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“How far down in this damned planet do you think the stuff might be, Cliff?”

Val Morrison asked the question. He sat folded up outside the tent wall, short pipe crackling between his big teeth. Six feet four, thin as a knifeblade, with a face like a pickaxe, he was possibly the toughest man in the whole outfit. He sat regarding Cliff Anderson now through his tiny, merry little dark eyes.

“Lord knows!” The chief engineer rubbed his big, stubby chin. “Doesn’t matter much, anyway; these Martian guys who went before us did a whole lot of chiseling. We’re down two thousand miles already—but no sign of anilum so far. Soon we’ll hit Mars’ core. Mebbe we’ll find something before then.”

“Yeah—we hope . . .” Val drew at his pipe dubiously.

The sudden blare of signal sirens came from the depths. The whining din echoed through the reaches of the tunnels and shafts. The voices of the men at the head of the main shaft came forth in a murmur of sound.

Immediately Cliff and Val were on their feet, glancing at each other.

“Guess they must have hit something vital,” Val said briefly.

He started to move forward as he spoke, Cliff beside him. At the pit top Cliff elbowed his way through the men.

“What’s wrong below? What’s happened?”

The radio operator in contact with below glanced up.

“Number 4 unit operating in underground cavern has encountered a steel wall, sir. Want your advice . . .”

“Steel wall? Down there!” Cliff looked his amazement. “But how the devil did—”

“Oh be damned to conjectures; let’s go,” Val snapped, and strode forward into the waiting shaft cage. He waited until Cliff had joined him, then threw in the switches.

For several minutes they dropped steadily down through the miles of shafting thrust deep into the planet’s bowels. At last they touched bottom, flung back the grille, then hurried over to the group of engineers gathered round their enormous boring machine. It had stopped before a massive rotunda of gray metal stretching up into the cavern ceiling and on either side as far as the eye could see.

Richardson, the engineer in charge, nodded to the barrier as Cliff came up.

“Thought it was anilum^[1] at first, Cliff, but our tests show it is steel of sorts. All in one piece; been flowed together by some skilled process. No sign of a join. Thought you’d better see it before we tried blasting it through. Might be something dangerous on the other side.”

Cliff surveyed it keenly. “Such as?”

“You never know. Maybe molten lava: even conserved water supplies. Might be anything. The Martians sure didn’t mean it escaping whatever it is . . .”

Val drew at his noisy pipe. “Might even be Martian life behind it,” he murmured. “I’m not fooling,” he went on, seeing Cliff’s doubting look. “After all, I figure the Martians must have gone somewhere, and we’ve seen no trace of life in the upper or surface regions since we landed on this hell-fired planet.”

Cliff tugged out his ray gun and fired it experimentally at the barrier. The metal sizzled and liquefied under the heat. He nodded curtly.

“O.K., start blasting it through. But take it easy and use a small radius. If there’s anything dangerous released we’ll have time to get clear anyway.”

The big engineer gave the order. With Val beside him, Cliff mounted to the borer’s flat deck and stood among the crew. In the belly of the ship’s control room the men set about their tasks. The powerful tractors moved. A needle-pointed spear of incandescent heat stabbed the barrier and began to drive through it like a white-hot needle through a slab of butter. The air began to reek of heated metals and electric discharges.

At the end of a half-hour the reaction instruments showed the boring was finished. Immediately cooling radiations were forced through the barrier and searchlights were swung onto the foot-wide hole.

Staring into it the engineers could see nothing but darkness.

“There’s air anyway,” Val said, frowning. “Distinct draft blowing through.”

“That might be the air blowing right through the planet from the other side,” Cliff mused. “Doesn’t seem attenuated enough though . . .”

He shrugged and turned to the borers.

“All right; finish the job,” he said. “Use full range this time and plow right through.”

This time the beam incorporated an area wide enough to permit of the entire borer machine following it through. As before it took it thirty minutes to nose its juggernaut way through the wall, which was all of twenty-five to thirty feet in thickness. Once beyond the barrier engineers stood sniffing the stale, musty air and gazing round in the glare of the searchlights.

They were within a colossal artificially bored cavern, filled with an extraordinary number of gray metal balls dotted about in various directions. Some were large and some small, but all were bolted and riveted immovably to tripod stands of metal. Right and left they went, round the natural curve of the cavern out of sight. In the cavern’s center was yet another ball of metal, gray like the smaller balls, and apparently a kind of master ball. The distance to the major ball was perhaps two miles. How far the cavern itself really extended was lost in darkness.

The air seemed to be coming from a source in the cavern hidden by the major ball.

Cliff climbed down from the borer and went to the nearest ball, stood looking at it perplexedly. At last he turned to the others and held up his hand for silence.

In a moment it was clear that the little ball was whirring mysteriously like a spring uncoiling.

“Machinery!” Richardson ejaculated.

Silence fell on the party again as there came a new sound through the heavy silence—a solemn, deliberate ticking like that of a giant grandfather clock.

It went on steadily and Cliff consulted his watch.

“Something is ticking at exactly three second intervals,” he proclaimed finally. “And it has only just started. . . . Looks like we have stumbled onto something, boys.”

Val said slowly, “The ticking comes from that giant ball there. Let’s take a look at it.”

They mounted the borer again and drove forward the intervening distance. The progress of the journey made the ticking all the more audible, until by the time they had reached the giant ball itself it was a solemn reverberation that boomed along the floor.

