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 years 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.