"Not heat. Warmed air."
Burke went scowling onward. He followed, actually, the only route that was open. Other ways were cut off by doors which refused to open. Sandy, beside him, noted the floor. It was stone like the walls and ceiling. But it was worn. There were slight inequalities in it, beginning a foot or so from the walls. Sandy envisioned thousands of feet moving about these resonant corridors for hundreds or thousands of years in order to wear away the solid stone in this fashion. She felt age about her—incredible age reaching back to time past imagining, while the occupants of this hollow world swarmed about its interior. Doing what?
Burke considered other things. There were the ten-foot metal spheres, ranged by hundreds in what might be a magazine below. There were the squat and ugly metal monsters which seemed definitely menacing to somebody or something. There were the metal frameworks like bunks. There was no rust, here, which could be accounted for if Keller happened to be right and warmed air had been released lately in corridors which before—for ten thousand years or more—had contained only the vacuum of space. And there were those rooms which could be mess-halls.
These items were subject matter for thought. But if what they hinted at was true, there must be other specialized compartments elsewhere. There must be storerooms for food for those who managed the guns—if they were guns—and the spheres, and lived in the bunk-rooms and ate in the mess-halls. There'd be storerooms for equipment and supplies of all sorts. And again, if Keller were right about the air, there must be enormous pressure-tanks which had held the asteroid's atmosphere under high pressure for millennia, only to warm it and release it within the hour so that those who came by ship could use it.
An old phrase occurred to Burke. "A mystery wrapped in an enigma." It applied to these discoveries. Plainly the release of air had been done without the command of any living creature. There could be none here! As plainly, the signals from space had been begun without the interposition of life. The transmitter which still senselessly flung its message to Earth was a robot. The operation of the ship-lock, the warming of air, the lighting of the ship-lock and the corridors—all had been accomplished by machinery, obeying orders given to the transmitter first by some unguessable stimulus.
But why? Other mysteries aside, there had plainly been meticulous preparation for the welcoming of a ship from space. No, not welcoming. Acceptance of a ship from space. Somebody had been expected to respond to those plaintive fluting noises which went wailing through the solar system. Who were those waited-for visitors expected to be? What were they expected to do? For that matter, what was the purpose of the asteroid itself? What had it been built for? At some time or another it must have contained thousands of inhabitants. What were they here for? What became of them? And when the asteroid was left—abandoned—what conceivable situation was to trigger the transmitter to send out urgent calls, and then a directional guiding-signal the instant the call was answered? When Burke's ship came, the asteroid accepted it without question and carried out mechanical operations to make it possible for that ship's crew to roam at will through it. What activated this mechanism of so many eons ago?
The five newly-arrived humans, three men and two girls, trudged along the echoing gallery cut out of the asteroid's heart. Murmurous sounds accompanied them. Once they came to a place where a whispering-gallery effect existed. They heard their footsteps repeated loudly as if the asteroid inhabitants were approaching invisibly, but no one came.
"I don't like this!" Pam said uneasily.
Then her own voice mocked her, and she realized what it was, and giggled nervously. That also was repeated, and sounded like something which seemed to sneer at them. It was unpleasant.
They came to the end of the gallery. There was a stair leading upward. There was nowhere else to go, so Burke started up, Sandy close behind him, and Holmes and Pam behind them. Keller brought up the rear. They climbed, and small noises began to be audible.