AIR, OR ATMOSPHERE.

Temuka Leader, Issue 391, 24 May 1881, Page 2

AIR, OR ATMOSPHERE.

[By W. W. Rowe.] [Concluded.] The atmosphere possesses the property of buoying up bodies which bulk for bulk are lighter than itself. The support afforded to. bodies in the atmospheric fluid by its. resistances is very evident from many appearances in nature, as the support of vapours or clouds, the rising of smoke and tine particles of dust and the flying of birds. In art it is exemplified by the flying of a boys paper kite,, the rising of soap bubbles and its buoyant property by the floating of balloons. The flight of birds is not accomplished altogether by the buoyant property of the air. These animals support themselves by striking their wings against the fluid through which they are passing and this friction along with the property of buoyancy in the atmosphere sustains n.them at any height to:which they are pleastd taasceriS. Birds do not general'y soar above half a mile in height and seldom above a few hundred yards. At considerable elevations the air is so specifically light as to be unsuitable for their easy support. Those which rise to the higher regions of the atmosphere, .as, for instance the eagle, are provided with large wings which enable them to support themselves in the comparatively thin fluid in which they move. A small bird when let out of a balloon at |hio height of three miles drops almost

like a plummet till it .arrives in a fluid?, against which its little wings can takeeffect. The buoyant property of the air thus obviously diminishes in proportion as it becomes less dense and there is a,, point above which the highest im iginable body or par'icle of matter would ijuvit- : ably sink. By this means ;of terrestrial, attraction an effectual limits has been set to the distance attainable: ;from the surface of* our planet. / Not an atom of matter since the period of the-, creation has been suffered to escape beyond: die higher regions of the atmosphere,, onwhich has not in making the attempt been brought back to theearth. Wind is simply air in motion- ; iind originates through variationsx»f tem-:-‘perature.. When through file agency of; the sun a particular portion of the earth's* surface is heated to a greater degree than the remainder,, the air resting upon it-4>e-comes rarefiied and ascends, while a T rent of cold air nushra* in to supply the * vacancy. There is aftsaysssome motion in the air but the violence of fhe motion is.perpetually varying: Every graduation/ exists in the speed of- winds from the mildest zephyr to the most violent hurricanerA~svindwhichis“BCarcely perceptible- - moves at the rate of about 1 miles perhour a gentlfe- wind! about 4: mile pervhour, in a brisk gale from 10 to fifteenndles per hour, in a high wind from 30 to* 35 miles per hour, in.a storm from 50 to--60 mile&.per hour, while in/ a hurricane the velocity is estimated at from 80 to--100-mifes.per hour. Different currents of? air exist atidifferent elevations, moving in. different directions with different velocities. Tn 1839 an English aeronaut at the height of 14,000 feet encountered a. current that bore him along at the rate: of 5 miles an hour but upon descending tothe altitude of 12000feet,hemet with a contrary wind blowing-with a. velocity of SO"' ' miles per hour .The most useful winds are the trade winds so-called because they arovery, convenient, to who haveto cross the ocean, as: they always blow in oee direction, Those iu the Hemisphere blow from N.E. and those..in. the Southern. Hemisphere blow from--B.E: In many parts of the- Pacific cm--braced within the region of the trade wind a- vessel may sail for a week, without; altering, the position of a sail or rope The- . hurricane- is the most disastrous andi dangerous of all winds and is aa exfcensive storm of wind revolving round an, axis, the whole body of the storm; having a progressive motion over the- surface- ofthe ocean the main path itself- being as, grand curve. The surface swept Byriliese tremendous whirlwinds is a vast circle: varying from 100 to 500 miles in diameter.. The great Cuba, hurricane of. 1844 was estimated to-have been not less; than 800> miles in: breadth and the area over which - it prevailed during its length, was comSP puted. to be 2,400,000 square miles. In. 1845 a ship encountered a hurricane nearMauritius.,* The wind as the ship sailed, in the circuit of the storm changed 5* times completely round in 117 hours,. The whole distance sailed by the vesselwas 1373 miles, and at the termination of : the storm she was only 354" miles from theplaca- where the storm commenced'. At the present day, though:a full theory has not yet been established concerning hurri.. canes the sailer has been taught to step out of their path, Rules have been published by which a sailor may know the exact course of the hurricane he may happen to encounter, which enable him, to. steer his.

ship so,that she can ride safely until the hurricane is gone. Without such knowledge, puzzled by the changing wind he- , perhaps drives before it and is whirled round, circle after circle dragged through, the very road of danger or he escapes into, the middle of the circle, has a little breathing time and presently the crash returns,or - he gets out of the main coarse, and’ through ignorance encounters it again..

Shipwrecks ip amenable have been caused in this way. A hurricane- is accompanied; in its course by thunder and- lightning, and torrents of rain. A sea breeze is caused by the land getting more heated than the sea, and the laud air becomes, hotter than that over the sea, in consequence of which the cooler sea air glides. » inland to restore the equilibrium. The pima winds are winds coming from the snowy peaks of the Andes, which sweep, over the high table lands of South, America. They are so extremely dry and cold,' that they absorb the moisture of' the dead animals’ bodies with such, rapidity as to prevent putridity. If a. mule happens to die on one of the plainsit is soon converted into a mummy eyery part being free from the slightest of decay. The Simoom is an intensely hot wind which prevails upon the vast, deserts of Africa and the arid plaina.of Asia, pausing great suffering, and. after, destruction) of whole caravans of men and- 1 animals. The origin of, - the simoon is to be sought in the peculiarities of, the soil and the geographical position, of countries where it occurs.. The. surfaceof the deserts of Africa and Asia, is composed of dry sand which the rays of. the sun render burning to the touch. -Thoheat of these regions is insupportable and; their atmosphere like the breath of a furnace. When under such circumstances, fie wind rises and sweeps over theseplains it is intensely hot and destitute of

moisture and at the same time bears aloft with it great clouds of fine sand and dust.

