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   Chapter 28 THE CONSTITUTION OF THE AIR.

The Dominion of the Air: The Story of Aerial Navigation By John M. Bacon Characters: 18217

Updated: 2017-12-01 00:02


Some fair idea of the conditions prevailing in the upper air may have been gathered from the many and various observations already recorded. Stating the case broadly, we may assert that the same atmospheric changes with which we are familiar at the level of the earth are to be found also at all accessible heights, equally extensive and equally sudden.

Standing on an open heath on a gusty day, we may often note the rhythmic buffeting of the wind, resembling the assault of rolling billows of air. The evidence of these billows has been actually traced far aloft in balloon travel, when aeronauts, looking down on a wind-swept surface of cloud, have observed this surface to be thrown into a series of rolls of vapour, which were but vast and veritable waves of air. The interval between successive crests of these waves has on one occasion been estimated at approximately half a mile. We have seen how these air streams sometimes hold wide and independent sway at different levels. We have seen, too, how they sometimes meet and mingle, not infrequently attended with electrical disturbance

Through broad drifts of air minor air streams would seem often literally to "thread" their way, breaking up into filaments or wandering rills of air. In the voyage across Salisbury Plain lately described, while the balloon was being carried with the more sluggish current, a number of small parachutes were dropped out at frequent intervals and carefully watched. These would commonly attend the balloon for a little while, until, getting into some minor air stream, they would suddenly and rapidly diverge at such wide angles as to suggest that crossing our actual course there were side paths, down which the smaller bodies became wafted.

On another occasion the writer met with strongly marked and altogether exceptional evidence of the vehemence and persistence of these minor aerial streamlets. It was on an occasion in April weather, when a heavy overcast sky blotted out the upper heavens. In the cloud levels the wind was somewhat sluggish, and for an hour we travelled at an average speed of a little over twenty miles an hour, never higher than 3,000 feet. At this point, while flying over Hertfordshire, we threw out sufficient ballast to cause the balloon to rise clear of the hazy lower air, and coming under the full influence of the sun, then in the meridian, we shot upwards at considerable speed, and soon attained an altitude of three miles. But for a considerable portion of this climb-while, in fact, we were ascending through little less than a mile of our upward course-we were assailed by impetuous cross currents, which whistled through car and rigging and smote us fairly on the cheek. It was altogether a novel experience, and the more remarkable from the fact that our main onward course was not appreciably diverted.

Then we got above these currents, and remained at our maximum level, while we floated, still at only a moderate speed, the length of a county. The descent then began, and once again, while we dropped through the same disturbed region, the same far-reaching and obtrusive cross-current assailed us. It was quite obvious that the vehement currents were too slender to tell largely upon the huge surface of the balloon, as it was being swept steadily onwards by the main wind, which never varied in direction from ground levels up to the greatest height attained.

This experience is but confirmation of the story of the wind told by the wind gauges on the Forth Bridge. Here the maximum pressure measured on the large gauge of 300 square feet is commonly considerably less than that on the smaller gauge, suggesting that the latter must be due to threads of air of limited area and high velocity.

Further and very valuable light is thrown on the peculiar ways of the wind, now being considered, by Professor Langley in the special researches of his to which reference has already been made. This eminent observer and mathematician, suspecting that the old-fashioned instruments, which only told what the wind had been doing every hour, or at best every minute, gave but a most imperfect record, constructed delicate gauges, which would respond to every impulse and give readings from second to second.

In this way he established the fact that the wind, far from being a body of even approximate uniformity, is under most ordinary conditions irregular almost beyond conception. Further, that the greater the speed the greater the fluctuations, so that a high wind has to be regarded as "air moving in a tumultuous mass," the velocity at one moment perhaps forty miles an hour, then diminishing to an almost instantaneous calm, and then resuming. "In fact, in the very nature of the case, wind is not the result of one simple cause, but of an infinite number of impulses and changes, perhaps long passed, which are preserved in it, and which die only slowly away."

When we come to take observations of temperature we find the conditions in the atmosphere above us to be at first sight not a little complex, and altogether different in day and night hours. From observations already recorded in this volume-notably those of Gay Lussac, Welsh, and Glaisher-it has been made to appear that, in ascending into the sky in daytime, the temperature usually falls according to a general law; but there are found regions where the fall of temperature becomes arrested, such regions being commonly, though by no means invariably, associated with visible cloud. It is probable, however, that it would be more correct not to interpret the presence of cloud as causing manifestation of cold, but rather to regard the meeting of warm and cold currents as the cause of cloud.

