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  “I know there aren’t,” the voice then went on, responding to the words they could not hear, “but it’s only two or three miles, I’d say. Two to the spur and not much farther to where I could see the other side. Enough of the way is in shade so I could make it in a suit easily enough. I can’t see calling back either of the Darkside tractors. Their work is just as important as the rest — anyway, Eileen is probably out of range. She hasn’t answered yet.”

  Another pause.

  “That’s true. Still, it would mean sacrificing that set of seismic records — no, wait. We could go out later for those. And Mel could take his own weather measures on the later trip. There’s plenty of time!”

  Pause, longer this time.

  “You’re right, of course. I just wanted to get an early look at this volcano, if it is one. We’ll let the others finish their runs, and when you get back you can check the thing from the other side yourself. If it is blocking your way there’s time to find an alternate route. We could be doing that from the maps in the meantime, just in case.”

  Zaino looked at his companion.

  “Isn’t that just my luck!” he exclaimed. “I jump at the first chance to get away from being bored to death. The minute I’m safely away, the only interesting thing of the whole operation happens — back at the ship!”

  “Who asked to come on this trip?”

  “Oh, I’m not blaming anyone but myself. If I’d stayed back there the volcano would have popped out here somewhere, or else waited until we were gone.”

  “If it is a volcano. Dr. Burkett didn’t seem quite sure.” “No, and I’ll bet a nickel she’s suiting up right now to go out and see. I hope she comes back with something while we’re still near enough to hear about it.”

  Hargedon shrugged. “I suppose it was also just your luck that sent you on a Darkside trip? You know the radio stuff. You knew we couldn’t reach as far this way with the radios. Didn’t you think of that in advance?”

  “I didn’t think of it, any more than you would have. It was bad luck, but I’m not grousing about it. Let’s get on with this job.” Hargedon nodded with approval, and possibly with some surprise, and the tractor hummed on its way.

  The darkness deepened around the patches of lava shown by the driving lights; the sky darkened toward a midnight hue, with stars showing ever brighter through it; and radio reception from the Albireo began to get spotty. Gas density at the low ion layer was high enough so that recombination of molecules with their radiation-freed electrons was rapid. Only occasional streamers of ionized gas reached far over Darkside. As these thinned out, so did radio reception. Camille Burkett’s next broadcast came through very poorly.

  There was enough in it, however, to seize the attention of the two men in the tractor.

  She was saying: “—real all right, and dangerous. It’s the. . thing I ever saw. . kinds of lava from what looks like. . same vent. There’s high viscosity stuff building a spatter cone to end all spatter cones, and some very thin fluid from somewhere at the bottom. The flow has already blocked the valley used by the Brightside routes and is coming along it. A new return route will have to be found for the tractors that. . was spreading fast when I saw it. I can’t tell how much will come. But unless it stops there’s nothing at all to keep the flow away from, the ship. It isn’t coming fast, but it’s coming. I’d advise all tractors to turn back. Captain Rowson reminds me that only one takeoff is possible. If we leave this site, we’re committed to leaving Mercury. Arnie and Ren, do you hear me?”

  Zaino responded at once. “We got most of it, Doctor. Do you really think the ship is in danger?”

  “I don’t know. I can only say that if this flow continues the ship will have to leave, because this area will sooner or later be covered. I can’t guess how likely. . check further to get some sort of estimate. It’s different from any Earthly lava source — maybe you heard — should try to get Eileen and Eric back, too. I can’t raise them. I suppose they’re well out from under the ion layer by now. Maybe you’re close enough to them to catch them with diffracted waves. Try, anyway. Whether you can raise them or not you’d better start back yourself.”

  Hargedon cut in at this point. “What does Dr. Mardikian say about that? We still have most of the seismometers on this route to visit.”

  “I think Captain Rowson has the deciding word here, but if it helps your decision Dr. Mardikian has already started back. He hasn’t finished his route, either. So hop back here, Ren. And Arnie, put that technical skill you haven’t had to use yet to work raising Eileen and Eric.”

