ASCENT, OVER FIVE MILES HIGH, BY GREEN AND RUSH.
I have before me a mass of leading articles and newspaper cuttings alluding to the ascent of Messrs. Jovis and Mallet, in which honourable mention is made of the lofty explorations by Robertson and L’Hoest, Gay-Lussac, Bixio, and Barral, together with Mr. Glaisher’s and my own, but Green’s with Rush are invariably omitted, and yet these were quite as important, while the second was higher than that made by the intrepid French balloonists, and, so far as physical results go, the Englishmen do not appear to have fainted or been much troubled.
It is of immense importance to note this, as there can be no doubt that a certain zone exists, in entering which some persons are more susceptible than others to lessened atmospheric pressure, and here they begin to feel the bad effects, which, by the way may come on without warning, just as it is with Alpine travellers, although there are marked distinctions between the two, but we cannot enter upon that in detail in this chapter.
This trip, by Green, was one of those which was designed to add a fraction of knowledge to the already existing stores of science. This fact is sufficient, even according to those who are not great admirers of ballooning, to warrant its encouragement when taken in hand by those who do not affect to be mere aëronautic performers, embarking in aërostatic pursuits for sensational objects, or with the vain and delusive idea, that it is not dangerous, and that it is a money-making concern.
Mr. Rush, assisted by the knowledge of his coadjutor, threw a character of deep interest over the whole subject of aërostation, and this trip, though lost sight of, at the present moment, is well worthy of re-production, serving as it does, two ends; firstly, to call attention to the fact, that English aëronauts seem to get more toughened by acclimatization to rarified air than Frenchmen, and secondly, that they do such work with less ado, and with equal, perhaps a little more, methodical foresight and precision, than our more dashing and mercurial neighbours.
It was on the 10th of September (what a number of exceptionable journeys were made in this month!) that the highest ascent which had been made up to that date, came off from the far-famed Vauxhall Gardens.
The proprietors made arrangements with Mr. Rush for it to take place in the afternoon, that gentleman engaging the car for the occasion.
The time allowed for preparation was limited. The first object to be gained was that of diminishing the weight of the apparatus to as low a point as due regard to their personal safety would admit.
A small car was substituted for that commonly used. At five o’clock in the afternoon, Green ascertained the power of the gas with which the “Nassau” balloon was charged, the tranquil state of the weather rendered this an easy operation.
On examination, Green found that the whole weight of the balloon and its appendages was 4,084 pounds thus constituted:
| Balloon, netting and car | 700 | pounds. |
| Ballast | 1,500 | ” |
| Mr. Rush | 145 | ” |
| Mr. Green | 145 | ” |
| Light, grapnel and rope | 52 | ” |
| Cloaks and barometers, &c. | 30 | ” |
| Twenty-seven half-hundredweights slung round the hoop | 1,512 | ” |
| ——— | ||
| Total | 4,084 | ” |
| ====== |
Please to note that Green then opened the upper valve, and discharged a quantity of gas equal to the power of the twenty-seven half-hundredweights, which were then removed from the hoop.
Why, you will ask, was this gas wasted, or put into the balloon? I suppose for the sake of appearances and symmetrical distention, but had Rush not been paymaster, it would most assuredly never have entered.
The departure took place with an ascending power of 112 pounds—very considerable indeed.
Barometer stood at 30·50 just before leaving, and thermometer at 60°; before seven minutes had elapsed, they had fallen, the former to 20, and the latter to 36°, equal to 11,000 feet or two miles.
Had it not been for the miserable aspect the balloon would have presented, more gas would have been let off equal to an additional 1,000 pounds, and then not more than 500 pounds of sand need have been shipped.
At 11,000 feet they were driven south, after going north-east.
Green was continually casting out ballast; on attaining 16,000 feet—three miles—they entered a current blowing at the estimated speed of sixty miles an hour, though they never stated, more’s the pity, how under such a rocket-like rush upwards, they found time to determine that this wonderful current existed.
The only inconvenience (this is noteworthy) Mr. Rush sustained, arose from the constant escape of gas from the rapid ascent.
