The inventor was prevented by other business, and by the want of a sufficiently large open space, from continuing his experiments, which had demonstrated that a large machine heavier than air could be made to lift itself and move at high speed. Misfortune alone prevented its true capacities being shown. Another experimenter on similar lines, but on a less heroic scale than Sir Hiram Maxim, is Professor S. P. Langley, the secretary of the Smithsonian Institution, Washington. For sixteen years he has devoted himself to a persevering course of study of the flying-machine, and after oft-repeated failures has scored a decided success in his Aerodrome, which, though only a model, has made considerable flights. His researches have proved beyond doubt that the amount of energy required for flight is but one-fiftieth of what was formerly regarded as a minimum. A French mathematician had proved by figures that a swallow must develop the power of a horse to maintain its rapid flight! Professor Langley’s aerodrome has told a very different tale, affording another instance of the truth of the saying that an ounce of practice is worth a pound of theory. A bird is nearly one thousand times heavier than the air it displaces. As a motor it develops huge power for its weight, and consumes a very large amount of fuel in doing so. An observant naturalist has calculated that the homely robin devours per diem, in proportion to its size, what would be to a man a sausage two hundred feet long and three inches thick! Any one who has watched birds pulling worms out of the garden lawn and swallowing them wholesale can readily credit this. Professor Langley therefore concentrated himself on the production of an extremely light and at the same time powerful machine. Like Maxim, he turned to steam for motive-power, and by rigid economy of weight constructed an engine with boilers weighing 5 lbs., cylinders of 26 ozs., and an energy of 1 to 1-1/2 horse-power! Surely a masterpiece of mechanical workmanship! This he enclosed in a boat-shaped cover which hung from two pairs of aeroplanes 12-1/2 feet from tip to tip. The whole apparatus weighed nearly 30 lbs., of which one quarter represented the machinery. Experiments with smaller aerodromes warned the Professor that rigidity and balance were the two most difficult things to attain; also that the starting of the machine on its aerial course was far from an easy matter. A soaring bird does not rise straight from the ground, but opens its wings and runs along the ground until the pressure of the air raises it sufficiently to give a full stroke of its pinions. Also it rises _against_ the wind to get the full benefit of its lifting force. Professor Langley hired a houseboat on the Potomac River, and on the top of it built an apparatus from which the aerodrome could be launched into space at high velocity.