contact with the ground, it would not take long to heat up dangerously. Also, with the comet now whipping closer and closer to perihelion, there was already an annoyingly large gap in the photographic record.
Back in the tunnel, Ries improvised another set of shields for the camera and its operator, and checked the one he had used to see how much snow remained in it. There was some, but discouragingly little. He placed his helmet against that of Donegan and spoke — the radios were useless in the Sun's static.
“You can't go out until we get more snow for this thing, and you'll have to come back every few minutes for a refill. I'd do the photography, but you know better than I what has to be taken. I hope you can make out what you need to see through the sixty-five hundred filter in the shield I made for the finder. I'll be back.”
He started back down the tunnel, but at the second turn met another suited figure coming out — with a large bag of snow. He recognized Pawlak by the number on the suit, since the face of the occupant was invisible behind the filter. Ries took the bag and gestured his thanks; Pawlak indicated that he would go back and bring more, and started on this errand. Ries reappeared at the camera soon enough to surprise his companion, but the physicist wasted no time in questions. The two men restuffed the shields with snow, and Donegan went back to the tunnel mouth to do his job.
Through the filter, the angry surface of the sun blazed a fiery orange. Features were clear enough, though not always easy to interpret. Individual “rice grains” were clearly visible; a small spot, badly foreshortened, showed far to one side. By moving his head as far as the shield allowed, the observer could see well away from the camera's line of sight; doing this, of course, blued the sun as the ray path difference between the reflecting layers in the filter was shortened. He could not tell exactly what wavelength he was using at any given angle, but he quickly learned to make use of the rather crude “tuning” that angle change afforded. He began shooting, first the spot and its neighborhood, altering the camera filter wavelength regularly as he did so. Then he found something that might have been a calcium flocculus and took a series around it; then feature after feature caught his eye, and he shot and shot, trying to get each field through the full wavelength range of the camera at about fifty Angstrom intervals plus definite lengths which he knew should be there — the various series lines of hydrogen and of neutral and ionized helium particularly, though he did not neglect such metals as calcium and sodium.
He was distracted by a pull on his armored foot; Ries had come up, inadequately protected by the single remaining sheet of “parasol,” to warn him to recharge his own shield. Reluctantly he did so, grudging the time. Ries packed snow against the feet of the camera mounting while Donegan stuffed it between the foil layers of his shield as rapidly as his space-suited hands could work. The moment this was done he headed back to the tunnel mouth, now not so far away as it had been, and resumed operations.
They must have been almost exactly at perihelion then. Donegan neither knew nor cared. He knew that the camera held film enough to let him take one picture a second for about ninety minutes, and he intended to use all of it if he could. He simply scanned the sun as completely as his eyesight, the protecting filter, and his own knowledge permitted, and recorded as completely as possible everything even slightly out of the ordinary that he saw. He knew that many instruments were still at work in the ship, even though many were not, and he knew that some of the devices on the comet's surface would function — or should function — automatically even though remote control was gone; and he intended that there should be a complete record in pictures of everything which might be responsible for whatever those machines recorded. He did a good job.
Not too many — in fact, as time went on, too few — yards below him Ries also worked. If being an instrument maintenance specialist involved moving snow, and in this part of the universe it seemed to involve little else, then he would move snow. He had plenty of it; Pawlak kept bringing more and more bags of the stuff. Also, on his second trip, the engineer produced a lengthy coil of wire; and at the first opportunity Ries fastened one end of this to Donegan's ankle. It served two purposes — it was no longer necessary to go out to let the fellow know by physical contact that his time was getting short, and it let the observer get back to work more quickly. Since he was belayed to Ries, who could brace himself against the tunnel walls beyond the bend, there was no worry of going back to the surface too rapidly and being unable to stop.
