To most persons, even to the cautious and scientific inventor himself, the performance of this, and a second aerodrome which flew about three-quarters of a mile, seemed to show that the secret of aerial navigation was all but fathomed. "The world, indeed, will be supine," Langley wrote a short time after the success of his flying-machine, "if it does not realize that a new possibility has come to it, and that the great universal highway overhead is soon to be opened." What could be plainer? A machine of a certain construction, weighing some thirty pounds, and carrying at that some excess of weight, had been able to fly a relatively long distance. What easier than to construct a machine on precisely similar lines only ten, a hundred, a thousand times larger, until it would carry persons and cargo, and fly across an ocean or a continent? Professor Langley himself, as was most fitting, undertook the construction of such a man-carrying air-ship. And it was during this undertaking that he made the momentous discovery that seemed to oppose a question mark to the possibility of flight by the aeroplane principle. This discovery was an "unyielding mathematical law that the weight of such a machine increases as the cube of its dimensions, whereas the wing surface increases as the square." In other words, as the machine is made larger, the size of the wings must be increased in an alarmingly disproportionate ratio. And the best that Professor Langley's man-carrying flying-machine could do, after the inventor had expended the limit of his ingenuity, was to dive into the waters of Chesapeake Bay, instead of soaring through the air as its prototype, the aerodrome, had done. THE IMPOSSIBLE ACCOMPLISHED The plunge of Langley's aerodrome downward into the water instead of upward through space as had been confidently expected, carried with it the hopes of a great number of hitherto enthusiasts, who were now inclined to believe that the practical conquest of the air was almost as far beyond our reach as it had been beyond that of all preceding generations. Learned scientists were able to prove to their own satisfaction, by long columns of figures and elaborate mathematical calculations, that the air is unconquerable. [Illustration: THE WRIGHT AEROPLANE.