Tick . . . Tock. Tick . . . Tock.

“Time bomb?” Vale suggested laconically.

“Quit clowning,” Cliff snapped impatiently. “It’s pretty plain we started the works going by coming in here. Nothing happened until we went over to look at that smaller ball. Somehow I don’t like it. There’s a deliberation about that ticking that’s kind of ominous.”

“Yeah . . .” Val meditated. He said, “Suppose before we start forming opinions we look around a bit? This air mystery, for instance . . .”

At the rear of the giant ball they discovered the reason for the air supply and its un-Martian density. A titanic vent sunken into the floor, and presumably communicating by a complicated shafting system to the other side of Mars itself—right through to the surface—was covered with a massive lid of machinery, the unit itself being housed inside a transparent case. The components were working visibly in the midst of a mass of thin gluey substance.

As the thin air streamed up the giant shaft it passed into one giant valve in the machinery, went through an amplifying process by which heavier air pressure was added, and was then expelled by a piston system at the other side of the machine, a massive pipe being driven through the tough outer casing. The thing was virtually the mechanical heart of Mars pumping out good air from thin, spent currents.

“The Martians were damn good engineers, anyway,” Val commented. “But just why did they need to give air to this cavern in particular when there is only a lot of balls in it that don’t need air to work in . . .?”

“Unless,” Cliff mused, “they wanted intelligent life to come into this cavern and have a look round in order to start the machinery going. The air would invite anybody inside—as it did us. I’ll bet, when we broke through the wall, we completed a circuit that started the air pump working.”

Val’s pipe crackled. “Say, maybe you’ve got something. Anyway, we can check up on that by examining the wall later. What we’ve got to do right now is find out what makes these balls tick.”

He tugged out his gun and fired it experimentally at a corner of the heart’s transparent casing. The beam simply glanced off. Val stared blankly.

“By all the saints, it’s anilum!” he gasped. “Moulded anilum, at that. Ray guns will never penetrate this! It takes a temperature of something like 15,000° C. to melt it.

“Everything in this cave’s made of anilum,” said Cliff.

The engineers glanced at each other, then with one accord they looked at the monster ball. Within it something was still ticking solemnly at regular three-second intervals.

“Say, something’s just occurred to me,” Val said presently. “Is it possible that we’re right at the core of Mars and that this giant metal ball is natural? Or at least it was natural until it changed into unthinkably hard anilum.^[2]”

“So what?” Cliff’s brows were knitted.

“If the Martian engineers found a way to hollow out its center, which is quite conceivable, they might have put something inside it. From the stuff out of the center they manufactured all these other little balls. We’d probably find by mathematics that the material used in these little balls equals the extracted mass from inside the larger one. In plain words, pressure changed nickle iron into anilum, but Martian science was clever enough to enable the Martians to find out how to bore through it and hollow it out. The seam of anilum which Fredison found seems to show that that seam was ejected volcanically, proving conclusively that it was from the bowels of Mars.”

“Which might explain why we can’t find anilum on Earth,” Cliff mused. “So far our Earth has not ejected any of its deep baser material; only the upper molten metals. Deep down there will be anilum, but we shall never find it until Earth is as riddled with passages to its core as Mars now is. Yes, Val, I think you’ve got something . . . But I’ll be damned if I understand the Martian purpose.”

The puzzled silence that fell on the group was broken suddenly by a hoarse scream from Richardson. He had wandered from the others to inspect the next steel ball. Simultaneously with his scream everybody present saw a light wink momentarily with blinding brilliance high up in the lofty ceiling of the chasm. Richardson, dead in line with it, collapsed his length on the cavern floor.

“My God!” Cliff ejaculated, startled—then he rushed forward with the others beside him.

That they were too late was obvious the moment they turned the engineer over. His face was charred to ashes, the upper part of his neck and chest were burned away horribly.

Cliff raised a grim face and stared round on the now inscrutable roof and its galleries of rock and pumice stone.

“Something mechanical that killed him,” he whispered, standing up again. “Boys, we’re facing something deadly around here. It’s got to be located . . .”

He stood watching bitterly as the unfortunate Richardson was carried to the borer. The solemn ticking of the giant ball followed the stunned party.

Once back at the upper levels in the base camp Cliff summoned his engineering chiefs from their different tasks and put the position to them.

“. . . and so we face a mystery,” he concluded. “Down there in the core of Mars is a mechanical system of destruction controlled by God knows what. It’s taken Richardson. We know neither the extent nor the nature of the thing we’re fighting—but we do know that we are going to stop it. We’ve found anilum too, though not exactly in the way we had hoped. That makes searching in other parts of this planet unnecessary. What you have got to do is get every available flame gun machine and transport it down to the lower cavern. We’re going to try and liquefy those anilum balls, and the big one which ticks. We have one or two portable furnaces and since the balls are on tripods we can shove the furnaces under them.

“You, Townshend, are our chief scientist.” Cliff looked at the squat, broad-shouldered man standing before him. “You’ll go to work to try and figure out why those balls tick, and what they are supposed to be. It won’t be easy, and you may never solve the mystery—but there’s no harm in trying.”

“I’ve got the instruments; maybe I’ll find something.” Townshend nodded his gray head.

“We others will go to work to find out exactly what it was that struck Richardson down,” Cliff concluded grimly. “Sparks, you stay here in case we have to radio to Earth for help.”