  “What I can do, I will,” replied Zaino, “but you’d better tape a recall message and keep it going out on — let’s see band F.”

  “All right. be ready to check the volcano as soon as you get back. How long?”

  “Seven hours — maybe six and a half,” replied Hargedon. “We have to be careful.”

  “Very well. Stay outside when you arrive; I’ll want to go right out in the tractor to get a closer look.” She cut off.

  “And that came through clearly enough!” remarked Hargedon as he swung the tractor around. “I’ve been awake for fourteen hours, driving off and on for ten of them. I’m about to drive for another six; and then I’m to stand by for more.”

  “Would you like me to do some of the driving?” asked Zaino.

  “I guess you’ll have to, whether I like it or not,” was the rather lukewarm reply. “I’ll keep on for a while though — until we’re back in better light. You get at your radio job.”

  Zaino tried. Hour after hour he juggled from one band to another. Once he had Hargedon stop while he went out to attach a makeshift antenna which, he hoped, would change his output from broadcast to some sort of beam; after this he kept probing the sky with the “beam,” first listening to the Albireo’s broadcast in an effort to find projecting wisps of ionosphere and then, whenever he thought he had one, switching on his transmitter and driving his own message at it.

  Not once did he complain about lack of equipment or remark how much better he could do once he was back at the ship.

  Hargedon’s silence began to carry an undercurrent of approval not usual in people who spent much time with Zaino. The technician made no further reference to the suggestion of switching drivers. They came in sight of the Albireo and doubled the chasm with Hargedon still at the wheel, Zaino still at his radio and both of them still uncertain whether any of the calls had gotten through.

  Both had to admit, even before they could see the ship, that Burkett had had a right to be impressed.

  The smoke column showed starkly against the sky, blowing back over the tractor and blocking the sunlight which would otherwise have glared into the driver’s eyes. Fine particles fell from it in a steady shower; looking back, the men could see tracks left by their vehicle in the deposit which had already fallen.

  As they approached the ship the dark pillar grew denser and narrower, while the particles raining from it became coarser. In some places the ash was drifting into fairly deep piles, giving Hargedon some anxiety about possible concealed cracks. The last part of the trip, along the edge of the great chasm and around its end, was really dangerous, cracks running from its sides were definitely spreading. The two men reached the Albireo later than Hargedon had promised, and found Burkett waiting impatiently with a pile of apparatus beside her.

  She didn’t wait for them to get out before starting to organize.

  “There isn’t much here. We’ll take off just enough of what you’re carrying to make room for this. No — wait. I’ll have to check some of your equipment; I’m going to need one of Milt Schlossberg’s gadgets, I think, so leave that on. We’ll take—”

  “Excuse me, Doctor,” cut in Hargedon. “Our suits need servicing, or at least mine will if you want me to drive you. Perhaps Arnie can help you load for a while, if you don’t think it’s too important for him to get at the radio—”

  “Of course. Excuse me. I should have had someone out here to h
elp me with this. You two go on in. Ren, please get back as soon as you can. I can do the work here; none of this stuff is very heavy.”

  Zaino hesitated as he swung out of the cab. True, there wasn’t too much to be moved, and it wasn’t very heavy in Mercury’s gravity, and he really should be at the radio; but the thirty-nine-year-old mineralogist was a middle-aged lady by his standards, and shouldn’t be allowed to carry heavy packages. .

  “Get along, Arnie!” the middle-aged lady interrupted this train of thought. “Eric and Eileen are getting farther away and harder to reach every second you dawdle!”

  He got, though he couldn’t help looking northeast as he went rather than where he was going.

