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Silence fell. This time, silence that lasted.
‘Master,’ said the robot, ‘we are here.’
‘Eh?’ Powell snapped out of a semidrowse. ‘Well, get us out of here – out to the surface.’
They found themselves in a tiny substation, empty, airless, ruined. Donovan had inspected a jagged hole in the upper reaches of one of the walls by the light of his pocket flash.
‘Meteorite, do you suppose?’ he had asked.
Powell shrugged. ‘To hell with that. It doesn’t matter. Let’s get out.’
A towering cliff of a black, basaltic rock cut off the sunlight, and the deep night shadow of an airless world surrounded them. Before them, the shadow reached out and ended in knife-edge abruptness into an all-but-unbearable blaze of white light, that glittered from myriad crystals along a rocky ground.
‘Space!’ gasped Donovan. ‘It looks like snow.’ And it did. Powell’s eyes swept the jagged glitter of Mercury to the horizon and winced at the gorgeous brilliance.
‘This must be an unusual area,’ he said. ‘The general albedo of Mercury is low and most of the soil is gray pumice. Something like the Moon, you know. Beautiful, isn’t it?’
He was thankful for the light filters in their visiplates. Beautiful or not, a look at the sunlight through straight glass would have blinded them inside of half a minute.
Donovan was looking at the spring thermometer on his wrist. ‘Holy smokes, the temperature is eighty centigrade!’
Powell checked his own and said: ‘Um-m-m. A little high. Atmosphere, you know.’
‘On Mercury? Are you nuts?’
‘Mercury isn’t really airless,’ explained Powell, in absentminded fashion. He was adjusting the binocular attachments to his visiplate, and the bloated fingers of the insosuit were clumsy at it. ‘There is a thin exhalation that clings to its surface – vapors of the more volatile elements and compounds that are heavy enough for Mercurian gravity to retain. You know: selenium, iodine, mercury, gallium, potassium, bismuth, volatile oxides. The vapors sweep into the shadows and condense, giving up heat. It’s a sort of gigantic still. In fact, if you use your flash, you’ll probably find that the side of the cliff is covered with, say, hoar-sulphur, or maybe quicksilver dew.
‘It doesn’t matter, though. Our suits can stand a measly eighty indefinitely.’
Powell had adjusted the binocular attachments, so that he seemed as eye-stalked as a snail.
Donovan watched tensely. ‘See anything?’
The other did not answer immediately, and when he did, his voice was anxious and thoughtful. ‘There’s a dark spot on the horizon that might be the selenium pool. It’s in the right place. But I don’t see Speedy.’
Powell clambered upward in an instinctive striving for a better view, till he was standing in unsteady fashion upon his robot’s shoulders. Legs straddled wide, eyes straining, he said: ‘I think … I think— Yes, it’s definitely he. He’s coming this way.’
Donovan followed the pointing finger. He had no binoculars, but there was a tiny moving dot, black against the blazing brilliance of the crystalline ground.
‘I see him!’ he yelled. ‘Let’s get going!’
Powell had hopped down into a sitting position on the robot again, and his suited hand slapped against the Gargantuan’s barrel chest. ‘Get going!’
‘Giddy-ap!’ yelled Donovan, and thumped his heels, spur fashion.
The robots started off, the regular thudding of their footsteps silent in the airlessness, for the nonmetallic fabric of the insosuits did not transmit sound. There was only a rhythmic vibration just below the border of actual hearing.
‘Faster!’ yelled Donovan. The rhythm did not change.
‘No use,’ cried Powell, in reply. ‘These junk heaps are only geared to one speed. Do you think they’re equipped with selective flexors?’
They had burst through the shadow, and the sunlight came down in a white-hot wash and poured liquidly about them.
Donovan ducked involuntarily. ‘Wow! Is it imagination or do I feel heat?’
‘You’ll feel more presently,’ was the grim reply. ‘Keep your eye on Speedy.’
Robot SPD 13 was near enough to be seen in detail now. His graceful, streamlined body threw out blazing highlights as he loped with easy speed across the broken ground. His name was derived from his serial initials, of course, but it was apt, nevertheless, for the SPD models were among the fastest robots turned out by the United States Robots and Mechanical Men Corp.
‘Hey, Speedy,’ howled Donovan, and waved a frantic hand.
‘Speedy!’ shouted Powell. ‘Come here!’
The distance between the men and the errant robot was being cut down momentarily – more by the efforts of Speedy than the slow plodding of the fifty-year-old antique mounts of Donovan and Powell.
They were close enough now to notice that Speedy’s gait included a peculiar rolling stagger, a noticeable side-to-side lurch – and then, as Powell waved his hand again and sent maximum juice into his compact head-set radio sender, in preparation for another shout, Speedy looked up and saw them.
Speedy hopped to a halt and remained standing for a moment – with just a tiny, unsteady weave, as though he were swaying in a light wind.