He turned to the door of the base with the others beside him. Then they paused and glanced at each other quickly at a sudden alien sound. It was a noise such as they had never heard before on Mars, a noise other than that of their own work.

From remote distances came clanging concussions, the rattle of metal flanges slamming against each other and followed by the sharper note of locks snapping into position. Four times it was repeated. Twice from high over their heads and twice from below their feet. Then all was quiet again.

“You know something,” Val said in the ensuing calm, “I dare to think that that was the locks to the outer surface closing! There are four of them you know . . .”

Puzzled, loath to believe the startling possibility of Val’s assertion, Cliff led the way to the shaft cage. Once the men were gathered—fifty in all—the descent began. Ten minutes later the entire party was back in the cavern.

The searchlights on the borer were switched on and Cliff gave brief instructions. Then while three men remained to watch the searchlights and guide them according to orders, the others went to work to examine the rocky walls of the place inch by inch. Ladders were set up against the approximate spot where the light had burned out Richardson’s life.

Val and Cliff chose this particular task as their own especial duty. It took them some fifteen minutes of searching to discover a ball of anilum, only a small one, imbedded in the rock. In the center of the ball was curiously faceted lens.

“Looks like a glorified limelight,” Val said, scratching his head. “Not a chance of moving it. Only thing to do is to avoid it.”

“Yeah, I guess you’re right—”

Cliff broke off with a start and turned round with dangerous speed on the ladder at a sudden wild scream from the opposite side of the cavern. He and Val were just in time to see part of the floor crack suddenly up the center in so neat a chasm that it was obviously mechanical. The floor simply fell apart in one complete seam—but into it dropped nearly thirty of the workers gathered in a bunch to inspect the giant ball. Their screams, mingled with the grinding roar of the floor’s parting, filled the giant cavern with hideous commotion.

Cliff started to say something, then changed his mind. He scrambled down the ladder at top speed with Val tumbling after him. With the other workmen and scattered engineers they raced across in long leaps to the opening—but before they reached it it began to close with invincible power like the jaws of a mammoth press. The agonized cries from below lapsed abruptly into silence. With a mighty clang the metal floor linked up again, leaving a line so thin it was almost indetectable.

Cliff wiped his sweating face and looked around in bewilderment on his comrades’ horrified faces.

“I don’t begin to understand it,” he almost whispered. “This is unthinkable! Ghastly! Thirty of them trapped down there and then crushed to death. . . . We’ve got to stop this if it’s the last thing we ever do! You realize that, all of you?” he nearly shouted.

“Yeah, sure. Take it easy. It wasn’t your fault.” Val’s voice was gruff with sympathy.

“Not my fault, perhaps, but I’m head of the Expedition and responsible for everybody here. Try to think how I feel . . .” Cliff knelt down and stared at the closed jaws of the floor. He got up with a hopeless look in his eyes. “No possible chance of doing anything until we smash open these damned anilum balls!” he blazed. “Get dynamite, titanite, every damn thing! We’ll blast this cavern wide open if we go to hell with it!”

Cliff twisted round sharply as Benson shouted hoarsely, “The air conditioning machine has stopped!”

“We’ve got our portable unit,” Val said, relighting his pipe with feigned calmness. No time now to let panic gain a foothold. “Better get it, just in case we have trouble getting free.”

Benson departed, and with him the men who were to bring the explosives. Cliff paced up and down swiftly, impatiently, watched by the other engineers. Most of them turned to look presently at the crack in the floor which had so ruthlessly swallowed up most of the party. They glanced uncertainly, furtively, around them, conscious of unseen but diabolical forces waiting to swallow them.

Suddenly Townshend said, “Say, we might get to know what’s in these little balls—and the big one too for that matter—by X-ray. If it will penetrate anilum, and there’s no reason why not, we might be able to get a photograph of what’s going on. Guess I’ll go to work on that angle.”

He departed actively, but in two minutes he returned suddenly. His face, usually so ruddy, had gone pale.

“Come and take a look . . .” he whispered.

At the words Cliff stopped pacing and raised a haggard face. He moved immediately with the others at his side. Outside the cavern entrance leading to the elevator shaft they stopped appalled. The workmen who had left, and Benson, were lying stretched motionless in a jumble of human figures not ten yards from the elevator.

His heart pounding, Cliff went warily forward in case the same fate overtook him. Nothing happened, however . . .

He needed only to look at Benson’s ashy, contorted visage to know the condition of the others. They were dead, every man of them. Cliff turned bitter eyes up to the walls and ceilings, and though he could see nothing unusual he could guess the cause of the annihilation. From somewhere a clockwork sniping ray had done its deadly work.^[3]

“We’ll go up and fetch the explosives down for ourselves,” he stated quietly. “Only way to be rid of the bodies is to incinerate them. Seems brutal, but there’s no time for sentiment . . . We’ll be next if we don’t act fast. Let’s go.”

The six of them, all that remained except the radio operator above, moved charily toward the elevator and clambered inside. Cliff threw the switches, then as the cage began to rise, he gave a sudden shout. A blinding ray winked momentarily from the opposite wall of the cavern. A resonant twang caused him to glance up just in time to see the steel hawser split through four of its six strands.

“Look out!” he yelled hoarsely, and jammed the switch out of contact. The next instant the remaining strands parted and the cage dropped down the hundred foot length to the floor. Thanks to the lesser gravity the impact was lessened slightly, but just the same it was mighty enough to smash the bottom of the cage through.

