a level steel platform, but seemed to be
composed of many lenticular sections of dull blue alloy.

"We are standing upon the upper lookout lenses, aren't we?" asked the
girl. "Is that perfectly all right?"

"Sure. They're so hard that nothing can scratch them, and of course
Roeser's Rays go right through our bodies, or any ordinary substance,
like a bullet through a hole in a Swiss cheese. Even those lenses
wouldn't deflect them if they weren't solid fields of force."

As he spoke, one of the ultra-lights flashed around in a short, quick
arc, and the girl saw that instead of the fierce glare she had expected,
it emitted only a soft violet light. Nevertheless she dodged
involuntarily and Stevens touched her arm reassuringly.

"All x, Miss Newton--they're as harmless as mice. They hardly ever have
to swing past the vertical, and even if one shines right through you you
can look it right in the eye as long as you want to--it can't hurt you
a bit."

"No ultra-violet at all?"

"None whatever. Just a color--one of the many remaining crudities of our
ultra-light vision. A lot of good men are studying this thing of direct
vision, though, and it won't be long before we have a system that will
really work."

"I think it's all perfectly wonderful!" she breathed. "Just think of
traveling in comfort through empty space, and of actually seeing through
seamless steel walls, without even a sign of a window! How can such
things be possible?"

"I'll have to go pretty well back," he warned, "and any adequate
explanation is bound to be fairly deep wading in spots. How technical
can you stand it?"

"I can go down with you middling deep--I took a lot of general science,
and physics through advanced mechanics. Of course, I didn't get into any
such highly specialized stuff as sub-electronics or Roeser's Rays, but
if you start drowning me, I'll yell."

"That's fine--you can get the idea all x, with that to go on. Let's sit
down here on this girder. Roeser didn't do it all, by any means, even
though he got credit for it--he merely helped the Martians do it. The
whole thing started, of course, when Goddard shot his first rocket to
the moon, and was intensified when Roeser so perfected his short waves
that signals were exchanged with Mars--signals that neither side could
make any sense out of. Goddard's pupils and followers made bigger and
better rockets, and finally got one that could land safely upon Mars.
Roeser, who was a mighty