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 s.p.a.ce, 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 const.i.tuted as to be able to see, say, c.u.mulus ma.s.ses 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 gra.s.s 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 const.i.tution 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 Ess.e.x, 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 s.p.a.ce 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.
CHAPTER XXIX. CONCLUSION.
The future development of aerostation is necessarily difficult to forecast. Having reviewed its history from its inception we have to allow that the balloon in itself, as an instrument of aerial locomotion, remains practically only where it was 120 years ago. Nor, in the nature of the case, is this to be wondered at. The wind, which alone guides the balloon, is beyond man"s control, while, as a source of lifting power, a lighter and therefore more suitable gas than hydrogen is not to be found in nature.
It is, however, conceivable that a superior mode of inflation may yet be discovered. Now that the liquefaction of gases has become an accomplished fact, it seems almost theoretically possible that a balloonist may presently be able to provide himself with an unlimited reserve of potential energy so as to be fitted for travel of indefinite duration. Endowed with increased powers of this nature, the aeronaut could utilise a balloon for voyages of discovery over regions of the earth which bar man"s progress by any other mode of travel. A future Andree, provided with a means of maintaining his gas supply for six weeks, need have no hesitation in laying his course towards the North Pole, being confident that the winds must ultimately waft him to some safe haven. He could, indeed, well afford, having reached the Pole, to descend and build his cairn, or even to stop a week, if he so desired, before continuing on his way.
But it may fairly be claimed for the balloon, even as it now is, that a great and important future is open to it as a means for exploring inaccessible country. It may, indeed, be urged that Andree"s task was, in the very nature of the case, well nigh impracticable, and his unfortunate miscarriage will be used as argument against such a method of exploration. But it must always be remembered that in Andree"s case the rigours of climate which he was compelled to face were the most serious of all obstacles to balloon travel. The extreme cold would not only cause constant shrinkage of the gas, but would entail the deposition of a weight of moisture, if not of snow, upon the surface of the balloon, which must greatly shorten its life.
It would be entirely otherwise if the country it were sought to explore were in lower lat.i.tudes, in Australia, or within the vast unknown belt of earth lying nearer the equator. The writer"s scheme for exploring the wholly unknown regions of Arabia is already before the public. The fact, thought to be established by the most experienced aeronauts of old times, and already referred to in these pages, that at some height a strong west wind is to be found blowing with great constancy all round the globe, is in accordance with the view entertained by modern meteorologists. Such a wind, too, may be expected to be a fairly fast wind, the calculation being that, as a general rule, the velocity of currents increases from the ground at the rate of about three miles per hour for each thousand feet of height; thus the chance of a balloon drifting speedily across the breadth of Arabia is a strong one, and, regarded in this light, the distance to be traversed is certainly not excessive, being probably well within the lasting power of such a balloon as that employed by Andree. If, for the sake of gas supply, Aden were chosen for the starting ground, then 1,200 miles E.N.E. would carry the voyager to Muscat; 1,100 miles N.E. by E. would land him at Sohar; while some 800 miles would suffice to take him to the seaboard if his course lay N.E. It must also be borne in mind that the Arabian sun by day, and the heat radiated off the desert by night, would be all in favour of the buoyancy of the balloon.
But there are other persistent winds that, for purposes of exploration, would prove equally serviceable and sure. From time immemorial the dweller on the Nile has been led to regard his river in the light of a benignant deity. If he wished to travel down its course he had but to entrust his vessel to the stream, and this would carry him. If, again, he wished to retrace his course, he had but to raise a sail, and the prevalent wind, conquering the flood, would bear him against the stream.
This constant north wind, following the Nile valley, and thence trending still southward towards Uganda, has been regarded as a means to hand well adapted for the exploration of important unsurveyed country by balloon. This scheme has been conceived and elaborated by Major B.F.S.
Baden-Powell, and, so far, the only apparent obstacle in the way has proved the lack of necessary funds.
It will be urged, however, that for purposes of exploration some form of dirigible balloon is desirable, and we have already had proof that where it is not sought to combat winds strongly opposed to their course such air ships as Santos-Dumont or Messrs. Spencer have already constructed acquit themselves well; and it requires no stretch of imagination to conceive that before the present century is closed many great gaps in the map of the world will have been filled in by aerial survey.
But, leaving the balloon to its proper function, we turn to the flying machine properly so called with more sanguine hopes of seeing the real conquest of the air achieved. It was as it were but yesterday when the air ship, unhampered by huge globes of gas, and controlled by mechanical means alone, was first fairly tried, yet it is already considered by those best able to judge that its ultimate success is a.s.sured.
This success rests now solely in the hands of the mechanical engineer.
He must, and surely can, build the ship of such strength that some essential part does not at the critical moment break down or carry away.
He may have to improve his motive power, and here, again, we do not doubt his cunning. Motor engines, self-contained and burning liquid fuel, are yet in their infancy, and the extraordinary emulation now existing in their production puts it beyond doubt that every year will see rapid improvement in their efficiency.
We do not expect, nor do we desire, that the world may see the fulfilment of the poet"s dream, "Argosies of magic sails" or "Airy navies grappling in the central blue." We would not befog our vision of the future with any wild imaginings, seeking, as some have done, to see in the electricity or other hidden power of heaven the means for its subjugation by man; but it is far from unreasonable to hope that but a little while shall pa.s.s, and we shall have more perfect and reliable knowledge of the tides and currents in the vast ocean of air, and when that day may have come then it may be claimed that the grand problem of aerial navigation will be already solved.