Edwards and Saunders vanished in a smother of splintering timber and crumbling elevator walls. Cliff found himself thrown clear with Val on top of him. Townshend, Morton, and Gilby scrambled out with nothing worse than cuts and bruises.

Immediately they turned to help their buried colleagues, hurling aside timber and metal supports. Half way through the task Cliff called a halt.

“No use, boys; we’re only wasting time. Take a look . . .”

He indicated the two hands unearthed from the wreckage. There were no indications of pulse beats on either wrist.

Cliff switched on his wrist radio and hooked the tiny phone in his ear. He half expected a dead silence from Sparks as he gave the call signal, but Sparks’ voice answered at once.

“What happened, Cliff? Cage give way? I was just figuring out what to do . . .”

“Only one thing you can do right now and that’s drop a rope. And hurry!”

“O.K. Hang on; I’ll fix a winch. And when you come up I’ve some news that’ll interest you.”

Cliff switched off.

“It’s suicide!” Val protested. “If we cross the same point in the shaft again how do we know we won’t be wiped out?”

Cliff shrugged. “Have to chance it. We can’t stick here. If it took a whole cage to block the ray it’s possible a small thing like a human body might get past without intercepting it.”

In a few minutes a cradle and rope came down the vast length of the shaft.

“I’ll go first,” Cliff said, slipping into the cradle. “If anything goes wrong, prepare to catch me!”

He gave two tugs and hung on tightly as the cradle began to rise. Nothing untoward happened. He sailed swiftly up past the danger point—higher and higher to the topmost levels. Sparks joined him anxiously at the winch top.

“How many others down there, Cliff?” he asked anxiously.

“Four,” he answered with grim significance.

“The others coming up later, I suppose?”

“I only wish they were,” Cliff muttered, and seeing the operator’s amazed look he went on, “They’re dead, Sparks—killed by mystic powers down in the bowels of this ungodly world. Tell you more afterwards. Get the others up first . . .”

Three times more the cradle was lowered, and Townshend, Val, and Morton arrived safely. But the fourth time there was a sudden ominous slackness in the rope followed by a desperate scream from far down in the depths. There came the thump of a body falling back on the ruin of timber. Cliff gave a frantic order and the winch screamed round its drum as the rope was whirled up. The end was smoking ominously.

“It got him,” Cliff whispered. “We others avoided it, but Gilby must have been swinging from side to side and intercepted the beam . . . Hey, Gilby!” he yelled hoarsely. “Gilby! You there?”

There was no answer from the depths. Val reached out and tied the rope round his waist. “I’ll go see . . .” he announced briefly, and before Cliff could say anything he nodded to Sparks who threw the switches that sent him into the depths.

There was an interval of five minutes in which the party waited anxiously, then came two tugs on the rope. Very slowly, due to extra weight, the winch began to turn. Val emerged with the blood spattered but still living figure of Gilby in his arms.

Gently Val laid him on the floor, turned his head for the emergency kit—but Gilby called him back weakly.

“No use doing that, Val,” he whispered. “I’m—I’m sunk . . . But I guess I can tell you one thing. I—I saw where the electric eye lens is hidden . . . Behind a V-shaped chunk of rock . . . You—you’ll find it. You can avoid it then. I—”

He fell back gently, became still.

The long succession of shocks had left the remaining engineers incapable of further emotions of pity. They could feel the same net of death tightening around them.

“We’ll bury him—over there,” Cliff said quietly. “The others we’ll have to cremate . . . At least we know where the electric eye is and can dodge it even if we can’t destroy it—”

“Death traps!” muttered Val. “What is the reason for all this murdering?”

It was Townshend who answered. “Doesn’t it begin to become evident that all this is a brilliant posthumous scientific trap built by a dying race for a definite reason? Maybe there’s not so much mystery about it at all. All the other planets, as we well know now, are barren. If any living beings came here they’d have to be Earth people—and the chance of beings coming from systems way out among the stars is totally unlikely. Yes, it had to be Earth people—and when they had become clever enough to get here it meant they had an advanced civilization.”

“What are you driving at?” demanded Cliff.

“Just this. No race as advanced as the Martians must have been to build this complex machinery would be petty enough or impractical enough to plan a mere death trap to operate after their demise. They had a specific and vastly important reason. Maybe this is all a test. A trap like this would eliminate an intruder not sufficiently advanced to measure up to the mysterious Martian purpose. Somehow that purpose is connected with that giant ticking ball down below.”

“Sense in that,” Cliff admitted, and added wryly. “If you’re right, it looks as if we don’t measure up to Martian standards. So far we’ve qualified only for the elimination class.”

“Right,” agreed Val. “We’ve got to solve the purpose behind that tick-tocking ball.”

“In the meantime, Sparks, radio to Earth. Tell them to send blast furnaces and to try and unlock the surface valves. We’ll bury Gilby and get to work below with the x-ray machines and flame gun batteries. We’ve little manpower now, and we’ve got to act fast. Let’s get started—”

He halted abruptly as he saw Sparks was trying to interrupt him.

“What’s the matter?”

“That’s the news I was trying to tell you I have,” Sparks said. “We can’t radio. The batteries are dead. Some sort of radiation has burned them all out!”

