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EXPLORERS have often been amazed to find all sorts of life in deep caverns, which evidently have little or no relation to the outer world. It is well-known, for instance, that bats, birds and other forms of life, exist sometimes thousands of feet below the surface of the earth in such subterranean caverns.

How they got there and what their mode of, evolution was, no one seems to know. The present story of Mr. Repp has this scientific fact for a basis, and it certainly makes most interesting reading.

That intelligent beings could only evolve on the surface of a planet, is of course absurd. The chances are that on other heavenly bodies where surface conditions are poor, evolution probably took place from within the planet in most instances, rather than on the outside.

For example, in the case of the Moon, where surface conditions are so poor, it would certainly seem that if the intelligent beings were to be found anywhere, they certainly would be found inside or in the caverns beneath the surface of the Moon.

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THE METAL WORLD

by Ed Earl Repp

IT is hardly possible that anyone in the world is ignorant of the tragedy of fear. From the first day that the invaders popped out of the earth and made their appearance in the heart of every city of consequence on the Pacific Coast, humanity in Western America lived in constant fear. Not since the great earthquake had San Francisco received such a scare and while cities along the eastern seaboard were inclined to consider the invasion as a hoax, the entire Pacific Coast was frantic in its endeavors to find a way to protect its lives and property and retaliate.

There are always those who will not pause long enough to obtain even the slightest knowledge of events as they occur in the world. It is for this class of people that a full * explanation of the Pacific Coast tragedy will have to be expounded again.

To begin with let us dwell on the sudden appearance of the machine in the center of the intersection at Market and Powell streets in San Francisco. Bay City traffic was at its noon height when the thing came suddenly into its midst, its whirling, boring apparatus crashing through a trolley car, spinning it around at a high velocity and finally resting it aside like the flying of a governor from its shaft. Instantly that section of San Francisco was in an uproar and the news soon spread around the entire city that it was being attacked by swarms of giant creatures bent on destroying humanity in its entirety.

Even above the roar and crash of the machine's boring screws that twisted the hard, steel under-structure of the crowded trolley, the screams of the injured could be heard crying horribly for aid. When the giant trolley car was finally hurled into the side of the Emporium Building, the painful, terrified screams came to an abrupt stop and the stupefied pedestrians, who at that hour of the day were strolling peacefully along the walks in the area, were suddenly and completely paralyzed beyond the power of physical movement. They stood, mouths agape, staring at the tragedy before them.

Gradually the threatening machine, protruding from the center of the intersection like a great steel tank, with jagged blocks of asphalt which it lifted in its upward progress leaning against its dull sides, slowed down the whirling, cutting edges on its nose, and stood ominously silent as though its operators were studying its surroundings before exposing themselves.

I am one of those unfortunate mortals who seem to be on the spot when any great trouble, accident or catastrophe occurs and I had just emerged from the doors of the United States Bank at Market and Powell Streets when the machine poked its spinning nose through the asphalt.

I was stunned by the suddenness of the thing when my eyes beheld the trolley car spinning like a top on the whirling blades of the machine my mind went berserk. Like one mad, I dashed down the steps, completely bowling over two statue-like men and a woman standing on the pavement. The collision seemed to restore my mad thoughts. Then I remembered that as a reporter for the Outstander it was my duty to remain and cover the story.

With an effort I halted my mad flight and faced the machine whose boring blades were slowing down. The area in which it had appeared had suddenly become silent except for the ominous whirring of the strange machine's mechanism. It appeared that the unfortunate humans who were viewing the awesome sight of mangled flesh and massed wreckage, notwithstanding the awe-inspiring machine, were hypnotized into immobility. Except for the occasional clicking of teeth of horrified onlookers standing near me, there were no other indications to prove that they were not inanimate objects or clothed statuary.

Market street traffic was at a standstill. Looking up Powell street as far as I could see was a solid mass of heads, strangely immobile, jammed together with eyes concentrated on the catastrophe. Powell street, rising gently from Market toward the hill, offered an unobstructed view of the horrible scene below.

Presently the whirling nose of the machine stopped entirely. From the machine came the sound of weird, mechanical voices, like steel grating upon steel. I stared, terror stricken, at the foreboding tank with its glistening, cutting blades which no doubt had bored its way through the stratas of the earth to its position in the center of the intersection. About midway between the nose of the boring apparatus, and the center of the machine, I noticed a slight movement as a sliding door was silently being drawn open. It was then that I had my first view of the inhuman features of the Demetrians¹.

1: Demeter-an ancient Greek name meaning "Sprang from the Earth" and used by the author to convey that meaning.

To describe the terrifying features that bobbed before the opening in the machine, one must be almost on the verge of insanity. I shuddered as I beheld them, wondering with alarm, what strange world might boast of such a race. I tore my eyes away with an effort to glance at the circle of terrified faces surrounding the silent, powerful machine that seemed to threaten the onlookers with dire disaster. Women in the gay colors of a San Francisco spring day, working men in greasy overalls, and business men nattily dressed, stood shoulder to shoulder, making no move to run or interfere with the machine which had killed and maimed in its course upward.

