ir.]

[Sidenote: From Space came Cor's disc-city of Vada--its mighty,
age-old engines weakening--its horde of dwarfs hungry for the Earth!]

In the burning solitude of the great Arizona desert, some two miles
south of Ajo, a young scientist was about to perform an experiment
that might have far-reaching results for humanity.

The scientist was Gordon Kendrick--a tall, tanned, robust chap who
looked more like a prospector in search of gold than a professor of
physics from the State University of Tucson.

Indeed, he was in a way, a prospector, since it was gold he
sought--some practical method of tapping the vast radio-energetic
treasure of the sun--and it was an apparatus designed to accomplish
just this that he was about to test.

The primary unit of the mechanism comprised a spheroidal vacuum-tube
measuring a little over a foot across its long axis, mounted in a
steel bracket that held it horizontal with the ground. Down through
its short axis ran a shaft on which was centered a light cross of
aluminum wire, carrying four vanes of mica, one face of each coated
with lampblack. A flexible cable led from the bottom of this shaft to
the base of the bracket, where it was geared to a small electric motor
driven by two dry cells. A rheostat-switch for delivering and
controlling the current was mounted nearby.

[Illustration]

At the wide arc of the egg-shaped tube was a concave platinum cathode,
at the narrow arc a nib of some sort, ending in a socket. From this
socket, two heavy insulated wires extended sixty feet or so across the
sand to the secondary unit of the mechanism, which was roughly a
series of resistance coils, resembling those in an ordinary electric
heater.

* * * * *

As Kendrick prepared to test this delicate apparatus that represented
so much of his time and thought, held so much of his hope locked up in
it, a turmoil was in his heart, though his brown face was calm.

If his theories were right, that revolving cross would tap and draw
into its vanes radio-energetic waves of force, much as the whirling
armature of a dynamo draws into its coils electro-magnetic waves of
force. For the blackened sides of the vanes, absorbing more radiation
than the bright sides, would cause the molecules to rebound from the
warmer surfaces with greater velocity, setting up an alternate
pressure and bringing the rays to a focus on the cathode, where they
would be reflected to the nib