No one can ever guess at the future of electrical invention. The recent marvelous development of the wireless telegraph, by which the impalpable ether is harnessed to man's service, is an indication of the wonders which may be expected in the future. It was our own Joseph Henry who, in 1842, discovered the electric wave--the "induction" upon which wireless telegraphy depends. He discovered that when he produced an electric spark an inch long in a room at the top of his house, electrical action was instantly set up in another wire circuit in the cellar. After some study, he saw and announced that the electric spark started some sort of action in the ether, which passed through floors and ceilings and all other intervening objects, and caused induction in the wires in the cellar. But wireless telegraphy was made a commercial possibility not by any great scientist, but by a young Italian named Marconi. Already experiments with wireless telephony are going forward, and another half century may see all the labor of the world performed by this wonderful and mysterious force which we call electricity. * * * * * From earliest times, man has longed to navigate the air. He has watched with envy the free flight of birds, and has tried to imitate it, usually with disastrous results. The balloon, of course, enabled him to rise in the air, but once there, he was at the mercy of every wind. More recently, balloons fitted with motors and steering gear have been devised, which are to some extent dirigible; but the real problem has been to fly as birds do without any such artificial aid as balloons provide. Experiments to solve this problem were begun several years ago by Professor S. P. Langley, of the Smithsonian Institution, under government supervision, and pointed the way to other investigators. He proved, theoretically, that air-flight was possible, provided sufficient velocity could be obtained. He showed that a heavier-than-air machine would sustain itself in the air if it could only be driven fast enough. You have all skipped flat stones across the water. Well, that is exactly the principle of the flying machine. As long as the stone went fast enough, it skipped along the top of the water, which sustained it and even threw it up into the air again. When its speed slackened, it sank. So the boy on skates can skim safely across thin ice which would not bear his weight for an instant if he tried to stand upon it. So, theoretically, it was possible to fly, but to reduce theory to practice was a very different thing. Professor Langley tried for years and failed. He built a great machine, which plunged beneath the waters of the Potomac a minute after it was launched. All over the world, inventors were struggling with the problem, but nowhere with any great degree of success. It remained for two brothers, in a little workshop at Dayton, Ohio, to produce the first machine which would really fly.