This performance must necessarily be compared with that of the aeroplanes, as, for instance, the Wright machine, which, with a 25 to 30 horse-power motor operating two 8-foot propellers, raises a weight of 1,050 pounds and propels it at a speed of 40 miles an hour for upward of 2 hours. Another form of helicopter is the Leger machine, so named after its French inventor. It has two propellers which revolve on the same vertical axis, the shaft of one being tubular, encasing that of the other. By suitable gearing this vertical shaft may be inclined after the machine is in the air in the direction in which it is desired to travel. [Illustration: The Vitton-Huber helicopter at the Paris aeronautical salon in 1909. It has the double concentric axis of the Leger helicopter and the propelling planes of the Cornu machine.] The gyropter differs from the Cornu type of helicopter in degree rather than in kind. In the Scotch machine, known as the Davidson gyropter, the propellers have the form of immense umbrellas made up of curving slats. The frame of the structure has the shape of a T, one of the gyropters being attached to each of the arms of the T. The axes upon which the gyropters revolve may be inclined so that their power may be exerted to draw the apparatus along in a horizontal direction after it has been raised to the desired altitude. The gyropters of the Davidson machine are 28 feet in diameter, the entire structure being 67 feet long, and weighing 3 tons. It has been calculated that with the proposed pair of 50 horse-power engines the gyropters will lift 5 tons. Upon a trial with a 10 horse-power motor connected to one of the gyropters, that end of the apparatus was lifted from the ground at 55 revolutions per minute--the boiler pressure being 800 lbs. to the square inch, at which pressure it burst, wrecking the machine. An example of the gyroplane is the French Breguet apparatus, a blend of the aeroplane and the helicopter. It combines the fixed wing-planes of the one with the revolving vanes of the other. The revolving surfaces have an area of 82 square feet, and the fixed surfaces 376 square feet. The total weight of machine and operator is about 1,350 lbs. Fitted with a 40 horse-power motor, it rose freely into the air. The ornithopter, or flapping-wing type of flying machine, though the object of experiment and research for years, must still be regarded as unsuccessful. The apparatus of M. de la Hault may be taken as typical of the best effort in that line, and it is yet in the experimental stage. The throbbing beat of the mechanism, in imitation of the bird’s wings, has always proved disastrous to the structure before sufficient power was developed to lift the apparatus.