.
Compressed air, forced through thousands of holes at the bottom of the
floats, was interposing a gaseous cushion between those floats and the
track, just as it could do between them and the earth wherever _Nissr_
should alight.

Suspended thus on a thin layer of air, perhaps no more than a
sixteenth of an inch thick but infinitely less friction-producing than
the finest ball-bearing wheels and quite incapable of being broken,
the ship now waited only the application of the power in her vast
propellers.

"Let in numbers two and four," commanded the Master, suddenly, into
the engine-room telephone. "In five seconds after we start, hook up
one and three; and five later, the other two."

"Aye, aye, sir," came back the voice of Auchincloss, chief engineer.
"Ready, sir!"

Almost at once, the vibration of the engines altered, grew more
marked, seemed to be taking hold of something with strong but easy
effort. Another trembling made itself felt, as two of the giant
screws, connected by reducing-gears with the engine-shafting--all
three engines being geared to one shaft, but any one being capable of
separate running--began to revolve.

From astern, a dull, droning hum mounted, rose, grew rapidly in volume
and power. And, as two more screws began to whirl, the Eagle of the
Sky shook herself slightly. She awoke from slumber. Steadily, smoothly
on her air-cushions she began to move forward down the long, sloping
trackway to the brink of the cliff.

"Lord above!" breathed Bohannan, chewing at his nails. "We're off!"

Neither the Master nor Captain Alden moved, spoke, manifested any
excitement whatever. Both might have been graven images of coolness.
The Celt, however, got up and leaned at the window-jamb, unable to
keep still. He turned suddenly to Alden.

"Come, man!" he exclaimed, half angrily. "Got no heart in you, eh? No
interest? Come along out of that, now, and see what's what!"

He laid hold on the captain, and drew him to the window as the airship
accelerated her plunge along the rails. The hum of the propellers
had now risen to a kind of throaty roar; the craft was shaking with
strange quivers that no doubt would cease if she but once could launch
herself into the air. Under her, in and in, the shining metal rails
came running swiftly and more swiftly still, gleaming silver-like
under the vivid beam of the searchlight.

Wind began to rise up against the glass of the pilot-house; the wind
of _Nissr's_ own mak