Enough; the time was already ripe for a public demonstration of the new invention, and accordingly the 5th of the following June witnessed the ascent of the same balloon with due ceremony and advertisement. Special pains were taken with the inflation, which was conducted over a pit above which the balloon envelope was slung; and in accordance with the view that smoke was the chief lifting power, the fuel was composed of straw largely mixed with wool. It is recorded that the management of the furnace needed the attention of two men only, while eight men could hardly hold the impatient balloon in restraint. The inflation, in spite of the fact that the fuel chosen was scarcely the best for the purpose, was conducted remarkable expedition, and on being released, the craft travelled one and a half miles into the air, attaining a height estimated at over 6,000 feet. From this time the tide of events in the aeronautical world rolls on in full flood, almost every half-year marking a fresh epoch, until a new departure in the infant art of ballooning was already on the point of being reached. It had been erroneously supposed that the ascent of the Montgolfier balloon had been due, not to the rarefaction of the air within it--which was its true cause--but to the evolution of some light gas disengaged by the nature of the fuel used. It followed, therefore, almost as a matter of course, that chemists, who, as stated in the last chapter, were already acquainted with so-called "inflammable air," or hydrogen gas, grasped the fact that this gas would serve better than any other for the purposes of a balloon. And no sooner had the news of the Montgolfiers' success reached Paris than a subscription was raised, and M. Charles, Professor of Experimental Philosophy, was appointed, with the assistance of M. Roberts, to superintend the construction of a suitable balloon and its inflation by the proposed new method. The task was one of considerable difficulty, owing partly to the necessity of procuring some material which would prevent the escape of the lightest and most subtle gas known, and no less by reason of the difficulty of preparing under pressure a sufficient quantity of gas itself. The experiment, sound enough in theory, was eventually carried through after several instructive failures. A suitable material was found in "lustring," a glossy silk cloth varnished with a solution of caoutchouc, and this being formed into a balloon only thirteen feet in diameter and fitted without other aperture than a stopcock, was after several attempts filled with hydrogen gas prepared in the usual way by the action of dilute sulphuric acid on scrap iron. The preparations completed, one last and all-important mistake was made by closing the stop-cock before the balloon was dismissed, the disastrous and unavoidable result of this being at the time overlooked.