of rays which, if they are generated in space at all, are beyond
our present reach. The zone of force is necessary to shield certain
items of equipment from ether vibrations; as any such vibration inside
the controlling fields of force renders observation or control of the
higher orders of rays impossible."

"Hm ... m, I see--I'm learning something," Seaton replied cordially.
"Just as the higher-powered a radio set is, the more perfect must be its
shielding?"

"Yes. Just as a trace of any gas will destroy the usefulness of your
most sensitive vacuum tubes, and just as imperfect shielding will allow
interfering waves to enter sensitive electrical apparatus--in that same
fashion will even the slightest ether vibration interfere with the
operation of the extremely sensitive fields and lenses of force which
must be used in controlling forces of the higher orders."

"You haven't tested the theory of the fourth order yet, have you?"

"No, but that is unnecessary. The theory of the fourth order is not
really theory at all--it is mathematical fact. Although we have never
been able to generate them, we know exactly the forces you use in your
ship of space, and we can tell you of some thousands of others more or
less similar and also highly useful forces which you have not yet
discovered, but are allowing to go to waste. We know exactly what they
are, how to liberate and control them, and how to use them. In fact, in
the work which we are to begin today, we shall use but little ordinary
power: almost all our work will be done by fourth-order forces,
liberated from copper by means of the Rovolon you have given me. But
here we are at my laboratory. You already know that the best way to
learn is by doing, and we shall begin at once."

* * * * *

The flier alighted upon a lawn quite similar to the one before the
observatory of Orlon, and the scientist led his Earthly guest through
the main entrance of the imposing structure of vari-colored marble and
gleaming metal and into the vast, glass-lined room that was his
laboratory. Great benches lined the walls, and there were hundreds of
dials, meters, tubes, transformers and other instruments, whose uses
Seaton could not even guess.

Rovol first donned a suit of transparent, flexible material, of a deep
golden color, instructing Seaton to do the same; explaining that much of
the work would be with dangerous frequencies and with high pressures,
and th