Mr. Green suffered severely from the cold in his hands and feet.
They were now exposed to the influence of roaring winds, but from what I can make out, it was only the effect of quick vertical ascent; here the aëronaut, owing to the exertion he had to undergo, found it a matter of the utmost difficulty to fetch his breath.
The greatest altitude reached was 27,146 feet, indicating an elevation from the earth of 5 miles and 746 feet, the barometer, at this point having fallen from 30·50 to 11, and the thermometer from 61° to 5° or 27° below the freezing point.
Ballast had been reduced to something under seventy pounds, which Green resolved on preserving, and the result of their descent, which was never minutely entered into, proved the propriety of this reservation.
In the descent, they discovered something which very much bore the appearance and consistency of snow. Mr. Rush’s attention was called to it, but after consideration they were inclined to think that the substance was not snow, but the dew and moisture congealed by the cold.
It would be instructive to know how Captain Jovis, who must have had the night dew on his balloon at the early inflation in Paris, got on in this respect. His idea was that the sun would dry the moisture, but I was under the impression that there would scarcely be time for a globular shaped machine to get dry all round during the inflation. However, they may, like Green, have encountered a snow storm without there being, as indeed was unlikely, any damp clouds overhead at that elevation; what I mean is, if the balloon itself shed and shook off innumerable particles of frozen moisture, there can be no wonder that such was noticed and mistaken for a fall of snow.
After Rush and Green had hovered over Lewes in Sussex, a descent was effected near Southover; there was not much hovering I should say.
In this ascent they had the double advantage of witnessing the setting sun (prior to their quitting the earth) and on their reaching 12,500 feet of being once more within the sun’s rays.
Another important consideration bearing upon this chapter is the celerity with which balloons make their ascent.
It is obvious that the efficient power of ascension, or the excess of the whole buoyant force above the absolute weight of the apparatus, would, by acting constantly, produce always an accelerated motion. But this is very soon checked, and a uniform progress maintained by the increasing resistance which the huge mass must encounter in its passage through the air.
The velocity which a balloon would gain from unobstructed acceleration must, from the theory of dynamics, be to that which a falling body acquires in the same time as the efficient buoyancy is to the aggregate weight of the apparatus and of the contained fluid. Thus, if a balloon were to rise with a force equal to the eighth part of its compound weight, the celerity resulting from a constant acceleration would be expressed by multiplying four feet into the number of seconds elapsed since it was launched into the air. Its advance, however, being opposed, the balloon though still affected with partial oscillations, the final velocity is effected in perhaps little more than double the time required without such obstruction.
This final velocity, or the velocity at which the ascent becomes uniform, the resistance from the air being then equal to the efficient buoyancy of the balloon, is easily calculated.
The resistance a circle encounters in moving through any fluid in the direction perpendicular to its plane, is measured by the weight of a column of that fluid, having the circle for its base, and an altitude equal to the height from which a heavy body in falling would acquire the given celerity.
Near the level of the sea, and at the mean temperature, a column of atmospheric air seventeen feet high, and incumbent on a circle of one foot in diameter, weighs a pound avoirdupois, which is, therefore, the resistance that a circle would suffer if carried forwards with the celerity of thirty-three feet each second.
According to the same theory, however, which we owe to the sagacity of Newton, the resistance of a sphere is just the half of that of its generating circle, and consequently a velocity of forty-six and two-fifths feet in a second through the air would in ordinary cases create a resistance of one pound to a ball of one foot in diameter.
In other circumstances, the quantity of resistance must be proportional to the square of velocities, and of the diameters. Whence, if the buoyant power were always the same, the velocity of the ascent of a balloon would be inversely as its diameter.
I introduce these few observations, which are by a much higher authority than my own, because it occurred to me that my own remarks might be considered too homely for some of those who may read these lines, but as I have merely aimed at affording amusement with a moderate portion of instruction, and do not write for scientific men, but for general readers, I shall hope to gradually progress in this treatment in a subsequent volume.