"So?"
"It was a mysterious free/ing. The shafts were fairly well heated in those days, and their suit power units were in operation. The stories accumulate embroidery, you know, and, eventually miners wouldn't go into the main shafts in anything but gangs, wouldn't go into the side shafts at all, and the mines shut down."
Lucky nodded. He said, "You'll get the plans for the mines?"
"Right off. And replacements for that inso-suit too."
Preparations proceeded as though for a major expedition. A new inso-suit, replacing the one that had been slashed, was brought and tested, then laid to one side. After all, it would be ordinary space-suits for the dark-side.
The charts were brought and studied. Together with Cook, Lucky sketched out a possible route of exploration, following the main shafts.
Lucky left Bigman to take care of packing the adjunct-units with homogenized food and with water (which could be swallowed while still in the suit), make sure of the charge of the power units and the pressure on the oxygen tanks, inspect the working efficiency of the waste disposal unit and the moisture recirculator.
He himself made a short trip to their ship, the Shooting Starr. He made the trip via the surface, carrying a field pack, the contents of which he did not discuss with Bigman. He returned without it but carrying two small objects that looked like thick belt buckles, slightly curved, in dull-steel finish and centered by a rectangle in glassy red.
"What's that?" asked Bigman.
"Microergometers," said Lucky. "Experimental. You know, like the ergometers on board ship except that those are bolted to the floor."
"What can these things detect?"
"Nothing at a couple of hundred thousand miles like a ship's ergometer, but it can detect atomic power sources at ten miles, maybe. Look, Bigman, you activate it here. See?"
Lucky's thumbnail exerted pressure against a small slit in one side of the mechanism. A sliver of metal moved in, then out, and instantly the red patch on the surface glowed brightly. Lucky turned the small ergometer in this direction and that. In one particular position, the red patch glowed with the energy of a nova.
"That," said Lucky, "is probably the direction of the Dome's power plant. We can adjust the mechanism to zero that out. It's a little tricky." He worked painstakingly on the adjustment of two small controls so smoothly inset as nearly to be invisible.
He smiled as he worked, his engagingly youthful face lighting with pleasure. "You know, Bigman, there isn't a time I visit Uncle Hector but that he doesn't load me up with the Council's latest gadgets. He claims that with the chances you and I are always taking (you know the way he talks) we need them. Sometimes, though, I think he just wants us to act as field-testers for the gadgets. This one, though, may be useful."
"How, Lucky?"
"For one thing, Bigman, if there are Sirians in the mines, they'll have a small atomic power plant. They'll have to. They'll need power for heat, for electrolyzing water, and so on. This ergometer should detect that at ample distance. And for another thing-- "
He fell silent, and Bigman's lips compressed in chagrin. He knew what that silence meant. Lucky had thoughts which later he would claim had been too vague to talk about
"Is one of the ergometers for me?" he asked.
"You bet," said Lucky, tossing one of the ergometers toward him. Bigman snatched it out of the air.
Hanley Cook was waiting for them when they stepped out of their quarters, wearing their suits but with headpieces tucked under their arms.
He said, "I thought I'd lead you as far as the nearest entrance to the shafts."
"Thank you," said Lucky.
It was the tail end of the sleeping period in the Dome. Human beings always established an Earth-like alternation of waking and sleeping, even where there was no day and night to guide them. Lucky had chosen this time on purpose, since he did not want to enter the mines at the head of a curious procession. In this Dr. Peverale had co-operated.
The corridors of the Dome were empty. The lighting was dimmed. And as they walked, a heavy silence seemed to fall about them while the clank of their footsteps sounded even louder.
Cook stopped. "This is Entry Two."
Lucky nodded. "All right. I hope we'll be seeing one another again soon."
"Right."
Cook operated the lock with his usual gloomy gravity, while Lucky and Bigman put on their headpieces, clamping them firmly along the paramagnetic seams. Lucky took his first breath of canned air with what was almost pleasure, he was so accustomed to it.
Lucky first, then Bigman, stepped into the air lock. The wall closed behind them.
Lucky said, "Ready, Bigman?"
"You bet, Lucky." His words rang in Lucky's radio receiver, and his small form was a shadow in the extremely dim light of the lock.
Then the opposing wall opened. They could feel the puff of air escaping into vacuum, and they stepped forward through the opening once again.
A touch at the outer controls and the wall closed behind them again. This time, light was shut off altogether.
Standing in absolute darkness, they found themselves inside the silent and empty mines of Mercury.
7. The Mines of Mercury
The tall man from Earth and his short companion from Mars faced that darkness and marched forward into the bowels of Mercury.
In the radiance of their suit-lights, Bigman looked curiously about at the tunnel, which resembled those he had seen on the Moon. Rounded out smoothly by the use of blasters and disintegrating procedures, it stretched out straight and even. The walls were curved and merged into the rocky ceiling. The oval cross section, slightly flattened above and quite flattened below, made for the greatest structural strength.
Bigman could hear his own steps through the air in his suit. He could sense Lucky's steps only as a small shock of vibration along rock. It was not quite sound, but to a person who had passed as much of his life in vacuum and near-vacuum as had Bigman it was almost as meaningful. He could "hear" the vibration of solid material much as ordinary Earthmen could hear the vibration of air which is called "sound."
Periodically they passed columns of rock which had been left unblasted and which served as buttresses for the layers of rock between the tunnel and the surface. Again this was like the mines on the Moon, except that the buttresses were both thicker and more numerous here, which was reasonable, since Mercury's gravity, small as it was, was two and a half times that of the Moon.
Tunnels branched off the main shaft along which they traveled. Lucky, who seemed in no hurry, paused at each opening in order to compare matters with the chart he carried.
To Bigman, the most melancholy aspect of the mines was the vestiges of one-time human occupancy: the bolts where illumo-plates must once have been attached to keep the corridors blazing with the light of day, the faint markings where paramagnetic relays must once have afforded traction for ore cars, occasional side pockets where rooms or laboratories must have existed, where miners might pause to eat at field kitchens or where samples of ore might be assayed.
All dismantled now, all torn down, only bare rock left.
But Bigman was not the man to brood overlong on such matters. Rather, he grew concerned at the lack of action. He had not come out here merely for the walk.
He said, "Lucky, the ergometer doesn't show a thing."
"I know, Bigman. Cover."
He said it quietly, with no special emphasis, but Bigman knew what it meant. He shoved his radio control to the particular notch which activated a shield for the carrier wave and scrambled the message. It was not regulation equipment on a space-suit, but it was routine for Lucky and Bigman. Bigman had added the scrambler to the radio controls when preparing the suits almost without giving the matter a conscious thought.
Bigman's heart was beating a little faster. When Lucky called for a tight, scrambled beam between the two of them, danger was near. Nearer, at any rate. He said, "What's up, Lucky?"