The picture was still clear and bright, though there was little to see, for there were now few changes in the ground structure. The pressure was already rising to a thousand atmospheres; soon it would be impossible for any cavity to remain open, for the rock itself would begin to flow. Mile after mile I sank, but only a pale mist floated on the screen, broken sometimes when echoes were returned from pockets or lodes of denser material. They became fewer and fewer as the depth increased—or else they were now so small that they could no longer be seen.
The scale of the picture was, of course, continually expanding. It was now many miles from side to side, and I felt like an airman looking down upon an unbroken cloud ceiling from an enormous height. For a moment a sense of vertigo seized me as I thought of the abyss into which I was gazing. I do not think that the world will ever seem quite solid to me again.
At a depth of nearly ten miles I stopped and looked at the Professor. There had been no alteration for some time, and I knew that the rock must now be compressed into a featureless, homogeneous mass. I did a quick mental calculation and shuddered as I realized that the pressure must be at least thirty tons to the square inch. The scanner was revolving very slowly now, for the feeble echoes were taking many seconds to struggle back from the depths.
“Well, Professor,” I said, “I congratulate you. It’s a wonderful achievement. But we seem to have reached the core now. I don’t suppose there’ll be any change from here to the centre.”
He smiled a little wryly. “Go on,” he said. “You haven’t finished yet.”
There was something in his voice that puzzled and alarmed me. I looked at him intently for a moment; his features were just visible in the blue-green glow of the cathode-ray tube.
“How far down can this thing go?” I asked, as the interminable descent started again.
“Fifteen miles,” he said shortly. I wondered how he knew, for the last feature I had seen at all clearly was only eight miles down. But I continued the long fall through the rock, the scanner turning more and more slowly now, until it took almost five minutes to make a complete revolution. Behind me I could hear the Professor breathing heavily, and once the back of my chair gave a crack as his fingers gripped it.
Then, suddenly, very faint markings began to reappear on the screen. I leaned forward eagerly, wondering if this was the first glimpse of the world’s iron core. With agonizing slowness the scanner turned through a right angle, then another. And then…
I leaped suddenly out of my chair, cried “My God!” and turned to face the Professor. Only once before in my life had I received such an intellectual shock—fifteen years ago, when I had accidentally turned on the radio and heard the fall of the first atomic bomb. That had been unexpected, but this was inconceivable. For on the screen had appeared a grid of faint lines, crossing and recrossing to form a perfectly symmetrical lattice.
I know that I said nothing for many minutes, for the scanner made a complete revolution while I stood frozen with surprise. Then the Professor spoke in a soft, unnaturally calm voice.
“I wanted you to see it for yourself before I said anything. That picture is now thirty miles in diameter, and those squares are two or three miles on a side. You’ll notice that the vertical lines converge and the horizontal ones are bent into arcs. We’re looking at part of an enormous structure of concentric rings; the centre must lie many miles to the north, probably in the region of Cambridge. How much further it extends in the other direction we can only guess.”
“But what is it, for heaven’s sake?”
“Well, it’s clearly artificial.”
“That’s ridiculous! Fifteen miles down!”
The Professor pointed to the screen again. “God knows I’ve done my best,” he said, “but I can’t convince myself that Nature could make anything like that.”
I had nothing to say, and presently he continued: “I discovered it three days ago, when I was trying to find the maximum range of the equipment. I can go deeper than this, and I rather think that the structure we can see is so dense that it won’t transmit my radiations any further.
“I’ve tried a dozen theories, but in the end I keep returning to one. We know that the pressure down there must be eight or nine thousand atmospheres, and the temperature must be high enough to melt rock. But normal matter is still almost empty space. Suppose that there is life down there—not organic life, of course, but life based on partially condensed matter, matter in which the electron shells are few or altogether missing. Do you see what I mean? To such creatures, even the rock fifteen miles down would offer no more resistance than water—and we and all our world would be as tenuous as ghosts.”
“Then that thing we can see—”
“Is a city, or its equivalent. You’ve seen its size, so you can judge for yourself the civilization that must have built it. All the world we know—our oceans and continents and mountains—is nothing more than a film of mist surrounding something beyond our comprehension.”
Neither of us said anything for a while. I remember feeling a foolish surprise at being one of the first men in the world to learn the appalling truth; for somehow I never doubted that it was the truth. And I wondered how the rest of humanity would react when the revelation came.
Presently I broke into the silence. “If you’re right,” I said, “why have they—whatever they are—never made contact with us?”
The Professor looked at me rather pityingly. “We think we’re good engineers,” he said, “but how could we reach them? Besides, I’m not at all sure that there haven’t been contacts. Think of all the underground creatures and the mythology—trolls and kobolds and the rest. No, it’s quite impossible—I take it back. Still, the idea is rather suggestive.”
All the while the pattern on the screen had never changed: the dim network still glowed there, challenging our sanity. I tried to imagine streets and buildings and the creatures going among them, creatures who could make their way through the incandescent rock as a fish swims through water. It was fantastic… and then I remembered the incredibly narrow range of temperatures and pressures under which the human race exists. We, not they, were the freaks, for almost all the matter in the universe is at temperatures of thousands or even millions of degrees.
“Well,” I said lamely, “what do we do now?”
The Professor leaned forward eagerly. “First we must learn a great deal more, and we must keep this an absolute secret until we are sure of the facts. Can you imagine the panic there would be if this information leaked out? Of course, the truth’s inevitable sooner or later; but we may be able to break it slowly.
“You’ll realize that the geological surveying side of my work is now utterly unimportant. The first thing we have to do is to build a chain of stations to find the extent of the structure. I visualize them at ten-mile intervals towards the north, but I’d like to build the first one somewhere in South London to see how extensive the thing is. The whole job will have to be kept as secret as the building of the first radar chain in the late thirties.
“At the same time, I’m going to push up my transmitter power again. I hope to be able to beam the output much more narrowly, and so greatly increase the energy concentration. But this will involve all sorts of mechanical difficulties, and I’ll need more assistance.”