ompared to boxes:

"The shape of a fish for the ship, the shape of a bird for the
flying-machine," he said.

He stuck to that principle and therefore he had added two enormous wings,
one on each side. He had first experimented with reduced models, shaped
like a bird, sending them up anyhow, to see, and he had ended by
constructing one which preserved its stability when gliding over the
atmospheric layers. He had thus been led to construct wings with a
slightly rounded surface whose coefficient of yield was nearly double that
of wings with flat surfaces. The width of these wings was about five feet
and their length about sixteen. They tapered a little, were drawn out in
front and widened at the opposite end, so as to get a more powerful hold
of the air. They were made of double-milled canvas, stretched on curved
ash and fastened to the sections by aluminum stays riveted with copper and
clenched. They were as light as they were stiff. These two wings pointed
slightly upward in front, parallel to the machine, and were fastened to it
in the middle by means of an axis below the saddle-pillar, which brought
their axis to the center of gravity. Other ingenious and quite individual
arrangements made the apparatus very manageable. The resistance of the
air, combined with the propelling power of the screw, exercised all its
force in vain: the wings remained stationary. Their lines were carefully
studied to facilitate the flow of the air, on the principle of Langley's
kite: and the two of them presented a carrying surface of forty-nine
square feet.

"It's not much," Jimmy explained to Lily, who listened attentively. "If I
carried my motor," he said, "I should have a bigger surface. The machine
ought then, theoretically speaking, to rise when it is going at a rate of
thirty miles an hour; with a good back push the front-wheel would leave
the ground and continue its course upward. But, on the stage, we have no
room to acquire speed: we shall get it from an inclined plane, as at the
start of 'Looping the Loop.' As for the side steering, the front wheel has
spokes fitted with canvas and offers resistance to the air: it will steer
the aerobike to left or right at a touch of the handle-bar, as in ordinary
riding, and there you are, Lily."

"My!" said Lily, bewildered by all this complicated apparatus. "Did you
work it all out on paper? It's enough to drive one mad!"

"When you're on it, Lily," said Jimmy, smiling, "you'll have to wo