The writer has experimented in the upper regions with a special form of air thermometer of great sensibility, designed to respond rapidly to slight variations of temperature. Testing this instrument on one occasion in a room of equable warmth, and without draughts, he was puzzled by seeing the index in a capillary tube suddenly mounting rapidly, due to some cause which was not apparent, till it was noticed that the parlour cat, attracted by the proceedings, had approached near the apparatus. The behaviour of this instrument when slung in the clear some distance over the side of the balloon car, and carefully watched, suggests by its fitful, sudden, and rapid changes that warmer currents are often making their way in such slender wandering rills as have been already pictured as permeating the broader air streams. During night hours conditions are reversed. The warmer air radiated off the earth through the day has then ascended. It will be found at different heights, lying in pools or strata, possibly resembling in form, could they be seen, masses of visible cloud.

The writer has gathered from night voyages instructive and suggestive facts with reference to the ascent of air streams, due to differences of temperature, particularly over London and the suburbs, and it is conceivable that in such ascending streams may lie a means of dealing successfully with visitations of smoke and fog.

One lesson taught by balloon travel has been that fog or haze will come or go in obedience to temperature variations at low levels. Thus thick haze has lain over London, more particularly over the lower parts, at sundown. Then through night hours, as the temperature of the lower air has become equalised, the haze has completely disappeared, but only to reassert itself at dawn.

A description of the very impressive experience of a night sail over London has been reserved, but should not be altogether omitted. Glaisher, writing of the spectacle as he observed it nearly forty years ago, describes London seen at night from a balloon at a distance as resembling a vast conflagration. When actually over the town, a main thoroughfare like the Commercial Road shone up like a line of brilliant fire; but, travelling westward, Oxford Street presented an appearance which puzzled him. "Here the two thickly studded rows of brilliant lights were seen on either side of the street, with a narrow, dark space between, and this dark space was bounded, as it were, on both sides by a bright fringe like frosted silver." Presently he discovered that this rich effect was caused by the bright illumination of the shop lights on the pavements.

London, as seen from a balloon on a clear moonlight night in August a year ago (1901), wore a somewhat altered appearance. There were the fairy lamps tracing out the streets, which, though dark centred, wore their silver lining; but in irregular patches a whiter light from electric arc lamps broadened and brightened and shone out like some pyrotechnic display above the black housetops. Through the vast town ran a blank, black channel, the river, winding on into distance, crossed here and there by bridges showing as bright bands, and with bright spots occasionally to mark where lay the river craft. But what was most striking was the silence. Though the noise of London traffic as heard from a balloon has diminished of late yea

rs owing to the better paving, yet in day hours the roar of the streets is heard up to a great height as a hard, harsh, grinding din. But at night, after the last 'bus has ceased to ply, and before the market carts begin lumbering in, the balloonist, as he sails over the town, might imagine that he was traversing a City of the Dead.

It is at such times that a shout through a speaking trumpet has a most startling effect, and more particularly a blast on a horn. In this case after an interval of some seconds a wild note will be flung back from the house-tops below, answered and re-answered on all sides as it echoes from roof to roof-a wild, weird uproar that awakes suddenly, and then dies out slowly far away.

Experiments with echoes from a balloon have proved instructive. If, when riding at a height, say, of 2,000 feet, a charge of gun-cotton be fired electrically 100 feet below the car, the report, though really as loud as a cannon, sounds no more than a mere pistol shot, possibly partly owing to the greater rarity of the air, but chiefly because the sound, having no background to reflect it, simply spends itself in the air. Then, always and under all conditions of atmosphere soever, there ensues absolute silence until the time for the echo back from earth has fully elapsed, when a deafening outburst of thunder rises from below, rolling on often for more than half a minute. Two noteworthy facts, at least, the writer has established from a very large number of trials: first, that the theory of aerial echoes thrown back from empty space, which physicists have held to exist constantly, and to be part of the cause of thunder, will have to be abandoned; and, secondly, that from some cause yet to be fully explained the echo back from the earth is always behind its time.

But balloons have revealed further suggestive facts with regard to sound, and more particularly with regard to the varying acoustic properties of the air. It is a familiar experience how distant sounds will come and go, rising and falling, often being wafted over extraordinary distances, and again failing altogether, or sometimes being lost at near range, but appearing in strength further away. A free balloon, moving in the profound silence of the upper air, becomes an admirable sound observatory. It may be clearly detected that in certain conditions of atmosphere, at least, there are what may be conceived to be aerial sound channels, through which sounds are momentarily conveyed with abnormal intensity. This phenomenon does but serve to give an intelligible presentment of the unseen conditions existing in the realm of air.

It would be reasonable to suppose that were an eye so constituted as to be able to see, say, cumulus masses of warmer air, strata mottled with traces of other gases, and beds of invisible matter in suspension, one might suppose that what we deem the clearest sky would then appear flecked with forms as many and various as the clouds that adorn our summer heavens.

