The smallest and lightest monoplane in practical use is that of M. Raoul Vendome. It is but 16 feet in spread, and is 16 feet fore and aft. It is equipped with a 12 horse-power motor, and flies at a speed of nearly 60 miles per hour. Without the pilot, its entire weight is but 180 pounds. The wings are pivoted so that their whole structure may be tilted to secure lateral balance. The new Moisant monoplane is built wholly of metal. The structure throughout is of steel, and the surfaces of sheet aluminum in a succession of small arches from the centre to the tips. No authentic reports of its performances are available. In the Tatin monoplane, also called the Bayard-Clement, the main plane is oval in outline, and the tail a smaller oval. The surfaces are curved upward toward the tips for nearly half their length in both the main plane and the tail. The propeller is 8½ feet in diameter, and is turned by a Clerget motor, which can be made to develop 60 horse-power for starting the machine into the air, and then cut down to 30 horse-power to maintain the flight. Chapter VII. FLYING MACHINES: OTHER FORMS. The triplane--The quadruplane--The multiplane--Helicopters--Their principle--Obstacles to be overcome--The Cornu helicopter--The Leger helicopter--The Davidson gyropter--The Breguet gyroplane--The de la Hault ornithopter--The Bell tetrahedrons--The Russ flyer. While the efforts of inventors have been principally along the lines of the successful monoplanes and biplanes, genius and energy have also been active in other directions. Some of these other designs are not much more than variations from prevailing types, however. Among these is the English Roe triplane, which is but a biplane with an extra plane added; the depths of all being reduced to give approximately the same surface as the biplane of the same carrying power. The tail is also of the triplane type, and has a combined area of 160 square feet--just half that of the main planes. The triplane type has long been familiar to Americans in the three-decker glider used extensively by Octave Chanute in his long series of experiments at Chicago. [Illustration: The Roe triplane in flight.] The quadruplane of Colonel Baden-Powell, also an English type, is practically the biplane with unusually large forward and tail planes. The multiplane of Sir Hiram Maxim should also be remembered, although he never permitted it to have free flight. His new multiplane, modelled after the former one, but equipped with an improved gasoline motor instead of the heavy steam-engine of the first model, will doubtless be put to a practical test when experiments with it are completed. [Illustration: Sir Hiram Maxim standing beside his huge multiplane.] Quite apart from these variants of the aeroplanes are the helicopters, ornithopters, gyropters, gyroplanes, and tetrahedral machines. HELICOPTERS.