air—cold as the void though! Rusty turned a funny blue all over and shivered so violently he could scarcely stand up. But in a minute he sort of recovered and, waving back his would-be rescuers, commenced running and jumping along the rocky cavern floor like a jack-rabbit. Once he slipped on a big lump of platinum—platinum, Smitty!—and when he cussed we could hear him inside the ship through an open port. The air was actually thick enough to carry sounds almost naturally.
"You can't realize how strange it seemed to find air outside the old boat. In five minutes the whole gang of us was cavorting about in that big, dark cavern miles under the surface of the moon. Smitty, you old half-lunged weaklings, you ought to get a whiff of that air. Cold and sharp and sweet as—as I don't know what. Man! You should have seen the red cheeks on us fellows when we climbed back into the bus.
"Eventually we got under way again—all ports opened wide—and headed down what seemed to be the last of the caves. We should have turned back then, only Rusty insisted there might be an opening behind a huge mount of rock at the far side of the place.
"Jupiter! What a thrill we got when we did turn our guide-beam on that pile of stone. Rusty, at the controls, opened his mouth so wide he almost cracked his jaw and his eyes bulged out like balloons. The darned idiot was so stupefied at what we saw that he ran the Meteor IV smack into the cavern wall. Luckily though, we were barely moving; so no damage was done to anything except Rusty himself, and that was done by us.
"Behind this forty-foot mound of debris was a huge black pit, dropping down, down, down. But that in itself was not so marvelous. It was the staircase. Yes, Smitty, old robot, a staircase! Hewn out of the solid rock sides of this shaft was a gigantic flight of steps spiraling around and around, slanting ever downward into the blackness. It was like the threads of some Gargantuan piece of machinery: a comparatively tiny line circling down around the sides of this tremendous shaft.
"Imagine it, Smitty. Down here, eighty miles beneath the moon's surface, in a vast natural chain of caverns, is a giant staircase! Hewn out of the living rock by intelligent animals—human beings, I wonder?—ages ago. Yes, Smitty, this inconceivable staircase must be, judging roughly, some five thousands years old. You see, we—but I'll tell you later, Smitty. If I talk for much longer I'm liable to fill up all your tape. I'll get on with the story.
"What had become of these people? Were some relics of this vanished race farther down the shaft? The stairs must lead some place. We determined to find out where.
WE DIDN'T lose any time dropping our boat down the shaft. The air, now surprizingly dense, fairly screamed as we shot down. Finally we had to slow down considerably because the shaft was beginning to incline from the vertical, gradually assuming a direction that was almost at right-angles with our initial descent.
"Then we sped down this horizontal passageway for a time; yet during all this period we had seen no trace of either our ships or vestiges of the ancient civilisation. But when we cruised around an 'L' bend in the tunnel we immediately doused all our lights and proceeded at caution-speed; for not a hundred years ahead the tunnel opened out into a monstrous cave—a cave whose every surface glowed
