against the Setaur. The Setaur possessed an automatic sighter, since its photoelectric eyes were hooked up directly to the laser and it could instantly fire at whatever lay in the center of its field of vision. Theirs, on the other hand, was a quaint sort of sighter, probably from an old cosmonautical range finder; it had been tested in this way, namely, that before leaving Luna they took a few shots at some rocks on the horizon. The rocks had been large, the distance no greater than a mile, and even so they hit the mark only on the fourth try. And here, to make matters worse, you had lunar conditions to cope with, because a laser ray was visible as a brilliant streak only in a diffusing medium, e.g. an earthlike atmosphere; but in empty space a beam of light, regardless how powerful, was invisible until it hit some material obstacle. Therefore on Earth you could shoot a laser much the way you shot tracer bullets, being guided by their observable line of flight. Without a sighter a laser on the Moon was of no practical value. Pirx didn’t keep this from McCork; he told him when only a couple of minutes separated them from the hypothetical danger zone.
“I didn’t think of that,” said the engineer, then added with a smile:
“Why did you tell me?”
“To free you of illusions,” replied Pirx, not looking up from the double eyepiece of his periscope. It had foam- rubber cushions, but he felt sure that he would be going around with black eyes for the longest time (assuming, of course, he came out of this alive). “And also, to explain why we’re carrying that stuff in the back.”
“The cylinders?” asked McCork. “I saw you taking them from the storeroom. What’s in them?”
“Ammonia, chlorine and some hydrocarbons or other,” said Pirx. “I thought they might come in handy…”
“A gas-smoke screen?” ventured the engineer.
“No, what I had in mind was some way of aiming. If there’s no atmosphere, we create one, at least temporarily…”
“I’m afraid there won’t be time for that.”
“Perhaps not… I took it along just in case. Against one that is insane, insane measures are often best…”
They fell silent, for the transporter had begun to lurch like a drunk; the stabilizers whined and squealed, sounding as if any minute the oil in them would begin to boil. They hurtled down an incline strewn with sharp boulders. The opposite slope gleamed, all white with pumice.
“You know what worries me most?” resumed Pirx when the heaving let up a little; for he had grown strangely talkative. “Not the Setaur—not at all… It’s those transporters from Construction. If just one of them takes us for the Setaur and starts blasting away with its laser, things’ll get lively.”
“I see you’ve thought of everything,” muttered the engineer. The cadet, sitting beside the radio operator, leaned across the back of his seat and handed Pirx a scrawled radiogram, barely legible.
“We have entered the danger zone at relay twenty, so far nothing, stop, Strzibor, end of transmission,” Pirx read aloud. “Well, we’ll soon have to put our helmets on too…”
The machine slowed a little, climbing a slope. Pirx noticed that he could no longer see the neighbor on his left—only the right transporter was moving like a dim blot up the bank. He ordered the left machine to be raised by radio, but there was no answer.
“We have begun to separate,” he said calmly. “I thought that would happen. Can’t we push the antenna up a little higher? No? Too bad.”
By now they were at the summit of a gentle rise. From over the horizon, at a distance of less than two hundred kilometers, emerged, full in the sun, the sawtooth ridge of the crater Toricelli, sharply outlined against the black background of the sky. They had the plain of the Sea of Tranquillity all but behind them now. Deep tectonic rifts appeared, frozen slabs of magma jutted here and there from under the debris, and over these the transporter crawled with difficulty, heaving up first like a boat on a wave, then dropping heavily down, as though it were about to plunge head over heels into some unknown cavity. Pirx caught sight of the mast of the next relay, glanced quickly at the celluloid map card pressed to his knees, and ordered everyone to fasten their helmets. From now on they would be able to communicate only by inside telephone. The transporter managed to shake even more violently than before—Pirx’s head wobbled around in its helmet like the kernel of a nut inside an empty shell.