a dreadful visitant to the traveller. The* typhoon is a storm,of wind some.what s«k

fcemblipg the hurricane It is not met with only in the China seas. Tornadoes jua\ be regarded as hurricanes differ ng chiefly in respect to their continuance and extent. They usually last from 15 to 70 seconds. Their bre >dih varies from a few rods to several hundred yards, and the length of the course rarely exceeds miles. The tornado is generally preceded by a calm and salty state of tne atmosphere, when suddenly the whirlwind appears, prostrating everything before it. Tornadoes are usually accompanied by thunder and lightning, and sometimes by showers of hail. When fowls and other birds are caught in a tornado they are often stripped entirely of their feathers. A curious theory was propounded some years ago to account for this. The author of the theory supposed that in the vortex or centre of the tor-

nado there was a vacuum, and the birds being suddenly caught in it the air contained in the barrel of their quills ex- • panded with such force as to strip them from the body. (N.JB. —Poulterers might look out for tornadoes). Tornadoes are supposed to be produced by the lateral

action of an opposing wind or the influence of a brisk gale upon a portion of the atmosphere tu The whirl of the whirlwind appears to" originate in the upper regions of the atmosphere, increasing its velocity as it descends, its base gradually approaching the earth until it rests upon its surface. If winds should cease to blow over the ocean it is quite possible that the water would stagnate. Tempests and hurricanes also exercise a beneficial effect by agitating and purifying the atmosphere, sweeping from it the seeds of pestilence and contagion. Winds belong to the study of meteorology. I don’t think I can finish better than by

quoting an extract taken from a lesson by

Maury, who says ; —“ Enveloping this solid globe of ours are two oceans, one partial, the other universal. There is the ocean of water which has settled down into all the depressions of the earth’s surface, leaving high above it all the high lands ; and there is an ocean ot air, which inwraps the whole in one transparent mantle. Through the bosom of that ocean —like fishes with their fins, and whales

with their flippers—birds and other winged

creatures swim, whilst —like crabs, and many shell fish—man and other mammalia creep about at the bottom of this serial- sea. The air ocean which everywhere surrounds the earth, and feeds and nourishes it is even more simple, more grand, and more majestic than the world of waters, more varied and changeful in its nujpds of storm and calm, of ebb and fib*?, of brightness and gloom. The atmosphere is, indeed, a wonderful thing, a most perfect example of the economy of nature. Deprived of air no animal would live, no plant would grow, no would be liffused. The air, too, is the sole medium of sound. Without it, artillery might roar, mountains might fall, but it would be in perfect silence —neither whisper nor thunder would ever be heard. A philosopher of the East thus describes the atmosphere ;—“lt surrounds us on all sides, yet we see it not ; it presses on us with a load of fifteen pounds on every

square inch of surface of our bodies, yet we do not so much as feel its weight. Softer than the softest down, more im-

palpable than the finest gossamer, leaves the cabinet undisturbed, and scarcely stirs the lightest flower that feeds on the dew it supplies, yet it bears the fleets of nations on its wings around the world, and crushes the most refractory substances with its weight. When in motion its force is sufficient to level the most stately forests and stable buildings with the earth, to raise the waters of the ocean into ridges like mountains, and dash the strongest ships to pieces like toys. It bends the rays of the sun from their path to give us the twilight of evening and of dawn ; it disperses and refracts their various tints to beautify the approach and retreat of the orb of day. But for the atmosphere, sunshine would burst on us and fade at once, and at once remove us from midnight darkness to all the blaze of noon. We should have no twilight to soften and beautify the landscape, no clouds to shade us from the scorching heat, but the bald earth as it revolved on its axis would turn its tanned and weakened front to the full and unmitigated rays of the lord of day. It affords the gas which vivifies and warms our ■ frames,' and receives into itself that which ha? been polluted by use and is thrown off as noxious. It feeds the flame of life exactly as it does that of the fire, it is in both cases consumed and affords the food of consumption,” “ It is only the girdling encircling of air,” says another philosopher, •' that flows above and around all that makes the whole world kiti. The carbonic acid with which today our breathing fills the air to-morrow seeks its way round the world; The date trees that grow around the falls of the a e* will drink it in by their leaves ; the ars of Lebanon will take of it to add to their stature j the cocoanuts of Tahiti will grow rapidly upon it; and the palms and bananas of Japan will change it into flowers. The oxygen we are breathing was distilled for us a short time ago by the magnolias of the Susquehanna, and the great trees that skirt the Orinoco, and the Amazon ; the giant rhododendrons of the Himalayas contributed tc it ; and; the roses and myrtles of Cashmere, the cinnamon tree of Ceylon, and the forest older than the flood buried deep in the

heart of Africa. The rain we see descending was thawed for us out of the icebergs which have watched the polar star for ages, and i .>e imus lillies have soaked up from the Nile and exhaled as a vapor snows that rested on the summit of the

Alps.” There is no employment, more ennobling to man and his intellect than to trace the evidence of design and purpose in the Creator, which are visible in all parts of the creation. Hence, to him who studies the physical relations of earth, sea, and air, the atmosphere is something more than a shoreless ocean, at the bottom of which he creeps along. It is an envelope or covering for the dispersion of light and heat over the surface of the earth; it is a sewer into which with every breath we draw we cast vast quantities of dead animal matter; it is a laboratory for purification in which that matter is recompounded and wrought again into wholesome and healthfu shapes ; it is a machine for pumping up all the rivers from the sea, aud conveying the waters from their fountains in the ocean to their sources in the mountains ; it is an inexhaustible magazine marvellously adapted for benign and benificent purposes.