Meanwhile the success achieved by the Tissandier brothers in 1881 and 1883 had inspired MM. Renard and Krebs, officers of the French army, who were stationed at Chalais-Meudon, near Paris. They had for several years been conducting experiments on the conditions requisite for directing balloons, being guided in their studies by the previous work of Dupuy de Lôme. An appropriation of one hundred thousand francs had been granted them, during Gambetta's brief administration, and their investigations were conducted with the utmost secrecy. The pecuniary resources at their command gave them a great advantage over Tissandier, in the ability to construct a balloon much larger than that with which Tissandier's success had been achieved; and this permitted the application of a motor nearly seven times as powerful as the one previously employed. Their balloon (Fig. 4) is one hundred and sixty-six feet long, twenty-eight feet in greatest diameter, its capacity sixty-seven thousand cubic feet, and ascensional power nearly five thousand pounds. The ratio of length to thickness is thus much greater than in Tissandier's balloon. The details of construction of the battery and motor have not been given to the public by Captain Renard. The rudder is almost a parallelogram in form, and thickest in the middle, the cloth being tightly stretched over a light framework so as to present a rigid surface to the air. The propeller is fixed to the extremity of a long shaft, and placed at the front, instead of rear, of the balloon. The front end of the machine is thicker than the rear end. This feature seems rather unaccountable. The balloon is filled with hydrogen, but within it is a subsidiary balloon, connected by a tube with the cage, where air can be pumped in or out at pleasure, thus varying slightly the specific gravity of the mass as a whole and enabling the aëronauts to vary their elevation at will.
On August 9, 1884, an ascent was accomplished with this balloon, the atmosphere being almost perfectly calm. A journey of nearly two miles was made in a southerly direction, then over a mile westward, after which the balloon was turned northward and eastward. Very slight motion of the rudder was needed to execute these curves. Twenty-three minutes after their flight was begun the aëronauts were immediately over their starting-point, having made a trip of not quite five miles. In descending it was necessary to move backward and forward several times in succession, alternately reversing the direction of rotation of the propeller. The return to the ground was at the very spot from which the departure had been made. This remarkable feat was thus accomplished almost exactly one hundred and one years after the ascent of the first hydrogen balloon, sent up by Charles from a point but a few miles distant.
A second ascent was made by Renard and Krebs on the 12th of September, but with only partial success, in consequence of an accident to the motor. On the 8th of November two successive journeys