Once Gilby was buried and a short service recited over his grave, the five returned to the depths, lowering their equipment down the shaft so that it missed the photoelectric eye. They reached below in safety, Sparks leaving his useless radio to help.

“You get to work on the smaller balls with the batteries and furnaces; I’ll x-ray the big one,” Townshend said, and immediately set about the erection of his equipment.

The next two hours were filled with intense activity for all of them, but as far as the flame gun batteries went they had no effect. The balls refused to melt. Even the limited furnaces at their disposal only warmed them.

On the other hand Townshend met with success and pointed to the ciné x-ray screen triumphantly. The rays, passing through the globe, gave a hazy shadowgraph moving picture of what was going on inside. In amazement the others stared on the multitude of black-outlined machinery, intersected cog upon cog, linking up with whole masses of complex mechanism and dominated by a mighty pendulum swinging deliberately to and fro.

“What the devil is it?” demanded Cliff blankly.

Townshend regarded it thoughtfully.

“So far as I can tell it is a cosmic clock—about one of the cleverest ideas I have ever seen. You have seen those clocks on Earth which work by the action of light photons? Well, this is a similar idea but embodying a different principle. This clock is definitely the brain of all these other balls. It works, I imagine, by the action of cosmic rays passing through the planet. Can’t give you every detail right now; I’ll have to get my instruments to work and see what they can analyze of the forces inside the globe.”

“I have the uneasy feeling that it resembles a time bomb,” muttered Val, staring at it. “It started to tick when we broke a circuit. How do we know but what at a given hour the whole thing will explode?”

“We don’t,” Townshend said grimly. “That’s what I want to find out. If x-rays pass through the globe, so will others capable of analysis. You’d better set about helping me.”

Immediately there were further journeys to the surface and one by one detector instruments were carefully lowered, together with adding machines, automatic analyzers, and dozens of smaller attachments necessary to a complete survey. Townshend worked steadily, tireless and grim, checking and computing, apparently heedless of the rather distracting ominous beating of the mighty pendulum.

“I think,” Townshend said finally, glancing up with a strained face, “at the present moment this giant ball is establishing an electromagnetic contact with Earth’s center.”

“What!”

Townshend pored over the instruments and notes again, waved an impatient hand.

“Leave me alone for a while; I want to be sure about this. We’re heading for something mighty tough if you ask me.”

There was nothing the other engineers could do but pace around until they decided to utilize their enforced idleness by cremating the bodies round the elevator base. Once it was done they stood for a while with heads bowed amidst the smoke of the gun discharges, then they returned quietly to the ball room. Townshend greeted them with a shout.

“Boys, we’ve got to stop this damn thing somehow! We’ve eighteen hours to do it in—no more! If we don’t manage it the Earth will be pretty near blown in pieces by volcanic fires, earthquake, and God knows what else. Listen here!”

He went on tensely,

“Between worlds there is a common affinity—a bond of gravitation which centers in the nickel iron core based on each planet, large or small. An electromagnetic beam between worlds is bound to center on the exact center of each world. From here, the core of Mars, an electromagnetic beam is already being generated by the mechanism inside this ball. It has crossed the gap to Earth and automatically centers on the gravitative core of Earth. Earth and Mars are now chained by an invisible but unimaginably strong tunnel, its walls being forced, its apparently empty center being a path down which radiations can pass. Clear so far?”

“Go on,” Cliff invited grimly.

“These instruments prove there is a potential force inside this globe of something like one million billion volts of energy, all of which will be released in one unthinkably terrible battering ram of force when the escape mechanism operates.

“Now, a force of that kind hurled through the electromagnetic beam—tube—and striking the magnetic center of Earth will create terrific havoc. The impact alone will be bad enough, but not half so bad as the abrupt dissemination of energy through all Earth’s metallic seams. The forces of unleashed lightning will be conducted to the surface through numberless veins of metal. Metal will become electrified; in parts seams will explode to allow volcanic forces to shatter forth.

“You can picture the rest. If there are any survivors from electric shock and other catastrophes I’ll be surprised.”

“Just how is this incredible voltage built up?” Val demanded.

“It’s been built up ever since the Martians died or vacated the planet.”

Townshend pointed to various points on the x-ray screen.

“Here is the central mechanism. It is consistently absorbing the electric charges of the planet itself, which it generates by its spin against the ether in dynamolike fashion. It’s been doing it for untold ages. A colossal potential power has been building up all this time.

“Part of it has passed into these other smaller balls by means of deeply sunk underground wires I imagine, which we can’t reach, or to hidden mechanisms such as the one which opened the floor trap. That power has partly expended itself, but the main bulk is conserved for outlet against the Earth. It is so well balanced a unit that it remains fixed at this potential and transmits surplus and overload automatically—so had we not come here for another five centuries it would have made no difference.

“Here,” Townshend concluded grimly, “is the escape mechanism. It releases the potential through the ether shaft. Take a look at it and count the beats of the pendulum!”

The engineers surveyed their watches then glanced at the shadowed machine Townshend had indicated. There was no doubt about it. After every beat of the pendulum a tiny minute hand jerked up a slight degree, bringing it very gradually round to a giant hand fixed in the noon position of an Earth clock.

“See?” Townshend demanded. “Six hours have elapsed since this damned thing started. The numerical order of the clock is pretty similar to our own reckonings. That giant hand points to the twenty-four mark. Now, when the little hand is parallel with it it stands to reason that it will operate this catch on the left here, which you already see is slightly away from its fixture. It widens very gradually until, when the two fingers lie atop each other, the catch will be fully back and. . . .” He stopped, having no need to detail.

