“Well, I’ve been thinking a lot at odd times about airships and things, and reading up what they’ve been doing in France and Germany. There’s little prospect of making a really serviceable machine out of the old gas balloon; it’s far too clumsy; can’t make headway against a strong wind; but I didn’t see why something shouldn’t be done on the lines of the aeroplane. You see, it’s easy enough to set the thing going, and even to steer it, when you’ve got it up in the air; but there are three difficulties: to get it up, to let it down without smashing it to bits, and to keep it from turning somersaults. You can overcome the force of gravity by an arrangement of planes when you keep up a good speed; but if you slacken speed, down you come. And all the aeroplanes that have been invented yet can’t rise in the air at any given spot. They either have to be thrown off from some elevated position, or they have to get up a momentum along the ground, running like a motor-car. Then again, the motor machinery has been too heavy; engines haven’t been able to exert sufficient horse-power in proportion to their own weight. I’ve worked it out, and I calculate that no good can be done till you get an engine that’ll give you one horse-power to every two and a half pounds of its weight.” “Yes. Well?” “Well, this model is the result of no end of experiments. It goes, as you see; but besides sailing horizontally, it will lift itself. Look!” He took up the little machine, released another spring, and the miniature airship went flying to the ceiling, where it remained until the spring ran down. “All very well,” said Mr. Greatorex, unwilling to admit that he was impressed; “but the thing is only a _toy_. There’s all the difference in the world between a model and the _real thing_, you know. You could never get a spring strong enough to lift a real machine. I’m not satisfied that you could even get the horizontal motion you’re so cocksure of, with a machine that would carry _men_.” “No spring would do it, it is true; but I’ve worked out an application of the principle. It’s well known that a propeller rotating at sufficient speed can be made to lift a weight into the air. Of course we couldn’t set a real airship rotating bodily; no aeronaut’s head would stand it if we could. But, as you saw, my model doesn’t rotate itself. I’ve only made use of the principle—pretty successfully, don’t you think?” “Just explain to me _thoroughly_, will you? I want a little more _light_ on the subject.”