Powell yelled: ‘All right, Speedy! Come here, boy.’
Whereupon Speedy’s robot voice sounded in Powell’s earphones for the first time.
It said: ‘Hot dog, let’s play games. You catch me and I catch you; no love can cut our knife in two. For I’m Little Buttercup, sweet Little Buttercup. Whoops!’ Turning on his heel, he sped off in the direction from which he had come with a speed and fury that kicked up gouts of baked dust.
And his last words as he receded into the distance were, ‘There grew a little flower ’neath a great oak tree,’ followed by a curious metallic clicking that might have been a robotic equivalent of a hiccup.
Donovan said weakly: ‘Where did he pick up the Gilbert and Sullivan? Say, Greg, he … he’s drunk or something.’
‘If you hadn’t told me,’ was the bitter response, ‘I’d never realize it. Let’s get back to the cliff. I’m roasting.’
It was Powell who broke the desperate silence. ‘In the first place,’ he said, ‘Speedy isn’t drunk – not in the human sense – because he’s a robot, and robots don’t get drunk. However, there’s something wrong with him which is the robotic equivalent of drunkenness.’
‘To me, he’s drunk,’ stated Donovan, emphatically, ‘and all I know is that he thinks we’re playing games. And we’re not. It’s a matter of life and very gruesome death.’
‘All right. Don’t hurry me. A robot’s only a robot. Once we find out what’s wrong with him, we can fix it and go on.’
‘Once,’ said Donovan, sourly.
Powell ignored him. ‘Speedy is perfectly adapted to normal Mercurian environment. But this region’ – and his arm swept wide – ‘is definitely abnormal. There’s our clue. Now where do these crystals come from? They might have formed from a slowly cooling liquid; but where would you get liquid so hot that it would cool in Mercury’s sun?’
‘Volcanic action,’ suggested Donovan, instantly, and Powell’s body tensed.
‘Out of the mouths of sucklings,’ he said in a small, strange voice, and remained very still for five minutes.
Then, he said, ‘Listen, Mike, what did you say to Speedy when you sent him after the selenium?’
Donovan was taken aback. ‘Well damn it – I don’t know. I just told him to get it.’
‘Yes, I know. But how? Try to remember the exact words.’
‘I said … uh … I said: “Speedy, we need some selenium. You can get it such-and-such a place. Go get it.” That’s all. What more did you want me to say?’
‘You didn’t put any urgency into the order, did you?’
‘What for? It was pure routine.’
Powell sighed. ‘Well, it can’t be helped now – but we’re in a fine fix.’ He had dismounted from his robot, and was sitting, back against the cliff. Donovan joined him and they linked arms. In the distance the burning sunlight seemed to wait cat-and-mouse for them, and just next to them, the two giant robots were invisible but for the dull red of their photo-electric eyes that stared down at them, unblinking, unwavering and unconcerned.
Unconcerned! As was all this poisonous Mercury, as large in jinx as it was small in size.
Powell’s radio voice was tense in Donovan’s ear: ‘Now, look, let’s start with the three fundamental Rules of Robotics – the three rules that are built most deeply into a robot’s positronic brain.’ In the darkness, his gloved fingers ticked off each point.
‘We have: One, a robot may not injure a human being, or, through inaction, allow a human being to come to harm.’
‘Right!’
‘Two,’ continued Powell, ‘a robot must obey the orders given it by human beings except where such orders would conflict with the First Law.’
‘Right!’
‘And three, a robot must protect its own existence as long as such protection does not conflict with the First or Second Laws.’
‘Right! Now where are we?’
‘Exactly at the explanation. The conflict between the various rules is ironed out by the different positronic potentials in the brain. We’ll say that a robot is walking into danger and knows it. The automatic potential that Rule Three sets up turns him back. But suppose you order him to walk into that danger. In that case, Rule Two sets up a counter-potential higher than the previous one and the robot follows orders at the risks of existence.’
‘Well, I know that. What about it?’
‘Let’s take Speedy’s case. Speedy is one of the latest models, extremely specialized, and as expensive as a battleship. It’s not a thing to be lightly destroyed.’
‘So?’
‘So Rule Three has been strengthened – that was specifically mentioned, by the way, in the advance notices on the SPD models – so that his allergy to danger is unusually high. At the same time, when you sent him out after the selenium, you gave him his order casually and without special emphasis, so that the Rule Two potential set-up was rather weak. Now, hold on; I’m just stating facts.’
‘All right, go ahead. I think I get it.’
‘You see how it works, don’t you? There’s some sort of danger centering at the selenium pool. It increases as he approaches, and a certain distance from it the Rule Three potential, unusually high to start with, exactly balances the Rule Two potential, unusually low to start with.’