When they drove down the slope to lower ground, the saw of Toricelli disappeared, blocked out by nearer elevations; almost at the same time they lost their right neighbor. For a few minutes more they heard its call signal, then that was distorted by the waves bouncing off the sheets of rock, and complete radio silence followed. It was extremely awkward trying to look through the periscope with a helmet on; Pirx thought he would either crack his viewplate or smash the eyepiece. He did what he could to keep his eyes on the field of vision at all times, though it shifted totally with each lurch of the machine and was strewn with endless boulders. The jumble of pitch-black shadow and dazzlingly bright surfaces of stone made his eyes swim. Suddenly a small orange flame leaped up in the darkness of the far sky, flickered, dwindled, disappeared. A second flash, a little stronger. Pirx shouted: “Attention everyone! I see explosions!”—and feverishly turned the crank of the periscope, reading the azimuth off the scale etched onto the lenses.
“We’re changing course!” he howled. “Forty-seven point eight, full speed ahead!”
The order really applied to a cosmic vessel, but the driver understood it all the same; the plates and every joint of the transporter gave a shudder as the machine wheeled around practically in place and surged forward. Pirx got up off his seat, its tossing was pulling his head away from the eyepiece. Another flash—this time red-violet, a fan-shaped burst of flame. But the source of those flashes or explosions lay beyond the field of vision, hidden by the ridge they were climbing.
“Attention everyone!” said Pirx. “Prepare your individual lasers! Dr. McCork, please go to the hatch. When I give the word or in case of a hit, you’ll open it! Driver! Decrease velocity!…”
The elevation up which the machine clambered rose from the desert like the shank of some moon monster, half-sunken in debris; the rock in fact resembled, by its smoothness, a polished skeleton or giant skull; Pirx ordered the driver to go to the top. The treads began to chatter, like steel over glass. “Hold it!” yelled Pirx, and the transporter, coming to a sudden halt, dipped nosedown towards the rock, swayed, the stabilizers groaning with the strain, and stopped.
Pirx looked into a shallow basin enclosed on two sides by radially spreading, tapered embankments of old magma flows; two-thirds of the wide depression lay in glaring sun, a third was covered by a shroud of absolute black. On that velvet darkness there shone, like a weird jewel, fading ruby-red, the ripped-open skeleton of a vehicle. Only the driver saw it besides Pirx, for the armor flaps of the windows had been lowered. Pirx, to tell the truth, didn’t know what to do. “A transporter,” he thought. “Where is the front of it? Coming from the south? Probably from the construction group, then. But who got it, the Setaur? And I’m standing here in full view, like an idiot—we have to conceal ourselves. But where are all the other transporters? Theirs and mine?”
“I have something!” shouted the radiotelegraph man. He connected his receiver to the inside circuit, so that everyone could hear the signals in their helmets.
“Aximo-portable talus! A wall with encystation—repetition from the headland unnecessary—the access at an azimuth of—multicrystalline metamorphism…” the voice filled Pirx’s earphones, delivering the words clearly, in a monotone, with no intonation whatever.
“It’s him!” he yelled. “The Setaur! Hello, radio! Get a fix on that, quickly! We need a fix! For God’s sake! While it’s still sending!” He roared till he was deafened by his own shouts amplified in the closed space of the helmet; not waiting for the telegraph operator to snap out of it, he leaped, head bent, to the top of the turret, seized the double handgrip of the heavy laser and began turning it along with the turret, his eyes already at the sighter. Meanwhile inside his helmet that low, almost sorrowful, steady voice droned on:
“Heavily bihedrous achromatism viscosity—undecorticated segments without repeated anticlinal interpolations”—and the senseless gabble seemed to weaken.
“Where’s that fix, damn it?!!”
Pirx, keeping his eyes glued to the sighter, heard a faint clatter—McCork had run up front, shoved aside the operator, there was a sound of scuffling…
Suddenly in his earphones he heard the calm voice of the cyberneticist:
“Azimuth 39.9 … 40.0 … 40.1 … 40.2…”
“It’s moving!” Pirx realized. The turret had to be turned by crank; he nearly dislocated his arm, he cranked so hard. The numbers moved at a creep. The red line passed the forty mark.
Suddenly the voice of the Setaur rose to a drawn-out screech and broke off. At that same moment Pirx pressed the trigger and half a kilometer down, right at the line between light and shadow, a rock spouted fire
