At the time I commenced these experiments, almost the only flying-machine which had really flown was a toy-like model, suggested by A. Pénaud, a young Frenchman of singular mechanical genius, who contributed to the world many most original and valuable papers on Aeronautics, which may be found in the journal “L’Aeronaute.” His aeroplane is a toy in size, with a small propeller [p008] whose blades are usually made of two feathers, or of stiff paper, and whose motive power is a twisted strand of rubber. This power maintains it in the air for a few seconds and with an ordinary capacity for flight of 50 feet or so, but it embodies a device for automatically securing horizontal flight, which its inventor was the first to enunciate.[11] Although Pénaud recognized that, theoretically, two screws are necessary in an aerial propeller, as the use of a single one tends to make the apparatus revolve on itself, he adopted the single screw on account of the greater simplicity of construction that it permitted. One of these little machines is shown as No. 11, Plates 1 and 2. ‹AB› is a stem about 2.5 mm. in diameter and 50 cm. long. It is bent down at each end, with an offset which supports the rubber and the shaft of the screw to which it is hooked. The screw ‹HH›^1 is 21 cm. in diameter, and has two blades made of stiff paper; two are preferable, among other reasons, because they can be made so that the machine will lie flat when it strikes in its descent. About the middle of ‹AB› there is a “wing” surface ‹DC›, 45 cm. long and 11 cm. broad, the ends ‹C› and ‹D› being raised and a little curved. In front of the screw is the horizontal rudder ‹GK› having a shape like that of the first surface, with its ends also turned up, and ‹inclined at a small negative angle with this wing surface›. Along its center is a small fin-like vertical rudder that steers the device laterally, like the rudder of a ship.