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."
These experiments, which destroyed the calculations of Newton, long held to be correct, showed that mechanical flight was at least theoretically possible, indicating as it did that a weight of two hundred pounds could be moved through the air at express-train speed with the expenditure of only one horse-power of energy. Since engines could be constructed weighing less than twenty pounds to the horse-power, theoretically such an engine should support ten times its own weight in horizontal flight in an absolute calm. As a matter of fact there is no such thing as an absolute calm in nature, air-currents being constantly stirring even on the calmest day, and this introduces another element in attaining aerial flight that is an all-important one. Indeed it has long been recognized that the mechanical power for flight is not the only requisite for flying—there is, besides, the art of handling that power.