Screws opposing a slanting plane to the bed of air will produce an ascensional movement, and the models experimented on have shown that the disposable weight, that is to say the weight it is possible to deal with as distinct from that of the apparatus, increases with the square of the speed.

Herein the aeroplane has the advantage over the aerostat even when the aerostat is furnished with the means of locomotion.
Nevertheless Robur had thought that the simpler his contrivance the better.

And the screws--the Saint Helices that had been thrown in his teeth at the Weldon Institute--had sufficed for all the needs of his flying machine.

One series could hold it suspended in the air, the other could drive it along under conditions that were marvelously adapted for speed and safety.
If the ornithopter--striking like the wings of a bird--raised itself by beating the air, the helicopter raised itself by striking the air obliquely, with the fins of the screw as it mounted on an inclined plane.

These fins, or arms, are in reality wings, but wings disposed as a helix instead of as a paddle wheel.