When these researches were known and understood, their effect upon the practical handling of the problem of flight was immediate and decisive. The aeroplane, or gliding machine, had many rivals; they were all killed by Professor Langley's researches, which showed that the cheapest and best way to raise a plane in the air is to drive it forward at a small upward inclination; and that its weight can be best countered not by applying power to raise it vertically, but by driving it fast. In the statistical tables that he prepared he called the upward pressure of the air _Lift_; the pressure which retards horizontal motion he called _Drift_. The words make a happy pair, but the word _Drift_ is badly needed to describe the leeway of an aeroplane in a cross-wind, so that in England another pair of words, _Lift_ and _Drag_, has been authoritatively substituted. From this time onward Langley devoted himself to those other problems, especially the problems of balance, of mechanical power, and of safety in taking off and alighting, which had to be solved if he was to make a machine that should fly. He was much influenced, he says, by a mechanical toy, produced as early as 1871 by an ingenious Frenchman called Penaud, and named by its inventor the 'planophore'. This toy, which weighed only a little over half an ounce, was supported on wings, and was driven forward by an airscrew made of two feathers. The motive power was supplied by twisted strands of rubber which, as they untwisted, turned the airscrew. The wings were set at a dihedral angle, that is, they were bent upwards at the tips; and fore-and-aft stability was secured by a smaller pair of wings just in front of the airscrew. 'Simple as this toy looked,' says Professor Langley, 'it was the father of a future flying machine, and France ought to have the credit of it.' His own steam-driven flying machine was produced and successfully flown in 1896. It had two wings and a tail, with a supporting surface in all of seventy square feet; its total weight was seventy-two pounds; the engine, constructed by himself, weighed only seven pounds and developed one horse-power, which served to drive two airscrews, revolving in opposite directions. The best flight of this machine was more than three-quarters of a mile, and was made over the Potomac river. When, on its first flight, it had flown for a minute, 'I felt', says Professor Langley, 'that something had been accomplished at last, for never in any part of the world or in any period had any machine of man's construction sustained itself in the air before for even half of this brief time'. His flying machines were called by Langley 'aerodromes', and the word 'aeroplane' was used by him, as it is used in the _New English Dictionary_ of 1888, only in the sense of a single plane surface used for aerial experiments. But no usage, however authoritative, can withstand the tide of popular fashion; the machine is now an aeroplane,