder current of air, or from its being whirled, with the revolving globe, away from the heat of the sun into the earth's cool shadow, which we call the night. The cold of a clear night precipitates it as dew, or hoarfrost, which is frozen dew. A fog is caused by the condensation of the watery vapour in the air that rests directly on cold ground. A cloud is a fog high in air, and snow is a frozen cloud, which, as it congeals, descends. Rain is caused by the gathering together of many clouds, or aerial fogs. The sun cannot dissipate them, and their moisture gradually collects in drops, which fall as rain. Hail is a shower of rain, suddenly frozen as it falls. The heat of the sun also sets the atmosphere in motion, the winds which blow over the face of the earth being caused by the unequal heating of the air. When a fire is lighted the air it heats ascends the chimney, carrying the smoke with it, and the vacuum caused in the air of the room draws to the bearth the colder outside air through every opening in the doors and windows; and when a city is on fire, so great is the vacuum caused by the upward draught of heated air, that the cooler surrounding air flows in to take its place as a violent wind; and so in accounts of great conflagratious we often read that the terror of the inhabitants was increased by the hurricane which blew at the same time. In such a fire it will be observed that the column of smoke from it does not go up for ever, but as it rises into the cooler air it spreads out on all sides like the branches of a palm, and gradually falls in “blacks” to the earth; and in this way bits of charred wood and paper are often brought back again to a fire by the wind caused by it. Within the tropics the sun's rays fall vertically on the air, and its heated particles, constantly rising, form a column ever moving towards the poles. To fill the vacuum thus caused, colder air from the frozen poles rashes down over the surface of the globe towards the equator, and hence result the great polar and equatorial air currents, the direct courses of which between the poles and the equator are bent by the revolution of the earth on its axis, in the northern hemisphere into the North-East and in the southern hemisphere into the SouthEast “ trade winds" or vents alisées ; which are called “ trade winds," not because they facilitato commerce, but because they hold a certain steady course, or tread, all round the earth. The air brought by the “trade winds" ascends to a great height in the tropics and flows back towards the poles, in the northern hemisphere as the South East " antitrade," and in the southern as the North-East “anti-trade.” The ascending air carries with it an immeuse volume of watery vapour, and
as the air is quite calm on or near the equator, where the trade winds meet, this vapour, as soon as it reaches the upper atmosphere, is at once precipitated in the rains which fall within the tropics nearly all round the year. It is now proved that the Assyrians three thousand years ago had anticipated Dr. Hunter's theory of the periodicity of sun-spots, which implies, that they also understood the theory of climate, as expressed in Ecclesiastes, i. 6:4" The wind goeth toward the south, and tarneth about unto the north; it whirleth about continually, and the wind returneth again according to his circuits.” Had the world remained, as it probably once was, a waste of waters, the trade winds would have blown over it, and all round the year, uninterraptedly, and the moisture in the air would have fallen on the earth in three continuous belts, one corresponding with the equator, and the others with the calms of Cancer and Capricorn; these calms would indeed have reached to the poles, and darkness covered the face of the deep. But the globe is divided between sea and land, and the land becomes hotter more quickly than the sea, as shown by the “sea breeze," which begins to blow. about noonday in the tropics, and cools more quickly, as shown by the dangerous “land wind," which in tropical countries begins about midnight to blow over the land toward the sea; and the consequence is that when the son becomes vertical over any portion of the earth's land surface, it draws the surrounding air to a focus there; and in this way, in every latitude, the great primary winds and rains are broken into secondary, or local winds and rains, producing the differences in nature and seasons of the climates which prevail over the globe. Thus the manifold climates of the world are caused by the inutual relations of its atmosphere and sea and land; and all the changes of weather, shade and sunshine, heat and cold, calm and tempest, drought and rain, depend upon the movements into which the atmosphere is thrown by the sun.
