e of black gas. But they were converging oddly. And there was no
sight of the airplanes that Dick had just seen taking off from the
invisible tarmac.

* * * * *

Dick fired two Very lights as a signal to his flight to scatter. What
were they doing, bunching together like a flock of sheep, when at any
moment the enemy planes might come swooping in, riddling them with
bullets? He thrust the stick forward--and then realized that his
controls had gone dead!

He thought for a moment that a wire had snapped. But the stick
responded perfectly to his hand, only it had no longer control over
his plane. He kicked right rudder, and the plane remained motionless.
He pushed home the soaring lever, to neutralize the helicopter and the
plane still soared.

Then he noticed that the needle of his earth-inductor
compass-indicator was oscillating madly, and realized that it was not
his plane that was at fault.

Underneath him, his flight seemed to be milling wildly as the ships
turned in every direction of the compass. But not for long. They were
nosing in, until the whole flight resembled an enormous airplane
engine, with twelve radial points, corresponding to their propellers,
and the noses pointing symmetrically inward, like a herd of game,
yarding in winter time.

And now the true significance came home to Dick. A vertical line of
magnetic force, an invisible mast, had been shot upward from the
ground. The airplanes were moored to it by their noses, as effectively
as if they had been fastened with steel wires.

And he, too, was struggling against that magnetic force that was
slowly drawing him, despite his utmost efforts, to a fixed position
five hundred feet above his flight.

* * * * *

For a few moments, by feeding his engine gas to the limit, Dick
thought he might have a chance of escaping. Her nose a fixed point,
Dick whirled round and round in a dizzy maze, attempting to break that
invisible mooring-chain. Then suddenly the engine went dead. He was
trapped helplessly.

He saw old Evans gesticulating wildly in the front cockpit. The old
man hoisted himself, leaned over the cowling gibbered in Dick's ear.
The silent engine had ceased to throb, and the old man's shouts were
simply not translated into sound.

Suddenly the flight beneath jerked downward, just as a flag jerks when
it is hauled down a pole. They vanished into the dark cloud beneath.
At the sa