"Mine wasn't casual examination," protested Pan-ner.
Lucky's voice held more than a tinge of bitterness. ''I'm beginning to think that the examination by anyone but an experienced robotics man can be nothing but casual."
They were passing over a drift of snowlike material, glittering in Jupiter light, and Bigman looked down upon it in amazement.
"This thing melts if you look at it," he said. He picked some up in his gauntleted hand, and it melted down and ran off like butter on a stove. He looked back, and where the three had stepped were deep indentations.
Lucky said, "It's not snow, it's frozen ammonia, Bigman. Ammonia melts at a temperature eighty degrees lower than ice does, and the heat radiating from our suits melts it that much faster."
Bigman lunged forward to where the drifts lay deeper, gouging holes wherever he stepped, and shouted, "This is fun."
Lucky called, "Make sure your heater is on if you're going to play in the snow."
"It's on," yelled Bigman, and running down a ridge with long low leaps, he flung himself headlong into a bank. He moved like a diver in slow motion, hit the drifted ammonia, and, for a moment, disappeared. He floundered to his feet.
"It's like diving into a cloud, Lucky. You hear me? Come on, try it. More fun than sand skiing on the moon."
"Later, Bigman," Lucky said. Then he turned to Panner. "For instance, did you try in any way to test any of the men?"
Out of the corner of his eye Lucky could see Bigman plunging into a bank for a second time, and, after a few moments had elapsed, his eyes turned full in that direction. Another moment and he called out anxiously, "Bigman!" Then, more loudly and much more anxiously, "Bigman!"
He started running.
Bigman's voice came, weak and gasping. "Breath… knocked out… hit rock… river down here…"
"Hold on,I'll be with you." Lucky and Panner, too, were devouring space with their strides.
Lucky knew what had happened, of course. The surface temperature of Io was not far removed from the melting point of ammonia. Underneath the ammonia drifts, melting ammonia could be feeding hidden rivers of that foul-smelling, choking substance that existed so copiously on the outer planets and their satellites.
There was the rattle of Bigman's coughing in his ear. "Break in air hose… ammonia getting in… choking."
Lucky reached the hole left by Bigman's diving body and looked down. The ammonia river was plainly visible, bubbling slowly downhill over sharp crags. It must have been against one of those that Bigman's air hose had been damaged.
"Where are you, Bigman?"
And though Bigman answered feebly, "Here," he was nowhere to be seen.
13. Fall!
Lucky jumped recklessly into the exposed river, drifting gently downward under the pull of Io's weak gravity. He was angry at the slowness of his fall, at Bigman for the childish enthusiasms that seized him so suddenly, and-unpredictably-at himself for not having stopped Bigman when he might.
Lucky hit the stream, and ammonia sprayed high in the air, then fell back with surprising quickness. Io's thin atmosphere could not support the small droplets even at low gravity.
There was no sense of buoyancy to the ammonia river. Lucky had not expected any to speak of. Liquid ammonia was less dense than water and had less lifting power. Nor was the force of the current great under Io's weak pull. Had Bigman not damaged his air hose, it would have been only a matter of walking out of the river and through any of the drifts that might have packed it round.
As it was…
Lucky splashed downstream furiously. Somewhere ahead the small Martian must be struggling feebly against the poisonous ammonia. If the break in the hose was large enough, or had grown large enough, to allow liquid ammonia to enter, Lucky would be too late.
He might be too late, already, and his chest constricted and tightened at the thought.
A form streaked past Lucky, burying itself in the powdered ammonia. It disappeared, leaving a tunnel into which ammonia slowly collapsed.
"Panner," Lucky said tentatively.
"Here I am." The engineer's arm fell upon Lucky's shoulder from behind. "That was Mutt. He came running when you yelled. We were both on his wave length."
Together they forged through the ammonia on the track of the dog. They met him, returning.
Lucky cried eagerly, "He's got Bigman."
Bigman's arms feebly enfolded the dog's suit-encased haunches, and though that hampered Mutt's movements, low gravity enabled the dog to make respectable headway through use of shoulder muscles alone.
Even as Lucky bent for Bigman, the little Martian's straining hold relaxed and he fell.
Lucky scooped him up. He wasted no time on investigation or talk. There was only one thing to do. He turned up Bigman's oxygen flow to full capacity, slung him over his shoulders, and ran for the ship. Even allowing for Io's gravity he had never run so recklessly in his life. With such haste did he kick the ground away when coming down from each hurtling, horizontal stride that the effect was almost one of low-level flying.
Panner pumped along in the rear, and Mutt stayed excitedly at Lucky's heels.
Lucky used the communal wave length to alert the others even as he was running and one of the air tights was made ready.
Lucky hurtled inside the air tight, scarcely breaking his stride. The flap closed behind him and the interior flooded with additional air under pressure to make up the loss during the flap's opening.
With flying fingers he unbuckled Bigman's helmet, then more slowly drew off the rest of the suit.
He felt for the heartbeat and, to his relief, found it. The air tight was equipped, of course, with a first-aid kit. He made the necessary injections for general stimulation and waited for warmth and plentiful oxygen to do the rest.
And eventually Bigman's eyes fluttered and focused with difficulty on Lucky. His lips moved and made the word "Lucky," though no sound was involved.
Lucky laughed with relief and finally took the time to remove his own space suit.
On board the Jovian Moon Harry Norrich stopped at the open door of the compartment within which Big-man was completing his recuperation. His unseeing, china-blue eyes were warm with pleasure.
"How's the invalid?"
Bigman struggled up in his bunk and shouted, "Fine! Sands of Mars, I feel great! If it weren't that Lucky wants to keep me down, I'd be up and around."
Lucky grunted his disbelief.
Bigman ignored that. He said, "Hey, let Mutt come in. Good old Mutt! Here, boy, here!"
Mutt, the hold on his harness released, trotted over to Bigman, his tail wagging furiously and his intelligent eyes doing everything but talk a greeting.
Bigman's small arm embraced the dog's neck in a bear hug. "Boy, there's a friend. You heard what he did, Norrich, didn't you?"
"Everyone did," and it was plain to see that Norrich took a great personal pride in his dog's accomplishment.
"I just barely remember it," Bigman said, "before I blacked out altogether. I got that lungful of ammonia and couldn't seem to straighten out. I rolled downhill, just going through the ammonia snow as though it were nothing. Then there was this thing coming at me and I was sure it was Lucky when I heard the sound of something moving. But he knocked enough of the snow off us to let some of the Jupiter light come in and I could just make out it was Mutt. The last thing I remember was grabbing him."
"And a good thing, too," Lucky said. "The extra time that would have been required for me to find you would have been your finish."
Bigman shrugged. "Aw, Lucky, you make such a big deal out of it. Nothing would have happened if I hadn't just caught the hose on a rock and torn it. At that if I had had enough brains to turn up my oxygen pressure, I could have kept the ammonia out. It was just the first lungful that seemed to put me out of kilter. I couldn't think."