"In a little while," I said, "these plants will be as high as we are.
Suppose--suppose after all-- Is it certain? How do you know that stuff
_is_ air? It may be nitrogen--it may be carbonic acid even!"

"That's easy," he said, and set about proving it. He produced a big piece
of crumpled paper from the bale, lit it, and thrust it hastily through the
man-hole valve. I bent forward and peered down through the thick glass for
its appearance outside, that little flame on whose evidence depended so
much!

I saw the paper drop out and lie lightly upon the snow. The pink flame of
its burning vanished. For an instant it seemed to be extinguished. And
then I saw a little blue tongue upon the edge of it that trembled, and
crept, and spread!

Quietly the whole sheet, save where it lay in immediate contact with the
snow, charred and shrivelled and sent up a quivering thread of smoke.
There was no doubt left to me; the atmosphere of the moon was either pure
oxygen or air, and capable therefore--unless its tenuity was excessive--of
supporting our alien life. We might emerge--and live!

I sat down with my legs on either side of the manhole and prepared to
unscrew it, but Cavor stopped me. "There is first a little precaution,"
he said. He pointed out that although it was certainly an oxygenated
atmosphere outside, it might still be so rarefied as to cause us grave
injury. He reminded me of mountain sickness, and of the bleeding that
often afflicts aeronauts who have ascended too swiftly, and he spent some
time in the preparation of a sickly-tasting drink which he insisted on my
sharing. It made me feel a little numb, but otherwise had no effect on me.
Then he permitted me to begin unscrewing.