These officers first worked out the separate elements in the design of their motor balloon before proceeding to build on a practical scale. They chose the torpedo form for their gas bag, thereby ensuring in the hull itself, projectile stability, and diminution of resistance. They placed the car near the envelope, thus minimizing the disturbing moment of the screw thrust, and the resistance of the suspension cords. They employed an extraordinarily powerful electric motor actuating a large screw so as to obtain a strong thrust with the least effort. In addition they adopted the best ideas of their predecessors in aëronautical design; the internal ballonet of Meusnier, and the close fitting cover of De Lome, with crossed suspension cords. But unfortunately they used an electric motor instead of some light engine. Finally, having carefully computed its requisite dimensions, they proceeded to construct the elegant air ship, _La France_, which was tested in 1884 and aroused anew the hope of ultimately conquering the air. Further details of this successful ship are of interest. Its hull was 165 feet long, 27.5 feet in greatest diameter, at one fourth the distance from its front end, and cubed 66,000 feet, thus having a buoyancy of two long tons. It was kept rigid under varying conditions, by means of a ballonet filled with air driven in by a common fan blower coupled to the motor. Beneath the envelope, a long narrow rectangular car made of bamboo, covered with silk, was suspended from the cords of the balloon cover which embraced the hull throughout nearly its entire length. The car was 108 feet long and 6 to 7 feet across, carried at its forward end the propeller, at its rear a rectangular rudder, and between them the aëronauts and the batteries and electric motor. A sliding weight was used to alter the poise of the ship, and a guide-rope to soften its descent. The electric motor and battery which furnished the propulsive power were designed expressly for such use, and were considered at the time to be remarkably light and effective. The motor, which was designed with the assistance of M. Gramme, weighed 220.5 pounds, and developed nine horse power. The battery, composed of chlorochromic cells, was the result of the researches of Renard himself. Having made a careful study of the best geometrical arrangement of the parts of the cell, Renard found that this battery would deliver to the shaft one horse power for each eighty-eight pounds of its weight. Thus the power plant rivaled in lightness the steam engine of Giffard, and at the same time was free from danger; but apparently it could not be much reduced in weight, whereas Giffard’s steam-power plant could be reduced tenfold, as shown by Renard’s contemporaries.