In the launching of gliders, some French experimenters showed ingenuity. The brothers Voisin, for instance, who played a prominent part in the early tests in France, adopted the plan illustrated in Fig. 38. The gilder was towed by a motor-car across an open stretch of ground; then, when its speed was sufficient for the planes to lift, it rose and flew behind the car like a kite. Another form of glider, seen in Fig. 39, was mounted upon hollow wooden floats--anticipating the sea-plane of to-day--and towed upon the river Seine by a motor-boat. This gilder also, when its speed became sufficient, rose into the air. In the construction of the machine, a biplane, one notes resemblances to the method of the Wrights; and yet generally the craft is dissimilar. There are, of course, the two main-planes--characteristic of all machines of this type. Projecting in front of the planes, also, there is an elevator on the same principle as that of the Wrights. But between the main-planes are fixed four upright planes, or curtains as they were called. These were to preserve sideway balance, and prevent the machine from rolling when in flight. Should the craft tend to heel over, the surfaces of these planes--acting sideways upon the air--resisted such a movement. No wing-warping, such as the Wrights used, was fitted to this glider; the vertical planes alone were relied upon for sideway balance. The tail of the machine was a reproduction of the main-planes on a smaller scale, having two horizontal and three vertical surfaces. The theory of these rear-planes was that of the balancing tail such as is fitted to a kite; they steadied the machine automatically when in the air, and checked any tendency to dive. In 1905 a glider of this type was tested on the Seine; but it was not until 1906, at a time when the Wright aeroplane was capable of long flights, that a real French success was obtained; and then the flights made were brief, and carried out with a craft that was admittedly crude. It was a biplane of curious construction, built by the Voisin brothers for M. Santos-Dumont--a rich Brazilian who had spent money freely upon airships, and had been occupied, for some time before the Voisins made him this machine, with a craft having propellers to lift it vertically from the ground. Abandoning this idea, he devoted himself to the machine the Voisins built, which is seen in Fig. 40. Here are the same box-kite main-planes, with vertical curtains between them, as shown in the illustration of the Voisin glider. But now, to give the machine more sideway stability, these main-planes are tilted up at a pronounced dihedral angle. [Illustration: FIG. 40.--Santos-Dumont’s Biplane which flew at Bagetelle.]