door hung wide. The humming note which had accompanied its opening dwindled to a whisper and died away. Revealed was a tunnel of utter blackness.
Tim Austin released his breath. The sound roused Nellon from the trance which gripped him.
"It's probably controlled by an automatic mechanism. When we shoved against it, we must have set that mechanism in motion."
"I'm going in, Brad," Big Tim said suddenly. "I'm going to see what's inside." He strode impulsively to the door. But at the threshold he stopped and turned and looked at Nellon.
Nellon smiled faintly and nodded. He strode after Big Tim. Together they entered the doorway.
Lights, built into the helmets of their suits, but up to this time unused, were turned on to illuminate the way. The tunnel, they saw, was a rectangular corridor or passageway. It was lined with the same metal as that of the door.
At two intervals down the corridor they found it necessary to squeeze through half-opened doorways. The doors here were of the slide type and seemed to be controlled by machinery as was the one which they had opened to gain entrance to the corridor. But these could not be moved, nor did their efforts awaken any hum of machinery.
"You know," Big Tim remarked, "this arrangement of doors sort of reminds me of an airlock."
"I've noticed the same thing," Nellon responded. "But an airlock—" He shook his head, for this was one of the many things he couldn’t understand.
Soon the corridor came to an end. Nellon and Austin found themselves in a small, square room, each side of which was lined with small glass cubicles or cabinets. In each reposed a transparent sphere with various inexplicable attachments and a compactly folded mass of some strange material.
"Helmets!" Big Tim breathed. "Brad, those are helmets. And unless I'm mistaken the other stuff must be suits of some kind. What have we stumbled onto, anyway?"
Nellon passed a slow, almost-knowing glance about the room, his helmet lights glinting on the glass of the cabinets.
"I've got a crazy idea," he said. "But let that wait until we see more. There's another doorway over there. Let's go on."
THEY went on. There were more corridors, but this time there were rooms opening from them. Each was uniformly alike, filled with the same articles and furnishings. Nothing with which they were familiar had any counterpart here. Everything, from strange, rounded furniture to bizarre clothing, was weirdly alien.
But of the beings who had once inhabited these rooms they found no trace. There were only the garments they had once worn, the chairs in which they had sat. About these clung the ghosts of their presences. Over all was an air of desertion and long neglect.
They entered another section. Here there were rooms as large as halls, spread with queer tables and chairs. One they found to be a library, for on shelves they found large, tablet-like books whose stiff pages were covered with glowing heiroglyphs.
Then they found their first stairway, a succession of small ramps leading to some floor above. They ascended slowly, with the feelings of men entering some new portion of strange and utterly alien world.
Here they found but one, huge room, and this their lights revealed to be perfectly circular. In the center, glow-