Donovan rose to his feet in excitement. ‘And it strikes an equilibrium. I see. Rule Three drives him back and Rule Two drives him forward—’
‘So he follows a circle around the selenium pool, staying on the locus of all points of potential equilibrium. And unless we do something about it, he’ll stay on that circle forever, giving us the good old runaround.’ Then, more thoughtfully: ‘And that, half the way, is what makes him drunk. At potential equilibrium, half the positronic paths of his brain are out of kilter. I’m not a robot specialist, but that seems obvious. Probably he’s lost control of just those parts of his voluntary mechanism that a human drunk has. Ve-e-ery pretty.’
‘But what’s the danger? If we knew what he was running from—’
‘You suggested it. Volcanic action. Somewhere right above the selenium pool is a seepage of gas from the bowels of Mercury. Sulphur dioxide, carbon dioxide – and carbon monoxide. Lots of it – and at this temperature.’
Donovan gulped audibly. ‘Carbon monoxide plus iron gives the volatile iron carbonyl.’
‘And a robot,’ added Powell, ‘is essentially iron.’ Then, grimly: ‘There’s nothing like deduction. We’ve determined everything about our problem but the solution. We can’t get the selenium ourselves. It’s still too far. We can’t send these robot horses, because they can’t go themselves, and they can’t carry us fast enough to keep us from crisping. And we can’t catch Speedy, because the dope thinks we’re playing games, and he can run sixty miles to our four.’
‘If one of us goes,’ began Donovan, tentatively, ‘and comes back cooked, there’ll still be the other.’
‘Yes,’ came the sarcastic reply, ‘it would be a most tender sacrifice – except that a person would be in no condition to give orders before he ever reached the pool, and I don’t think the robots would ever turn back to the cliff without orders. Figure it out! We’re two or three miles from the pool – call it two – the robot travels at four miles an hour; and we can last twenty minutes in our suits. It isn’t only the heat, remember. Solar radiation out here in the ultraviolet and below is poison.’
‘Um-m-m,’ said Donovan, ‘ten minutes short.’
‘As good as an eternity. And another thing. In order for Rule Three potential to have stopped Speedy where it did, there must be an appreciable amount of carbon monoxide in the metal-vapor atmosphere – and there must be an appreciable corrosive action atmosphere. He’s been out hours now – and how do we know when a knee joint, for instance, won’t be thrown out of kilter and keel him over. It’s not only a question of thinking – we’ve got to think fast!’
Deep, dark, dank, dismal silence!
Donovan broke it, voice trembling in an effort to keep itself emotionless. He said: ‘As long as we can’t increase Rule Two potential by giving further orders, how about working the other way? If we increase the danger, we increase Rule Three potential and drive him backward.’
Powell’s visiplate had turned toward him in a silent question.
‘You see,’ came the cautious explanation, ‘all we need to do to drive him out of his rut is to increase the concentration of carbon monoxide in his vicinity. Well, back at the Station there’s a complete analytical laboratory.’
‘Naturally,’ assented Powell. ‘It’s a Mining Station.’
‘All right. There must be pounds of oxalic acid for calcium precipitations.’
‘Holy space! Mike, you’re a genius.’
‘So-so,’ admitted Donovan, modestly. ‘It’s just a case of remembering that oxalic acid on heating decomposes into carbon dioxide, water, and good old carbon monoxide. College chem, you know.’
Powell was on his feet and had attracted the attention of one of the monster robots by the simple expedient of pounding the machine’s thigh.
‘Hey,’ he shouted, ‘can you throw?’
‘Master?’
‘Never mind.’ Powell damned the robot’s molasses-slow brain. He scrabbled up a jagged brick-size rock. ‘Take this,’ he said, ‘and hit the patch of bluish crystals just across that crooked fissure. You see it?’
Donovan pulled at his shoulder. ‘Too far, Greg. It’s almost half a mile off.’
‘Quiet,’ replied Powell. ‘It’s a case of Mercurian gravity and a steel throwing arm. Watch, will you?’
The robot’s eyes were measuring the distance with machinely accurate stereoscopy. His arm adjusted itself to the weight of the missile and drew back. In the darkness, the robot’s motions went unseen, but there was a sudden thumping sound as he shifted his weight, and seconds later the rock flew blackly into the sunlight. There was no air resistance to slow it down, nor wind to turn it aside – and when it hit the ground it threw up crystals precisely in the center of the ‘blue patch’.
Powell yelled happily and shouted, ‘Let’s go back after the oxalic acid, Mike.’
And as they plunged into the ruined substation on the way back to the tunnels, Donovan said grimly: ‘Speedy’s been hanging about on this side of the selenium pool, ever since we chased after him. Did you see him?’
‘Yes.’
‘I guess he wants to play games. Well, we’ll play him games!’
They were back hours later, with three-liter jars of the white chemical and a pair of long faces. The photo-cell banks were deteriorating more rapidly than had seemed likely. The two steered their robots into the sunlight and toward the waiting Speedy in silence and with grim purpose.
