"So it is with the air," says Professor Langley. "Even the viewless air possesses inertia; it cannot be pushed aside without some effort; and while the portion which is directly under the air-ship would not keep it from falling several yards in the first second, if the ship goes forward so that it runs or treads on thousands of such portions in that time, it will sink in proportionately less degree; sink, perhaps only through a fraction of an inch." It is evident, therefore, that if, at a given speed, the horizontal wings of an air-ship would keep it from falling more than a fraction of an inch in a second, by increasing the speed sufficiently and giving the wings an upward inclination, the air-ship instead of falling might actually rise. And this, as we shall see presently, is just what the flying-machines of Sir Hiram Maxim and Professor Langley and of the Wright brothers and their imitators did do. LANGLEY'S EARLY EXPERIMENTS AND DISCOVERIES It was while making an important series of experiments with aeroplanes that Professor Langley made the discovery which has since been known as "Langley's Law." In effect this law is that while it takes a certain strain to sustain a properly disposed weight while stationary in the air, to advance the weight rapidly takes _even less strain_ than when the weight is stationary. Thus, contrary to opinions held until recently, and contrary to the rules for land vehicles and ships, the strain of resistance of an aeroplane will diminish instead of increasing with the increase of speed. Professor Langley proved this remarkable fact with a most simple but ingenious device. It consisted of an immense "whirling table," driven by an engine, so arranged that the end of a revolving arm could be made to travel at any speed up to seventy miles an hour. At the end of this arm, surfaces disposed like wings were placed, and whirled through the two hundred feet circumference, until they were supported like kites by the resistance of the air. A certain strain was, of course, necessary to support one of these winglike structures when stationary in the air, but, curiously enough, less strain was required when it was advanced rapidly. Thus a brass plate of proper shape weighing one pound was suspended from a pull-out spring scale, the arm of which was drawn out until it reached the one-pound mark. When the whirling table was rotated with increasing velocity the arm indicated less and less strain, finally indicating only an ounce when the speed of a flying bird was reached. "The brass plate seemed to float on the air," says Professor Langley, "and not only this, but taking into consideration both the strain and the velocity, it was found that absolutely less power was spent to make the plate move fast than slow, a result which seemed very extraordinary, since in all methods of land and water transport a high speed costs much more power than a slow one for the same distance."