o forth. And enamelled, as it were, on the
outer steel--"

"Cavorite?"

"Yes."

"But how will you get inside?"

"There was a similar problem about a dumpling."

"Yes, I know. But how?"

"That's perfectly easy. An air-tight manhole is all that is needed. That,
of course, will have to be a little complicated; there will have to be a
valve, so that things may be thrown out, if necessary, without much loss
of air."

"Like Jules Verne's thing in _A Trip to the Moon_."

But Cavor was not a reader of fiction.

"I begin to see," I said slowly. "And you could get in and screw yourself
up while the Cavorite was warm, and as soon as it cooled it would become
impervious to gravitation, and off you would fly--"

"At a tangent."

"You would go off in a straight line--" I stopped abruptly. "What is to
prevent the thing travelling in a straight line into space for ever?" I
asked. "You're not safe to get anywhere, and if you do--how will you get
back?"

"I've just thought of that," said Cavor. "That's what I meant when I said
the thing is finished. The inner glass sphere can be air-tight, and,
except for the manhole, continuous, and the steel sphere can be made in
sections, each section capable of rolling up after the fashion of a roller
blind. These can easily be worked by springs, and released and checked by
electricity conveyed by platinum wires fused through the glass. All that
is merely a question of detail. So you see, that except for the thickness
of the blind rollers, the Cavorite exterior of the sphere will consist of
windows or blinds, whichever you like to call them. Well, when all these
windows or blinds are shut, no light, no heat, no gravitation, no radiant
energy of any sort will get at the inside of the sphere, it will fly on
through space in a straight line, as you say. But open a window, imagine
one of the windows open. Then at once any heavy body that chances to be in
that direction will attract us--"

I sat taking it in.

"You see?" he said.

"Oh, I _see_."

"Practically we shall be able to tack about in space just as we wish. Get
attracted by this and that."

"Oh, yes. That's clear enough. Only--"

"Well?"

"I don't quite see what we shall do it for! It's really only jumping off
the world and back again."

"Surely! For example, one might go to the moon."

"And when one got there? What would you find?"

"We should see--Oh! consider the new knowledge."

"Is there air there?"

"There