After my first mad dash down the steps of the Bank, I felt no further desire to get away. And while I had observed the machine and the features of its operators, I should have dashed away to my editorial rooms to pound out the story for the press, but like all the rest, something held me there until escape through the solid mass of humanity would) have been impossible. I am not the type of man to run amuck at the sight of anything so terrifying as the scene in the intersection of Market and Powell. The sight of the dead and dying, mangled and decapitated, was nothing new to me for reportorial experiences offered those scenes—and worse' But no engine of war such as this had ever made its appearance before. Had an enemy of America possessed such an implement of destruction, there would have been a vastly different Atlas of the World than we have today and the United States would have been the subject of some foreign power.

The Demetrians

SAN FRANCISCO was beginning to awaken to the fact that its fair city was being invaded by grotesque strangers from another world. As I stood regarding the features in the opening of the tank, I heard the scream of sirens wafting up Market street from the direction of the waterfront. Louder and louder, like the scream of a tornado, the sirens shrieked as police cars sped on a belated* errand toward the intersection. Someone, I thought, must have had presence of mind to turn in the alarm to the police.

During the few moments that followed, before the arrival of the police, I had a chance to observe the strange creatures. Almost at the first sound of the sirens another sliding door opened along the side of the boring machine and out of it poured creatures that caused pandemonium. The frightened screams of women suddenly awakened to the fact that their lives were in danger, and the hoarse shouting of men broke the spell of immobility that seemed to have gripped the onlookers as the Demetrians made their appearance in the street. I glanced around the half mile deep circle of pedestrians surrounding the invading machine. Women fainted and were trampled. Men, made beasts by terror, plunged madly into the jam in an insane effort to escape the grotesque creatures.

As those in the rear of the first few lines forming the circle became aware of the cause for the sudden milling in front of them, they too stampeded and the entire mob was running amuck. I held my ground just in front of the circle and steeled myself to the shrill screaming of the women. I could not have helped them and my better reasoning told me that I was safer away from the milling, insane humans. The Demetrians had made no hostile move as yet, I considered, and while their appearance was sufficient to cause the human mind to run berserk, I nevertheless remained near them rather than chance almost certain death under the feet of the panic-stricken multitudes.

The scream of the police car sirens was drowned by the shouting of the terrorized mob. I turned for a full view of the Demetrians as they arranged themselves in a circle around the machine. As I swung around I felt my elbow touch another and I found myself looking into the serious face of acquaintance, Professor Roger Blackton, whom I had interviewed some weeks before concerning the possibility of X-raying the earth. His eyes were settled intently upon the strange creatures pouring out of a series of openings along the sides of the tank, taking up position like a squad of special police guarding a shipment of gold. I placed a hand on his shoulder and he leaped aside like one suddenly pricked with a sharp instrument.

"I didn't mean to frighten you, Professor," I apologized at the top of my voice so that he could hear me above the roar of the mob.

"Oh, hello, Dowell!" he managed to smile, "I guess sight of those things shattered my nerves. I wasn't thinking of anything but the terrifying faces of that scourge—for scourge of the earth they are! My God, Dowell, what destruction they have caused among the people!"

"It is frightful, Professor," I conceded, shaking my head. "What the devil delays the police?"

"It's probably difficult for them to negotiate that mad mob, Dowell, without killing right and left."

I shot another quick glance at the creatures surrounding their machine. The circle was widening slowly as the Demetrians crawled like giant centipedes toward the milling masses of humanity struggling vainly to escape. Yes, like giant centipedes they came on in an ever widening circle!

I shuddered as I regarded them and with my hand by Professor Blackton's arm I felt a tremor surge through him.

The Demetrians, maintaining some sort of communication between each other by that rasp-like metallic voice, were not at all unlike the centipedes more commonly known to childhood as the "thousand legger." There was distinct similarity between the two and yet somehow, the features on their large, bony heads seemed somewhat human! From their heads down to the tips of their short pointed tails, they were decidedly Myriapoda. They were more than six feet in length, their bodies supported by tube-like, flexible legs that numbered in hundreds, running under their bellies in two rows. Each wore a metallic belt containing small shining cylinders.

Over the heads of each waved six strong, powerful arms that seemed to be jointed at almost the same sections as the human arm. At their ends were four-fingered hands, thumbs absent! In the features of each a pair of deep, fathomless eyes glowed luminously like pale uncut rubies. Their mouths, were like the beaks of amphibious animals of the Rana genus. Occasionally they opened their beak-like lips and snapped them like a frog snapping at a fly. Long red tongues flicked forth and disappeared again in deep, cavernous mouths.