Owing to the excess of land in the northern hemispbere, the constant belt of rain where it exists between the trade winds, instead of corresponding with the equator, lies a little to its north, and the moisture gathered by the South-East trades only falls in rain when it reaches the tropic of Cancer, thus compensating the northern hemisphere for its want of evaporating (sea) surface. Similar modifications and compensations, on a smaller scale, occur in regard to each of the trades separately as the sun successively passes through the North and South ecliptic. But here we have only to consider “ The Rains,” or “ SouthWest Monsoon ” of Western India. India stretches out into the belt of the North-East trades, and were there undeviating winds the only rain wbich this immense peninsula would receive would be tbat which falls from October to April during the North-East “Monsoon.” The rain which then falls is not brought by this wind, for as it blows from the high lands of Eastern Asia, it bears with it but little watery vapour, except what it may lap up in the Bay of Bengal. But the great volume of rain which falls on India during the North-East Monsoon, or Winter Rains, is really derived from the evaporation of the ocean about Australia, wbere during our winter months the sun is shining with all the force of midsummer. The vapour there drawn up into the bigher atmosphere returns in an upper current towards India, where it is precipitated through the lower current blowing from the North-East, and furnishes the North-East Monsoon rains, on which the Indian winter crops depend. If India depended on the North-East Monsoon rains alone, it would indeed be almost as unfortunately circumstanced as the peninsula of Arabia, wedged in between the high lands of Persia and Abyssinia. But observe what actually takes place. At the vernal equinox, March 21, the sun passes from the southern hemisphere to the northern; is first vertical over Bombay about May 15; reaches the highest point of his upward journey, or summer solstice, June 21 ; descending is again vertical over Bombay about July 27; and finally, at the autumnal equinox, September 23, having traversed the whole tropic of Cancer, re-enters the tropic of Capricorn, reaching its lowest southern point, or winter solstice, December 22. Between May and July he shines down furiously on the sandy plains of Scinde and Rajputana, and the great grassy plains of Central Asia, from which so vast a column of heated air ascends up through the atmosphere that the draught caused has the power not only to completely reverse the normal direction of the North-East trade, but even to deflect and draw the South-East trade toward India. Thus is the South-West Monsoon of India brought about. This mighty wind, laden with the moisture gathered from the Indian Ocean, strikes the Malabar Coast and Concans at nearly right angles, and there, chilled by the cool green forest barrier of the Ghâts, pours down its condensed vapours on Western India for four months in violent rains, which are ushered in and depart with the most violent thunderstorms; and thus it is also that the temperature of India is lowered during months that otherwise would be so hot as to make the country unendurable. The Deccan slopes eastward, having been upheaved chiefly by the eruption of the Western Gbâts, and the superfluous rain which falls on them, that does not flow off in the mountain torrents of the Concans, slowly drains off to the Bay of Bengal in such continental rivers as the Godavery, Cauvery, Pennair, and Kistna. But the Gbâts do not line the whole coast; they cease about Surat; and there the Santpura and Vindya mountains condense the clouds borne by the South-West Monsoods, which are poured into the Arabian Sea by the Tapti and Nerbudda, the only Deccan rivers flowing westward; while from the Arrivali hills in Rajputana, the Sabermatti flows through the fertile plains of Gujerat. The South. West Monsoon reaches to the wide plain of Hindostan, the Punjab, and Scinde; and all round the coasts of India and Southern Asia, within the influence of the great solstitial up-draught from the deserts of Rajputana and Central Asia, we find the phenomenon of summer rains. At the very time, also, that the sun is drawing the vapours of the Indian Ocean towards the Western Ghâts his rays are melting the snows of the Himalaya and Hindu Kush, which flow down to the Arabian Sea and Bay of Bengal in the perennial streams of the ancient Indus and sacred Ganges.
The mystic Saraswatti, which once flowed through Rajputana to the sea, has long ages ago disappeared through the desiccating action of the summer solstice-or "standing still ” of the sun over that country between May and July. The evaporating away of this river of Hindu poetry is a proof of how little anphilosophical political agitators take