“Eighteen hours,” Val whispered, plugging his pipe. “That’s kind of short notice. . . .”

“We’ve got to try something!” Cliff said hoarsely. “We’ve got to get through this ball, even if it’s only an inch at a time. We’ll try blasting too. Morton, you, Sparks, get all the titanite you can lay your hands on and rush it down here. You others help me with the furnaces and batteries. . . .”

Sudden and tremendous activity descended on the cavern. Working at top speed, Cliff, Val and Townshend set up the ray-drillers in v-formation, ten all told, and centered them so that their blinding forces pointed directly on one focal point. They donned dark glasses, slammed the switches, and stood watching.

The brilliance of that one core of flame was blinding even through the dense goggles. At first it looked as though headway was being made, but when ten, twenty, and thirty minutes passed and there was no flow of molten metal hope began to die. Cliff gave a despondent motion at last and cut out the switches.

“No dice,” he muttered, tugging his goggles free. They stood surveying the blackened but otherwise unharmed patch where the rays had played. “It’s not even scratched, and Heaven knows how thick it is. We haven’t enough heat. . . . Titanite might do it.” He stood looking toward the door impatiently but there was no sign of Morton or Sparks, no sounds from beyond the cavern.

“They’re the devil of a time,” Townshend said uneasily.

“Say, do you think. . . .” Val put his pipe solemnly in his mouth.

All three of them swung to the entrance together and stalked through into the adjoining cavern. There was no sign of either Sparks or Morton. There was no response to Cliff’s shouts. He turned quickly to the cradle and pointed to it in surprise. It was loaded with cases of titanite, but of the two men themselves there was no sign.

“Probably they’re getting some more stuff, or else they—” Val shook himself. “What’s the use?” he asked bitterly. “We’ve no time to look into it anyway. Let’s get busy.”

Between them they set about hauling the cases back into the cavern, stacked the long sticks of high powered explosive under the spot they had attacked with ray batteries. It took them an hour to make all the necessary fittings and connections, complete with fuses. The wire to the latter they paid out as they backed from the cavern. They took it with them to the elevator cradle and gradually unwound it from its drum as they rose upward to the higher levels once more.

Once they arrived there they solved the mystery of Sparks and Morton. Both of them lay motionless, face down near the storage camps. They were dead, holes burned in their chests and faces.

“More photoelectrics hidden somewhere,” Townshend muttered. “If we ever get out of this dump alive I’ll be surprised.”

He made a final contact.

“Ready?” he asked, gripping the raised plunger rod.

Cliff caught his arm.

“Wait a minute! I just thought of something. Supposing we blow up the globe? What happens to all that stored potential energy? It won’t travel to Earth—so, just where?”

“Can’t you guess?” Townshend grinned almost ghoulishly.

“You mean,” Val said, lighting his pipe, “that it will radiate to all parts of Mars and that we’re sunk. . . .”

“Just that. Either us—or Earth. We can take our pick—maybe. Considering we had fifty men twelve hours or so ago and there are only three of us left now it doesn’t take imagination to see where we go. Just the same, Cliff, you’re the boss. Do I—?”

“Far as I’m concerned, ram in that plunger,” Cliff replied grimly.

“Shoot!” Val thumbed down his pipe bowl, but his eyes watched the rod with a steady glitter.

Townshend rammed the plunger home. All three of them stood motionless and sweating as a titanic concussion blasted from the depths. The floor rocked under their feet; hot air came gushing up the chasm from the elevator shaft. The walls groaned and rocked under expanding forces and the floor ceased to be.

Cliff felt himself flung into space, went reeling through darkness with the shouts of Townshend and Val ringing in his ears. He landed with a force that knocked all the breath out of his body—but he was unhurt. The lesser gravity had saved him from mortal injury and chance had thrown him on top of the subsidence instead of underneath it. He lay still in an abyss of dark, quivering, listening.

There was only one sound. Tick—tock. Tick—tock.

Then it had failed. The mechanism was still working! Scrambling to his feet Cliff pulled his torch from his belt and tested it gingerly. It flickered for a moment then steadied. He flashed the beam round on an incredible vision of chaos. The explosion had blown the roof out of the cavern, buried several of the smaller balls under a mountain of debris. Equipment, particularly the rubbish magnetizers that had been on the upper levels, had tumbled down here, undamaged thanks to their massively strong casings. Of Townshend and Val there was no sign. They were somewhere amidst all this with the life crushed out of them.

Cliff’s gaze swung to the giant ball. It was smoky black from the explosion, but otherwise untouched and unbudged. The solemn ticking was like a knife to Cliff’s nerves. He looked round him desperately, trying to imagine how much time there was left. Now the x-ray machines had been smashed in the upheaval he had no means of seeing where the indicator had reached.

With a thud he sat down, trying frantically to think of a last possible way. His own life didn’t matter now: it was Earth that counted, with its millions of unsuspecting souls. In the gloom and the dark of those moments the mechanism was his only company.

Tick—tock. Tick—tock. And each move bringing nearer the consumation of a posthumous plot to destroy and avenge.

Tick-tock. Tick-tock. Tick-tock.