But there is matter in suspension in the atmosphere which is very far from invisible, and which in the case of large towns is very commonly lying in thick strata overhead, stopping back the sunlight, and forming the nucleus round which noisome fogs may form. Experimenting with suitable apparatus, the writer has found on a still afternoon in May, at 2,000 feet above Kingston in Surrey, that the air was charged far more heavily with dust than that of the London streets the next day; and, again, at half a mile above the city in the month of August last dust, much of it being of a gross and even fibrous nature, was far more abundant than on grass enclosures in the town during the forenoon of the day following.

An attempt has been made to include England in a series of international balloon ascents arranged expressly for the purpose of taking simultaneous observations at a large number of stations over Europe, by which means it is hoped that much fresh knowledge will be forthcoming with respect to the constitution of the atmosphere up to the highest levels accessible by balloons manned and unmanned. It is very much to be regretted that in the case of England the attempt here spoken of has rested entirely on private enterprise. First and foremost in personal liberality and the work of organisation must be mentioned Mr. P. Y. Alexander, whose zeal in the progress of aeronautics is second to none in this country. Twice through his efforts England has been represented in the important work for which Continental nations have no difficulty in obtaining public grants. The first occasion was on November 8th, 1900, when the writer was privileged to occupy a seat in the balloon furnished by Mr. Alexander, and equipped with the most modern type of instruments. It was a stormy and fast voyage from the Crystal Palace to Halstead, in Essex, 48 miles in 40 minutes. Simultaneously with this, Mr. Alexander dismissed an unmanned balloon from Bath, which ascended 8,000 feet, and landed at Cricklade. Other balloons which took part in the combined experiment were two from Paris, three from Chalais Meudon, three from Strasburg, two from Vienna, two from Berlin, and two from St. Petersburg.

The section of our countrymen specially interested in aeronautics-a growing community-is represented by the Aeronautical Society, formed in 1865, with the Duke of Argyll for president, and for thirty years under the most energetic management of Mr. F. W. Brearey, succeeding whom as hon. secs. have been Major Baden-Powell and Mr. Eric S. Bruce. Mr. Brearey was one of the most successful inventors of flying models. Mr. Chanute, speaking as President of the American Society of Civil Engineers, paid him a high and well-deserved compliment in saying that it was through his influence that aerial navigation had been cleared of much rubbish and placed upon a scientific and firm basis.

Another community devoting itself to the pursuit of balloon trips and matters aeronautical generally is the newly-formed Aero Club, of whom one of the most prominent and energetic members is the Hon. C. S. Rolls.

It had been announced that M. Santos-Dumont would bring an air ship to England, and during the summer of the present year would give exhibitions of its capability. It was even rumoured that he might circle round St. Paul's and accomplish other aerial feats unknown in England. The promise was fulfilled so far as bringing the air ship to England was concerned, for one of his vessels which had seen service was deposited at the Crystal Palace. In some mysterious manner, however, never sufficiently made clear to the public, this machine was one morning found damaged, and M. Santos-Dumont has withdrawn from his proposed engagements.

In thus doing he left the field open to one of our own countrymen, who, in his first attempt at flight with an air ship of his own invention and construction, has proved himself no unworthy rival of the wealthy young Brazilian.

Mr. Stanley Spencer, in a very brief space of time, designed and built completely in the workshops of the firm an elongated motor balloon, 75 feet long by 20 feet diameter, worked by a screw and petrol motor. This motor is placed in the prow, 25 feet away from, and in front of, the safety valve, by which precaution any danger of igniting the escaping gas is avoided. Should, however, a collapse of the machine arise from any cause, there is an arrangement for throwing the balloon into the form of a parachute. Further, there is provided means for admitting air at will into the balloon, by which the necessity for much ballast is obviated.

Mr. Spencer having filled the balloon with pure hydrogen, made his first trial with this machine late in an evening at the end of June. The performance of the vessel is thus described in the Westminster Gazette:-"The huge balloon filled slowly, so that the light was rapidly failing when at last the doors of the big shed slid open and the ship was brought carefully out, her motor started, and her maiden voyage commenced. With Mr. Stanley Spencer in the car, she sailed gracefully down the football field, wheeled round in a circle-a small circle, too-and for perhaps a quarter of an hour sailed a tortuous course over the heads of a small but enthusiastic crowd of spectators. The ship was handicapped to some extent by the fact that in their anxiety to make the trial the aeronauts had not waited to inflate it fully, but still it did its work well, answered its helm readily, showed no signs of rolling, and, in short, appeared to give entire satisfaction to everybody concerned-so much so, indeed, that Mr. Stanley Spencer informed the crowd after the ascent that he was quite ready to take up any challenge that M. Santos Dumont might throw down." Within a few weeks of this his first success Mr. Spencer was able to prove to the world that he had only claimed for his machine what its powers fully justified. On a still September afternoon, ascending alone, he steered his aerial ship in an easy and graceful flight over London, from the Crystal Palace to Harrow.

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