On testing the lifting power, A’s being full, that is containing 100,000 cubic feet of gas, will, after deducting the weight of balloon and two persons calculated at 1,000 pounds, with 3,000 pounds weight of ballast.
But B’s balloon would only have a 1,000 pounds of sand as compared with A’s, because B’s is only half full, having only 50,000 feet of gas in it.
Well, under these apparently opposite conditions, which balloon, do you suppose, would attain the greatest height?
I should say, paradoxical as it may appear, that they would reach about the same height, because the space left for expansion in B’s balloon, owing to its half filled state, would admit of the gas doubling its volume, while A’s balloon, being filled at starting, would from the first irrecoverably lose gas from the neck, although it remained full to the safety valve.
B’s would hold its own 50,000 feet, and it would quickly increase and multiply up to 100,000 cubic feet, and thus equal A’s balloon.
The store of ballast would soon be equal. A’s 3,000 pounds would, at three and three quarter miles high, be reduced to the level of B’s, which was 1,000 pounds at starting, with only 50,000 cubic feet of gas.
I have frequently adopted this system, but as I shall advert in the next part of my experiences to cases in point, I prefer now to refer to two of Mr. Green’s high ascents in proof of the practicability and objects of this method, which saves labour in casting out so much sand, and saves expense as well.
The two voyages of Green, which were made in the years 1838-9, have altogether escaped notice in the recent reviews of the most remarkable scientific ascents in the present century.
Robertson’s, Gay-Lussac’s, Bixio’s, and Barral’s having been mentioned, but not those of Green, which came after the ascents of above experimenters, and long before the fatal one by Croce Spinelli and Sivel, and that lately made by Captain Jovis and Lieutenant Mallet.
On the 4th of September, 1838, the celebrated Nassau balloon, which at that time was the property of Messrs. Gye & Hughes, the proprietors of Vauxhall Gardens, ascended from them with Mr. Green, Mr. Edward Spencer, and Mr. Rush of Elsenham Hall, Essex, the latter gentleman having engaged the balloon for experimental purposes, and more particularly on this occasion for ascertaining the greatest altitude that could with safety be attained with three persons in the car; and further to ascertain the changes of temperature that would take place at different elevations, as well as the variations of the currents of air; and finally, to establish the important fact, as to whether the same difficulties with regard to respiration in a very rarified atmosphere would be experienced by persons rising in a balloon to any great altitude, as have been felt by persons who have ascended lofty mountains, and by previous aërial travellers in balloons to great heights.