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 723 qualities of steel, I use aluminum, which, next to hydrogen, is the lightest substance known to industry: for the same reason, also, with the constant aim of diminishing the weight of the mechanism, I have adopted, as an essential part of the armored frame-work which supports the car and the aëronaut, a combination of pieces of pine-wood bound together by metallic threads so fine that they weigh almost nothing. So I was able to construct, in tubular form, the only aëroplane which has ever succeeded in raising itself and its aëronaut while remaining heavier than the air, about twenty kilogrammes being supported by the dynamic action of the propeller.

Nature sets us the example of this economy of weight in making hollow the quills of the feathers of birds, which must be at once light and solid—in making even their bones hollow, substituting air for the marrow of the bones of terrestrial animals.

If I were content to affirm the necessity of an apparatus heavier than the air, without at the same time insisting upon replacing by hydrogen, by aluminum and by threads of steel the heavy materials hitherto employed in the construction of flying-machines, I could have produced in a thousand different ways an aëroplane heavier than the air—so heavy that, like so many others, I should have remained on the ground, instead of flying around the lightning-rod of the Eiffel Tower.

Persuaded that the principle of aërostation and that of aviation do not in the least degree exclude each other, I have sought to unite them in the same mechanism, and, so doing, I think I have reconciled the two opposing schools of thought, which have struggled on paper, with no benefit to science, for the last hundred years. During four years of uninterrupted work, I have forced myself to solve practically the two fundamental problems, the equilibrium and the direction of balloons, deriving the ascensional force at the same time from the static action of the hydrogen and from the dynamic action of the screw.

With this end in view, I ballast my machine sufficiently to make it heavier by some pounds than the weight of the volume of air which it displaces. It cannot raise itself by the unaided effort of the hydrogen. From the propeller I demand the complement of necessary force. That is so real a factor, that, when I stop the motion of the propeller, the air-ship descends gently toward the earth by its own weight.