As Cliff sat there, each swing of the giant pendulum grew more inexorable, its ticking growing in the utter silence of a dead planet’s interior until it became a thundering vibration that pounded in his ears like the measured tread of Death himself.

Tick-tock! Tick-tock! TICK-TOCK!

Cliff leaped to his feet, his brain reeling.

“No!” he shouted. “By the gods, no!”

Furiously he rushed at the giant ball, beat against it with his fists as though the physical contact would relieve the terrific pressure that was building up inside him; a pressure that bade fair to equal the awful potentiality that was stored up in that sphere of destruction. He backed away with a sob, fingers bleeding, and tore his ray gun from his holster.

He held it on the ball until its charge was exhausted; then he hurled the useless tool at it.

The gun rang against the immutable metal, clattered away into the shadows of the cavern.

Silence fell again, except for the sound of the pendulum, measured, undisturbed, grimly purposeful.

TICK-TOCK! TICK-TOCK!

Cliff stared about, through the gloom.

“Science,” he muttered. “An incredible, diabolic science. These Martians knew too much.”

He moved about among the tumbled rubbish of the explosion, braving the possibility of still further hidden devices of sudden death stabbing burning horror down upon him from the darkness.

“Thousands of years ago they all died,” he went on through clenched teeth, “but they are still here, in spirit, brooding, gloating, like these infernal balls, over the death that is their power to call down. But they won’t succeed in their damned plan! No, by God, they won’t!”

He stared about, a bit wildly.

“Somewhere among all these damned machines must be one that can be turned against that ball; one that’ll open it . . . Funny if their great science didn’t have that power. They hollowed out the balls in the first place, moulded others. Maybe. . . .”

Grimly he searched, prying about in the debris that lay upon the floor, examining each ball that he found, pushing and shoving at each machine he encountered.

But nowhere did he find anything that resembled a tool or weapon or force that would answer his purpose. All of it, it seemed, was for one purpose—to guard the great ball against harm, rather than to destroy it, and to kill all who entered the cavern.

As he stumbled on in growing terror and realization of his utter helplessness to stop the diabolic swing of that giant pendulum, no sudden death lashed out at him.

He shook a fist into the emptiness.

“At least we did that!” he shouted. “We wrecked your infernal control apparatus that operated these murdering rays and traps!”

Tick-tock. Tick-tock. TICK-TOCK.

Cliff’s brain seemed to pulsate in rhythm with the booming noise of the pendulum. It began to permeate his whole body, become the beat of his very heart superseding its natural rhythm, slowing his very life processes to its own deadly pace.

He stumbled on.

Then, suddenly, he came to a rigid halt, his eyes fixed on a looming figure in the gloom. A human form it seemed—a living form.

“Who’s that?” Cliff croaked. “Who’s there . . .?”

Suddenly he rushed forward, incredulous hope flooding into his icy brain.

“Val!” he shouted. “You escaped the landslide . . .”

His voice froze in his throat.

It wasn’t Val. It was a statue; a metal figure, tall as a man, but not like a man. It wasn’t a human figure at all.

He stared with amazement and a growing sense of eerie horror at it.

“My God!” he gasped. “It’s a statue of a Martian!”

He approached gingerly, and looked at it closely.

The figure was that of a spindly-legged, pipestem-armed, and barrel-torsoed creature, with a large head and popping eyes. It stood with one large splay hand over what was evidently a three-dimensional representation of the solar system. Cliff recognized the planets, and even saw a tenth planet where he knew the asteroid belt now to be.^[4]

From the small ball that indicated Mars, a thin band of gray anilum ran to the tenth planet. And from Mars another ran to Earth.

Cliff’s face suffused suddenly with rage.

“So that’s it!” he shouted. “You murdering devils have done this damned trick once before. You’ve already smashed up one planet, and now, even after you’re dead, you plan to smash up another—out of a long-forgotten revenge!”

For a moment Cliff went berserk, and he charged upon the ugly figure of the Martian and hurled it to the metal floor with almost superhuman effort.

The statue fell with a crash, and to Cliff’s utter amazement, it shattered into bits.

“It’s not anilum!” he muttered in an awed voice. “It smashed like . . . like—”

He knelt and examined the shattered figure, and from the debris of it picked up a small whitish piece of bone. As he fingered it wonderingly, it crumbled in his hand, becoming a fine, whitish powder that drifted to the floor.

“Bone!” he exclaimed. “This wasn’t a statue, it was the last Martian himself, perfectly preserved here in his own death-trap! And he was standing there, gloating, even as death came to him, over the vengeance that he had planned for a race that was not yet born!”

Cliff kicked out suddenly with his foot, sending the fragments of the mummy skittering along the floor in all directions. He was sobbing with pure fury after a moment, and then he turned and stumbled away from the horror that he had discovered.

Tick-tock. Tick-tock. TICK-TOCK. TICK-TOCK!

Interminably, on and on, the horrible ticking reverberated through the cavern, and Cliff fled from it, his hands over his ears.

“I can’t stop it!” he moaned. “Not a thing I can do. Here I am, helpless, while that awful voltage prepares to launch itself at the Earth.”

He sat down suddenly on a jagged piece of rock and sobbed like a baby, the reaction of his fear and terror and horror had finally set in. For some moments his frame shook with emotion, then gradually he quieted, and a grim look came to his face.

He sat for some time staring into the darkness, then he rose once more to his feet and strode determinedly back toward the big ball and the invulnerably protected pendulum.

