it was an antigravity device, but that you denied it."

"Those idiots!" Porter exploded angrily. "Nobody understood what I was
talking about because they wouldn't listen! Antigravity! _Pfui!_ When
they learned how to harness electricity, did they call it
anti-electricity? When they built the first atomic reactor, did they
call it anti-atomic energy? A rocket works against gravity, but they
don't call _that_ antigravity, do they? My device works _with_ gravity,
not against it."

"What sort of device is it?" Elshawe asked.

"I call it the Gravito-Inertial Differential Polarizer," Porter said
importantly.

Elshawe was trying to frame his next question when Porter said: "I know
the name doesn't tell you much, but then, names never do, do they? You
know what a transformer does, but what does the name by itself convey?
Nothing, unless you know what it does in the first place. A cyclotron
cycles something, but what? A broadcaster casts something abroad--what?
And how?"

"I see. And the 'how' and 'what' is your secret, eh?"

"Partly. I can give you a little information, though. Suppose there were
only one planet in all space, and you were standing on its surface.
Could you tell if the planet were spinning or not? And, if so, how fast?
Sure you could; you could measure the so-called centrifugal force. The
same thing goes for a proton or electron or neutron or even a neutrino.
But, if it _is_ spinning, what is the spin relative to? To the particle
itself? That's obvious nonsense. Therefore, what is commonly called
'inertia' is as much a property of so-called 'empty space' as it is a
property of matter. My device simply utilizes spatial inertia by
polarizing it against the matter inertia of the ship, that's all."

"Hm-m-m," said Elshawe. As far as his own knowledge of science went,
that statement made no sense whatever. But the man's manner was
persuasive. Talking to him, Elshawe began to have the feeling that
Porter not only knew what he was talking about, but could actually do
what he said he was going to do.

"What's that?" Porter asked sharply, looking up into the sky.

Elshawe followed his gaze. "That" was a Cadillac aircar coming over a
ridge in the distance, its fans making an ever-louder throaty hum as it
approached. It settled down to an altitude of three feet as it neared,
and floated toward them on its cushion of air. On its side, Elshawe
could see the words, UNITED STATES GOVERNMENT, and beneath that, in
sm