Tom turned the piston until its flat end was toward the camera. He pressed his forefinger against the center of the circular face, and a small trap door opened.
“This acts as a valve. When it's open, dust can flow through and the piston can sink down the shaft. As soon as it reaches the bottom, the valve will be closed by a signal from above. That will seal off the caisson, and we can start scooping out the dust.
“It sounds very simple, doesn't it? Well, it's not. There are about fifty problems I haven't mentioned. For example, as the caisson is emptied, it will try to float up to the surface with a lift of a good many tons. Chief Engineer Lawrence has worked out an ingenious system of anchors to hold it down.
“You'll realize, of course, that even when this tube has been emptied of dust, there will still be that wedge- shaped gap between its lower end and Selene's roof. How Mister Lawrence proposes to deal with that, I don't know. And please don't send me any more suggestions; we've already had enough half-baked ideas on this program to last a lifetime.
“This-piston gadget—isn't just theory. The engineers here have built and tested it during the last twelve hours, and it's now in action. If I can make any sense of the signals the man's waving at me, I think we're now going over to the Sea of Thirst , to find out what's happening on the raft.”
The temporary studio in the Hotel Roris faded from a million screens; in its place was the picture that, by this time, must have been familiar to most of the human race.
There were now three igloos of assorted sizes on or around the raft; as the sunlight glinted from their reflecting outer surfaces, they looked like giant drops of mercury. One of the dustskis was parked beside the largest dome; the other two were in transit, still shuttling supplies from Port Roris.
Like the mouth of a well, the caisson projected from the Sea. Its rim was only twenty centimeters above the dust, and the opening seemed much too narrow for a man to enter. It would, indeed, have been a very tight fit for anyone wearing a space suit—but the crucial part of this operation would be done without suits.
At regular intervals, a cylindrical grab was disappearing into the well, to be hauled back to the surface a few seconds later by a small but powerful crane. On each withdrawal, the grab would be swung clear of the opening, and would disgorge its contents back into the Sea. For an instant a gray dunce's cap of dust would stand in momentary balance on the level plain; then it would collapse in slow motion, vanishing completely before the next load had emerged from the shaft. It was a conjuring trick being carried out in broad daylight, and it was fascinating to watch. More effectively than a thousand words of description, it told the viewers all that they needed to know about the Sea of Thirst .
The grab was taking longer on its journeys now, as it plunged deeper into the dust. And at last there came the moment when it emerged only half full, and the way to Selene was open-except for that roadblock at the end.
CHAPTER 29
“We're still in very good spirits,” said Pat, into the microphone that had now been lowered down the air shaft. “Of course, we had a bad shock after that second cave-in, when we lost contact with you—but now we're sure you'll soon have us out. We can hear the grab at work, as it scoops up the dust, and it's wonderful to know that help is so close. We'll never forget,” he added, a little awkwardly, “the efforts that so many people have made to help us, and whatever happens we'd like to thank them. All of us are quite sure that everything possible has been done.
“And now I'll hand over the mike, since several of us have messages we want to send. With any luck at all, this will be the last broadcast from Selene.”
As he gave the microphone to Mrs. Williams, he realized that he might have phrased that last remark a little better; it could be interpreted in two ways. But now that rescue was so close at hand, he refused to admit the possibility of further setbacks. They had been through so much that, surely, nothing more would happen to them now.
Yet he knew that the final stage of the operation would be the most difficult, and the most critical, of all. They had discussed it endlessly during the last few hours, ever since Chief Engineer Lawrence had explained his plans to them. There was little else to talk about now that, by common consent, the subject of flying saucers was vetoed.
They could have continued with the book readings, but somehow both Shane and The Orange and the Apple had lost their appeal. No one could concentrate on anything now except the prospects of rescue, and the renewal of life that lay before them when they had rejoined the human race.
From overhead, there was a sudden, heavy thump. That could mean only one thing; the grab had reached the bottom of the shaft, and the caisson was clear of dust. Now it could be coupled to one of the igloos and pumped full of air.
It took more than an hour to complete the connection and make all the necessary tests. The specially modified Mark XIX igloo, with a hole in its floor just large enough to accommodate the protruding end of the caisson, had to be positioned and inflated with the utmost care. The lives of Selene's passengers, and also those of the men attempting to rescue them, might depend upon this air seal.
Not until Chief Engineer Lawrence was thoroughly satisfied did he strip off his space suit and approach that yawning hole. He held a floodlight above the opening and looked down into the shaft, which seemed to dwindle away to infinity. Yet it was just seventeen meters to the bottom; even in this low gravity, an object would take only five seconds to fall that distance.
Lawrence turned to his assistants; each was wearing a space suit, but with the face plate open. If anything went wrong, those plates could be snapped shut in a fraction of a second, and the men inside would probably be safe. But for Lawrence there would be no hope at all—nor for the twenty-two aboard Selene.
“You know exactly what to do,” he said. “If I want to come up in a hurry, all of you pull on the rope ladder together. Any questions?”
There were none; everything had been thoroughly rehearsed. With a nod to his men and a chorus of “Good lucks” in return, Lawrence lowered himself into the shaft.
He let himself fall most of the way, checking his speed from time to time by grabbing at the ladder. On the Moon it was quite safe to do this; well, almost safe. Lawrence had seen men killed because they had forgotten that even this gravity field could accelerate one to a lethal speed in less than ten seconds.
This was like Alice's fall into Wonderland (so much of Carroll might have been inspired by space travel), but there was nothing to see on the way down except the blank concrete wall, so close that Lawrence had to squint to focus upon it. And then, with the slightest of bumps, he had reached the bottom.
He squatted down on the little metal platform, the size and shape of a manhole cover, and examined it carefully. The trapdoor valve that had been open during the piston's descent through the dust was leaking very slightly, and a trickle of gray powder was creeping round the seal. It was nothing to worry about, but Lawrence could not help wondering what would happen if the valve opened under the pressure from beneath. How fast would the dust rise up the shaft, like water in a well? Not as fast, he was quite certain, as he could go up that ladder.
Beneath his feet now, only centimeters away, was the roof of the cruiser, sloping down into the dust at that maddening thirty degrees. His problem was to mate the horizontal end of the shaft with the sloping roof of the cruiser—and to do it so well that the coupling would be dust-tight.
He could see no flaw in the plan; nor did he expect to, for it had been devised by the best engineering brains on Earth and Moon. It even allowed for the possibility that Selene might shift again, by a few centimeters, while he was working here. But theory was one thing—and, as he knew all too well, practice was another.
There were six large thumbscrews spaced around the circumference of the metal disc on which Lawrence was sitting, and he started to turn them one by one, like a drummer tuning his instrument. Connected to the lower side of the platform was a short piece of concertina-like tubing, almost as wide as the caisson, and now folded flat. It formed a flexible coupling large enough for a man to crawl through, and was now slowly opening as Lawrence
