“Exactly.  With no more disturbance than firing a big gun.”

“But what good will that do?”

“I’m going up with it!”

I put down my teacup and stared at him.

“Imagine a sphere,” he explained, “large enough to hold two people and their luggage.  It will be made of steel lined with thick glass; it will contain a proper store of solidified air, concentrated food, water distilling apparatus, and so 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.”