Ries kept busy. No one ever knew whether he did it silently or not, since the radios were unavailable. It was generally taken for granted that he grumbled as usual, and he may very well have done just that, or even surpassed himself. Hanging weightless in a white-glowing tunnel, trying to read a watch through the heaviest solar filter made for space helmets, holding one end of a line whose other end was keeping a man and a fantastically valuable camera from drifting away and becoming part of the solar corona, all the while trying to organize a number of large plastic sacks of pulverized frozen water, ammonia, and methane which persistently gathered around him would have driven a more self-controlled man than Ries to bad language.
Of course, Donegan didn't map the whole surface. This would take quite a while, using a camera with a half-degree field on a surface over ninety-five degrees across, even when the surface in question is partly hidden by the local horizon. It was made even more impossible by their rate of motion; parabolic velocity at a distance of five hundred eighty thousand miles from Sol's center is just about three hundred thirty miles per second, and that produced noticeable relative motion even against a background a hundred and fifty thousand miles away. Features were disappearing below the solar horizon, sometimes, before Donegan could get around to them. Even Ries could think of no solution to this difficulty, when the physicist complained of it on one of his trips for more snow.
At this point, the sun's apparent motion in latitude was more rapid than that in longitude — the comet was changing its direction from the sun more rapidly than it was rotating. The resultant motion across the sky was a little hard to predict, but the physicist knew that the center of the solar disk would set permanently at the latitude of the tunnel mouth an hour and three-quarters after perihelion. The angular size of the disk being what it was, there would be some observing after that, but how much depended on what might be called the local time of day, and he had not attempted to figure that out. He simply observed and photographed, except when Ries dragged him forcibly back to get his shield recharged.
Gradually the gigantic disk shrank. It never was far above the local horizon, so there was always something with which to compare it, and the shrinking could be noticed. Also, Ries could tell as time went on that there was a little more snow left in Donegan's shield each time it came back for refilling. Evidently they were past the worst.
But the sun had taken its toll. The mouth of the tunnel was much closer to the ship than it had been; several times Ries had been forced back to another section of tunnel with his snow bags, and each resumption of observation by Donegan had involved a shorter trip than before to the surface. Ries, Donegan, and Pawlak were the only members of the expedition to know just how far the evaporation was progressing, since the echo-sounder had been wrecked by the magnetic field; they were never sure afterward whether this was good or not. Those inside were sustained, presumably, by their faith in mathematics. For the physicists this was adequate, but it might not have been for Ries if he had been with them. In any case, he didn't worry much about the fate of the comet after perihelion had been passed; he had too many other troubles, even though his activity had quickly become routine. This left him free to complain— strictly to himself.
Donegan was furious when he finally realized that the sun was going to set at his observing station while it was still close enough to photograph. Like Ries, however, he had no way of expressing his annoyance so that anyone could hear him; and as it turned out, it would have been wasted breath. Observation was cut even shorter by something else.
They had been driven down to what had been originally the third bend in the tunnel, and at this point the passage ran horizontally for a time. Pawlak had just come to the other end of this straight stretch with what he hoped would be his last load of snow when something settled gently through its roof between him and Ries. He leaped toward it, dropping his burden, and discovered that it was one of the instruments which had been on the surface. Its silver cover was slightly corroded, and the feet of its mounting badly so. Apparently its reflecting powers had been lowered by the surface change, and it was absorbing more energy than an equivalent area of comet; so its temperature had gone up accordingly, and it had melted its way below the rest of the surface.
Low as the sun was, it was shining into the hole left by the instrument; evidently the pit it had made was very broad and shallow. Pawlak made his way around the piece of gear and up to Ries, whose attention was directed elsewhere, and reported what had happened. The instrument man looked back down the tunnel and began to haul in on the line attached to Donegan. The physicist was furious when he arrived, and the fact became evident when the three helmets were brought together.
“What in blazes is going on here?” he fulminated. “You can't make me believe my shield had boiled dry again — I haven't been out five minutes, and the loads are lasting longer now. We're losing the sun, you idiot; I can't come back because someone has a brainstorm or can't read a watch…'
