astonishment. The fires outside the windows, the terrific sea of flame about us, had vanished, and we were again flashing on through open space. And now Jor Dahat beside me had seen also, and was rising to his feet.
'We're out of the nebula!' he cried. 'That current must have taken us back up to the surface-back out into space again-'
He was at the window now, gazing eagerly out, while I struggled up in turn. And as I did so I saw awe falling upon his face as he gazed, and heard from him a whispered exclamation of utter astonishment. Then I, too, was on my feet, with Sar Than, and we were at the window beside him, staring forth in turn.
My first impression was of vast space, a colossal reach of space that stretched far away before us, and into which our ship was racing on. And then I saw, with sudden awe and wonder, that this vast space was not the unlimited, unbounded space we were accustomed to, but was limited, was bounded, bounded by a colossal sheet of flowing flame that hemmed it in all directions. Above and below and before and behind us stretched this mighty wall of flame, a gigantic shell of fire that enclosed within itself the vast space in which our cruiser raced, a space large enough to hold within it a dozen solar systems like my own. Stunned, we gazed out into that mighty flame-bounded space, and then I flung out a hand toward it in sudden comprehension.
'We're inside the nebula!' I cried. 'It's hollow! This vast open space lies at its heart, and those currents carried us down into it!'
For I saw now that this was the explanation. Unsuspected by any in the Galaxy the mighty nebula was hollow, its gigantic globe of flaming gas holding at its heart this mighty empty space, a space mighty in extent to our eyes, but small compared to the thickness of the great shell of fire that enclosed it. And down through that fire, that vast ocean of flame, the currents of the nebula had brought us, from its outer surface, down into this great space at its heart of which none had ever dreamed, and into which we had been the first in all the Galaxy to penetrate.
While we gazed across it, stunned, our cruiser was racing on into this vast hollow, away from the wall of flame behind us from which we had just emerged. And now, as we flashed on, Sar Than cried out too and pointed ahead. There, standing out black against the encircling walls of fire in the distance, was a small round spot, a spot that was growing to a black globe as we hurtled on toward it, a globe that hung motionless at the center of this mighty space, here at the nebula's heart. We were racing straight into the great cavity toward it and now there came a low exclamation from Jor Dahat, beside me, as his eyes took in the great globe ahead.
'A planet!' he whispered. 'A planet here-within the nebula!'
My own eyes were fixed upon it, and slowly I nodded, but made no other answer as we flashed on toward the object of our attention, the black sphere ahead. And now as we swept on we saw that it was a sphere of truly titanic dimensions, larger by far than any of the Galaxy's countless worlds, and that as it hung there, at the nebula's heart, it was slowly revolving, spinning, as fast or faster than the nebula itself. Black and mighty it hung there, while all around it, millions of miles from it, there flamed the nebula's encircling fires. On and on we raced toward it, and for all those minutes of flashing flight none of us spoke, and there was no sound in the pilot room but the throbbing drone of the generators below. I think that we all felt instinctively that in the grim, colossal globe ahead lay the answer to what we had come to solve, and as we hurtled on toward it we watched it broadening before us in tense silence.
Larger and larger it was becoming, larger until its great black circle filled half the heavens before us. By then I had decreased our speed to a fraction of its former figure, and as we swept in toward the giant world I lessened it still further. Slowly, ever more slowly we moved, and now were circling above the great black planet, were beginning to drop cautiously down toward it. Eagerly we watched as the mighty world's surface changed from convex to concave, and as we dropped on we saw the needle of our atmosphere-pressure dial moving steadily forward, to show that this strange world had air, at least. Then all else was forgotten as our eyes took in the scene below.
I think that we had all half expected to see some evidence of life and civilization on this strange world, some building or group of buildings, at least. But there was none such. Beneath us lay only a smooth black plain, extending from horizon to horizon, devoid of hill or stream or valley, in so far as we could see, unnaturally smooth and level. And as we dropped nearer, ever nearer, the surprise we felt rapidly intensified, until when at last we hung motionless a hundred feet above the surface of this world exclamations of utter astonishment broke from us. For seen thus near, the surface of this mighty planet was as utterly smooth and level as it had seemed from high above, a black, gleaming plain without an inch-high elevation or depression, an inconceivably strange smooth expanse of black metal, that stretched evenly away in every direction to the horizon, smoothly covering this colossal world.
We looked at each other, a little helplessly, then down again toward the smooth and gleaming surface below. In that surface was no visible opening, no sign of joint or crack, even, nothing but the smooth blank metal. Then with sudden resolution I thrust forward the levers in my hands, sent our cruiser racing low across the surface of the giant, metal sheathed planet, while we gazed intently across that surface in search of any sign that might explain the enigma of its existence. On we sped, while beneath us flashed back the smooth metal plain, mile after endless mile. Then, gazing ahead, my eyes suddenly narrowed and I raised a pointing hand. For there, far ahead, I had glimpsed an opening in the gleaming surface, a round black opening that was resolving itself into a vast circular pit as our cruiser raced on toward it.
Nearer and nearer we flashed toward it, with Sar Than and Jor Dahat beside me gazing forward, their interest as tense as my own. And now we saw that the pit was of gigantic size, its circular mouth all of five miles in diameter, and that from its center there drove up toward the zenith a flickering beam of pale and ghostlike white light, so pale as hardly to be visible, a livid white ray that stabbed straight up toward the fires of the nebula far above. We were very near to the pale beam, now, flashing above the huge pit straight toward it. I had a glimpse of the great pit's perpendicular black metal walls, dropping down for miles into depths inconceivable, of something in those dusky depths that burned like a great white star of light, and then Jor Dahat suddenly uttered a choking cry, flinging an arm out toward the livid ray before us.
'That ray!' he cried. 'It's not light-it's force! The nebula-stop the ship!'
At that cry my hand flew out to the levers, but a moment too late. For before I could throw them back, could slow or stay our progress, we had raced straight into the great pale beam. The next moment there came a terrific crash, as though we had collided with a solid wall; our ship rocked drunkenly in midair for a single instant, and then was whirling crazily downward into the depths of the mighty pit below us.
III
My only memory now of that mad plunge downward is of the pilot room spinning about me, and of the whistling roar of winds outside caused by the speed of our fall. The shock of our collision had apparently silenced our generators, and it was moments before I could struggle up to the controls and make an effort to start them. I jerked open the switches and there came a hum of power from beneath; but the next moment with a jarring, grinding shock our cruiser had met the great pit's floor, flinging us once more to the floor.
For a moment we lay motionless there, and in that moment I became aware of sounds outside, soft rustling sounds that were hardly audible, as of soft-footed creatures moving about. The second shock had again silenced the vibration-mechanism, which I had started the moment before our crash, but I had no doubt that it was only that last-minute action on my part that had slowed our fall enough to save our ship and ourselves from annihilation. Now, staggering to my feet, I reached for the switch of the pilot room's little emergency door, sending it sliding back, admitting a rush of warm, fresh air, and then with my two companions behind me stared dazedly forth.
Our battered cruiser was resting now on the great pit's floor, a vast circular plain of smooth metal five miles in diameter, enclosed on all sides by vertical cliffs of gleaming metal that loomed for miles above us. A dusky twilight reigned here at the great shaft's bottom, but we saw now that that bottom was covered with countless great machines, enigmatic, shining mechanisms that covered the pit's floor completely except for a round clearing at its center, at the edge of which our cruiser rested. From each of the massed machines around us ran a slender tube-connection, and all of these tubes, thousands in number, combined to form a thick black metal cable which led into a huge object at the clearing's center. This was a giant squat cylinder of metal, its height no more than fifty