“There must be a way,” he whispered. “No science can be absolutely fool-proof. There’s a way that any slightly clever engineer ought to be able to stop a simple pendulum from swinging. And I’ll find that way! I’ll find it before it’s too late . . .”

But as he stared at the huge ball, he knew that he was indulging in wishful thinking. Perhaps there was a way, but it would take more than the few hours he had left to find it.

Just how much time did he have? He glanced at his watch and cursed. He had smashed it sometime during his wanderings through the cavern. As its hands stood now, he had only seven hours left when the watch was broken. He had somewhere between two and five hours left.

“That’s too indefinite,” he muttered apprehensively. “Even if I do find a way, maybe I won’t have time to finish doing it.”

He began a careful search over every inch of the ball, even piling up debris so he could get on top of it. Once he fell, sliding from the smooth ball, but he was able to rise once more to his feet, although he could scarcely stand on a twisted ankle. After that he crawled about on his hands and knees, inspecting the base of the ball, and trying to find an inlet cable that he could short-circuit.

There was nothing.

Despair seized him once more and he sat thinking.

Tick-tock. Tick-tock. Tick-tock . . .

He began to fancy that he heard whispering in the darkness about him and started and peered around searching for the author of the voice. But he could see no one.

“There’s a way, Cliff,” came a muted voice, seemingly from far away. “There’s a waaayyy.”

Cliff was on his feet, trembling.

“Townshend!” he exclaimed. “Oh my God, I’m going mad!”

His own voice echoed back to him from the distant reaches of the cavern.

“Townshend—going mad . . . Townshend . . . mad . . . going . . . oh my God . . .”

Cliff forgot his injured ankle and began to run, then cried out sharply as it gave beneath him, and he tumbled to the floor once more.

He sat up with an effort, and groaned.

All about him he seemed to hear whisperings, and he trembled violently. He got out his flash, and lit it, sending its bright beam casting about the cavern into every cranny of it, searching for the author of the voices that tortured him.

Tick-tock. Tick-tock. Tick-tock.

For a time, in his growing madness, Cliff had become aware of the ticking of the pendulum, but now it beat back upon his consciousness like the blows of a giant hammer.

He screamed.

“I’ve got to stop it!” he shouted.

And the echoes shouted back,

“Stop it!—Stop it!—STOP IT!”

They become a thundering clamor of many voices, then died away.

Sobered by the tumult, Cliff became quiet, and his eyes cleared. Deliberately he swung the light about the cave.

“Yes,” he muttered to himself. “You’re right . . .”

The beam from the flash caught a ball of anilum high overhead.

“Maybe that was the one that killed Richardson,” said Cliff. A look of rage passed over his face. He sent the beam questing on. Down the walls of the cave, to the floor, littered with debris.

Then on to the giant ball, and beside it to—

The magnetizers!

Then slowly an idea began to form in Cliff’s tortured mind. His idle torch beam was focused quite unintentionally upon the massive bulk of the three magnetizers that had fallen from above in the explosion that had left him the sole survivor.

“X-rays passed through that ball . . .” he muttered. “Other radiations passed through because Townshend measured them on instruments. In that case, suppose I—?”

He jumped to his feet and raced over to the nearest magnetizer. Putting his shoulder against it he shoved and heaved with all his power. It stirred a little, finally righted itself. He stood back, panting, thanking Providence for the lesser attraction that had made his Herculean feat possible.

Without pause, perspiration streaming down his face and limbs, he shoved and heaved and levered the second machine into position, and then did the same with the third.

He was working to the last possible throw of the dice. If other radiations could pass through the globe from inside to outside, then the process could be reversed. Magnetism streaming from the giant horseshoes of the machines, trained on the pendulum inside the ball, should stop its swinging!

If that could be done the machine would be powerless. True, something might happen to the potential energy that would be released, but at least it wouldn’t hit the Earth.

Cliff slammed home the generating switches on the first machine and listened intently. Over the drone of the dynamo the pendulum made a noticeable waver. It was obviously disturbed. There was a definite irregularity.

Cursing himself for a fool for not having thought of the thing before, he closed the switches on the second and third machines. The tripled stream of magnetism had an instant effect.

Cliff lived centuries in those seconds. The pendulum gave a sharp, strident tick, there was a long interval, then a solemn—tock.

Tick—Tock. Tick— Silence.

Dead silence expanding into seconds—minutes! It was a silence of infinity itself here in the bowels of Mars. But the pendulum had ceased to swing. The magnetism had counterweighted it. Cliff wanted to scream, to shout, to tell a planet forty million miles away that it was safe. But he had no way.

Thoughts flashed through his anguished mind. Trapped down here, valves shut, comrades gone, radio smashed—

He became tense. Strange noises were in the giant ball. Curious whirring noises. He stared at it in fascination as it turned a bright, glowing white. It became violet and he felt his skin blister with radiations.

A million pains stabbed through his eyes, slashed and tortured his body so that he dropped in gasping death at the foot of the defeated monster . . .

He never saw nor heard the globe as it exploded with colossal violence to release the energy it had so long stored up.

But they saw it on Earth, and felt it as the Earth reeled from a sudden gravitational change. The report that flashed round the world was ironic and coldly official to say the least of it.

[The end of Mystery of the Martian Pendulum by John Russell Fearn (as Thornton Ayre) & Raymond Palmer (as A. R. Steber)]