  The towering menace in that direction would have claimed anyone’s attention. The pillar of sable ash was rising straighter, as though the wind were having less effect on it. An equally black cone had risen into sight beyond Northeast Spur — a cone that must have grown to some two thousand feet in roughly ten hours. It had far steeper sides than the cinder mounds near it; it couldn’t be made of the same loose ash. Perhaps it consisted of half-melted particles which were fusing together as they fell — that might be what Burkett had meant by “spatter-cone.” Still, if that were the case, the material fountaining from the cone’s top should be lighting the plain with its incandescence rather than casting an inky shadow for its entire height.

  Well, that was a problem for the geologists; Zaino climbed aboard and settled to his task.

  The trouble was that he could do very little more here than he could in the tractor. He could have improvised longer-wave transmitting coils whose radiations would have diffracted a little more effectively beyond the horizon, but the receiver on the missing vehicle would not have detected them. He had more power at his disposal, but could only beam it into empty space with his better antennae. He had better equipment for locating any projecting wisps of charged gas which might reflect his waves, but he was already located under a solid roof of the stuff — the Albireo was technically on Brightside. Bouncing his beam from this layer still didn’t give him the range he needed, as he had found both by calculation and trial.

  What he really needed was a relay satellite. The target was simply too far around Mercury’s sharp curve by now for anything less.

  Zaino’s final gesture was to set his transmission beam on the lowest frequency the tractor would pick up, aim it as close to the vehicle’s direction as he could calculate from map and itinerary and set the recorded return message going. He told Rowson as much.

  “Can’t think of anything else?” the captain asked. “Well neither can I, but of course it’s not my field. I’d give a year’s pay if I could. How long before they should be back in range?”

  “About four days. A hundred hours, give or take a few. They’ll be heading back anyway by that time.”

  “Of course. Well, keep trying.”

  “I am — or rather, the equipment is. I don’t see what else I can do unless a really bright idea should suddenly sprout. Is there anywhere else I could be useful? I’m as likely to have ideas working as just sitting.”

  “We can keep you busy, all right. But how about taking a transmitter up one of those mountains? That would get your wave farther.”

  “Not as far as it’s going already. I’m bouncing it off the ion layer, which is higher than any mountain we’ve seen on Mercury even if it’s nowhere near as high as Earth’s.”

  “Hmph. All right.”

  “I could help Ren and Dr. Burkett, I could hang on outside the tractor—”

  “They’ve already gone. You’d better call them, though, and keep a log of what they do.”

  “All right,” Zaino turned back to his board and with no trouble raised the tractor carrying Hargedon and the mineralogist. The latter had been trying to call the Albireo and had some acid comments about radio operators who slept on the job.

  “There’s only one of me, and I’ve been trying to get the Darkside team,” he pointed out. “Have you found anything new about this lava flood?”

  “Flow, not flood,” corrected the professional automatically. “We’re not in sight of it yet. We’ve just rounded the corner that takes us out of your sight. It’s over a mile yet, and a couple of more corners, before we get to the spot where I left it. Of course, it will be closer than that by now. It was spreading at perhaps a hundred yards an hour then. That’s one figure we must refine. Of course, I’ll try to get samples, too. I wish there were some way to get samples of the central cone. The whole thing is the queerest volcano I’ve ever heard of. Have you gotten Eileen started back?”

  “Not as far as I can tell. As with your cone samples, there are practical difficulties,” replied Zaino. “I haven’t quit yet, though.”

  “I should think not. If some of us were paid by the idea we’d be pretty poor, but the perspiration part of genius is open to all of us.”

  “You mean I should charge a bonus for getting this call through?” retorted the operator.

  Whatever Burkett’s reply to this might have been was never learned; her attention was diverted at that point.

  “We’ve just come in sight of the flow. It’s about five hundred yards ahead. We’ll get as close as seems safe, and I’ll try to make sure whether it’s really lava or just mud.”

  “Mud? Is that possible? I thought there wasn’t — couldn’t be — any water on this planet!”

  “It is, and there probably isn’t. The liquid phase of mud doesn’t have to be water, even though it usually is on Earth. Here, for example, it might conceivably be sulfur.”

