"There," said he, as he put the finishing touches to the apparatus, "you see that she is a combination of two principles—those of the Aëronef and the Aëroplane. The first reached its highest development in Jules Verne's imaginary "Clipper of the Clouds," and the second in Hiram Maxim's Aëroplane. Of course, Jules Verne's Aëronef was merely an idea, and one that could never be realised while Robur's mysterious source of electrical energy remained unknown—as it still does.
"Maxim's Aëroplane is, as you all know, also an unrealised ideal so far as any practical use is concerned. He has succeeded in making it fly, but only under the most favourable conditions, and practically without cargo. Its two fatal defects have been shown by experience to be the comparatively overwhelming weight of the engine and the fuel that he has to carry to develop sufficient power to rise from the ground and progress against the wind, and the inability of the machine to ascend perpendicularly to any required height.
"Without the power to do this no air-ship can be of any use save under very limited conditions. You cannot carry a railway about with you, or a station to get a start from every time you want to rise, and you cannot always choose a nice level plain in which to come down. Even if you could the Aëroplane would not rise again without its rails and carriage. For purposes of warfare, then, it may be dismissed as totally useless.
"In this machine, as you see, I have combined the two principles. These helices on the masts will lift the dead weight of the ship perpendicularly without the slightest help from the side-planes, which are used to regulate the vessel's flight when afloat. I will set the engines that work them in motion independently of the others which move the propellers, and then you will see what I mean."
As he spoke, he set one part of the mechanism working. Those watching saw the three helices begin to spin round, the centre one revolving in an opposite direction to the other two, with a soft whirring sound that gradually rose to a high-pitched note.
When they attained their full speed they looked like solid wheels, and then the air-ship rose, at first slowly, and then more and more swiftly, straight up from the table, until it strained hard at the piece of cord which prevented it from reaching the roof.
A universal chorus of "bravas" greeted it as it rose, and every eye became fixed on it as it hung motionless in the air, sustained by its whirling helices. After letting it remain aloft for a few minutes Arnold pulled it down again, saying as he did so—
"That, I think, proves that the machine can rise from any position where the upward road is open, and without the slightest assistance of any apparatus. Now it shall take a voyage round the room.
"You see it is steered by this rudder-fan under the stern propeller. In the real ship it will be worked by a wheel, like the rudder of a sea-going vessel; but in the model it is done by this lever, so that I can control it by a couple of strings from the ground."
He went round to the other side of the table while he was speaking, and adjusted the steering gear, stopping the engines meanwhile. Then he put the model down on the floor, set all four engines to work, and stood behind with the guiding-strings in his hands. The spectators heard a louder and somewhat shriller whirring noise than before, and the beautiful fabric, with its shining, silvery hull and side-planes, rose slantingly from the ground and darted forward down the room, keeping Arnold at a quick run with the rudder-strings tightly strained.