  “But if it’s just mud, it wouldn’t hurt the ship, would it?”

  “Probably not.”

  “Then why all this fuss about getting the tractors back in a hurry?”

  The voice which answered reminded him of another lady in his past, who had kept him after school for drawing pictures in math class.

  “Because in my judgment the flow is far more likely to be lava than mud, and if I must be wrong I’d rather my error were one that left us alive. I have no time at the moment to explain the basis of my judgment. I will be reporting our activities quite steadily from now on, and would prefer that you not interrupt unless a serious emergency demands it, or you get a call from Eileen.

  “We are about three hundred yards away now. The front is moving about as fast as before, which suggests that the flow is coming only along this valley. It’s only three or four feet high, so viscosity is very low or density very high. Probably the former, considering where we are. It’s as black as the smoke column.”

  “Not glowing?” cut in Zaino thoughtlessly.

  “Black, I said. Temperature will be easier to measure when we get closer. The front is nearly straight across the valley, with just a few lobes projecting ten or twelve yards and one notch where a small spine is being surrounded. By the way, I trust you’re taping all this?” Again Zaino was reminded of the afternoon after school.

  “Yes, Ma’am,” he replied. “On my one and only monitor tape.”

  “Very well. We’re stopping near the middle of the valley one hundred yards from the front. I am getting out, and will walk as close as I can with a sampler and a radiometer. I assume that the radio equipment will continue to relay my suit broadcast back to you.” Zaino cringed a little, certain as he was that the tractor’s electronic apparatus was in perfect order.

  It struck him that Dr. Burkett was being more snappish than usual. It never crossed his mind that the woman might be afraid.

  “Ren, don’t get any closer with the tractor unless I call. I’ll get a set of temperature readings as soon as I’m close enough. Then I’ll try to get a sample. Then I’ll come back with that to the tractor, leave it and the radiometer and get the markers to set out.”

  “Couldn’t I be putting out the markers while you get the sample, Doctor!”

  “You could, but I’d rather you stayed at the wheel.” Hargedon made no answer, and Burkett resumed her description for the record.<
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  “I’m walking toward the front, a good deal faster than it’s flowing toward me. I am now about twenty yards away, and am going to take a set of radiation-temperature measures.” A brief pause. “Readings coming. Nine sixty. Nine eighty. Nine ninety — that’s from the bottom edge near the spine that’s being surrounded. Nine eighty-five—” The voice droned on until about two dozen readings had been taped. Then, “I’m going closer now. The sampler is just a ladle on a twelve-foot handle we improvised, so I’ll have to get that close. The stuff is moving slowly; there should be no trouble. I’m in reach now. The lava is very liquid; there’s no trouble getting the sampler in — or out again — it’s not very dense, either. I’m heading back toward the tractor now. No, Ren, don’t come to meet me.”

  There was a minute of silence, while Zaino pictured the space-suited figure with its awkwardly long burden, walking away from the creeping menace to the relative safety of the tractor. “It’s frozen solid already; we needn’t worry about spilling. The temperature is about — five eighty. Give me the markers, please.”

  Another pause, shorter this time. Zaino wondered how much of that could be laid to a faster walk without the ladle and how much to the lessening distance between flow and tractor. “I’m tossing the first marker close to the edge — it’s landed less than a foot from the lava. They’re all on a light cord at ten-foot intervals; I’m paying out the cord as I go back to the tractor. Now we’ll stand by and time the arrival at each marker as well as we can.”

  “How close are you to the main cone?” asked Zaino. “Not close enough to see its base, I’m afraid. Or to get a sample of it, which is worse. We — goodness, what was that?’

  Zaino had just time to ask, “What was what?” when he found out.

  For a moment, he thought that the Albireo had been flung bodily into the air. Then he decided that the great metal pillar had merely fallen over. Finally he realized that the ship was still erect, but the ground under it had just tried to leave.