Professor Blackton nudged me and yelled in my ear to observe pistol-like objects held in their hands. They clutched them tightly as though afraid to permit them out of their hands.

"Weapons, Professor?" I shouted loudly.

"Certainly, Dowell!" he yelled back. "Do you recall that a few weeks ago I stated that I believed the interior of this old world of ours contained some sort of creature that might be capable of annihilating the human race? Well, Dowell, what I said has come true. These creatures are from the Inner World and the existence of humanity is from now on doubtful! Yes, my friend, they are the ray guns of the Inner Beings!"

"Oh come, Professor!" I yelled into his ear, "They've got into your blood! You cannot mean that!"

Professor Blackton chewed nervously at his lips. He stared at me and spat out a dribble of blood.

"For years I've endeavored to tell the world that the inner earth was just as habitable as the outer surface but none would believe. Now here it is to prove my contention! Here's ample proof—these Demetrian beasts."

"What would they want to do on the surface, then?" I shouted.

Suddenly I saw a greater commotion down Market street. The police cars must have opened a path through the panic-stricken pedestrians.

"How do I know, Dowell!" the Professor yelled. "Probably they want something we have or—Look out, Dowell! Here they come!"

There was a sudden rush of wind as heavy bodies hurtled past me. I was bowled over and over. Sharp thorny objects pricked my skin as the Demetrians raced over me. I caught a glimpse of the Professor. A Demetrian was dashing over him and he shielded his face with uplifted arms to protect it from the pincer-like legs of the creatures.

CHAPTER II
The Massacre

WITH incredible speed—speed as only hundreds of legs can create, the centipede-like creatures raced toward the struggling mob. I glanced at the machine. Demetrians were arranged around it as a protective measure, their oddly-shaped hands held high over their heads, ray guns aimed in a deadly circle. As I lay I wondered what had been the reason for the sudden rush. Why hadn't they destroyed Professor Blackton and myself where we stood instead of merely racing over us? I looked at the Professor. He was rising to a sitting posture, his eyes glued on the Demetrians as they reached the edge of the panic-stricken multitude.

Suddenly there reached my ears a bedlam of blood-curdling shrieks. I leaped to my feet for a better view of the scene. There before my very eyes the Demetrians reached the edge of the jammed pedestrians! At that instant I heard the sizzle of their terrible rays as they swept into the mob, cutting clean paths through it. I saw a ray strike the Bank Building and a wide opening appeared in its walls. Then there came a series of roaring crashes as other buildings, their structural frames weakened by the devastating rays, crashed down. Dust and debris filled the air. My nostrils twitched under the odor of scorched flesh!

Professor Blackton cursed loudly and sank back flat on the asphalt surface, burying his face in his arms. The Demetrians had suddenly turned and were racing back to their machine. I dropped to the street and covered my face. Almost instantly I felt the prick of hundreds of sharp feet as they raced over me. My skin seemed numb from the effect and I lay for what seemed hours before my senses were suddenly aroused by the staccato throb of machine-gun fire. I looked up, half dazed.

What I saw caused my* thumping heart to leap. Lined in crescent formation on the edge of the insane mob, and lying flat on their stomachs behind a row of fire-spitting machine guns, were San Francisco's crack police gunners 1 Each single gun was vomiting pellets of lead and steel into the circle of Demetrians who seemed too stunned at the suddenness of the attack to bring into play the terrible powers that existed in their ray pistols. I heard the rapid tattoo of machine-gun bullets striking the metal surface of the cylinder. They seemed to glance off the heavy steel surface of the machine for I heard the whine of ricochetting slugs passing over my head like so many bees.

Strangely the Demetrians seemed not at all effected by the rain of bullets. Their beak-like lips seemed to open in sneers of contempt. None of them showed any outward effects of the slugs yet I felt that the aim of the police was anything but untrue. Perhaps the creatures were immune to injury or death. What manner of being were they, that they could stand the ceaseless fire from a dozen man-made implements of destruction?

Then, as though by some pre-arranged signal, the Demetrians brought into play again their terrible pale red rays! Instantly the intersection of Market and Powell was bathed with the sizzling beams from their pistols! In one single barrage of rays three of the prone police machine gunners vanished in a puff of acrid smoke and the guns in front of them crumpled as though made of wax instead of highly tempered steel. For an instant the throb of the other guns ceased. Then with renewed vigor they opened fire again valiantly. But to no avail. The Demetrians did not falter for an instant but opened their beaks sneeringly.

As I lay on the asphalt, fearful to rise lest a misdirected ray strike me, I watched the scene with insanity creeping into my brain. I cast a glance at Professor Blackton. He too was lying prone on his stomach, regarding the raging battle of uneven odds. With horror striking deep within me, I saw a pale red ray striking the struggling mob of humans behind the valiant policemen. The beam cut a clean path through it! I caught a glimpse of the tower clock on the ferry buildings at the foot of Market street through the pink smoke that floated over the swathe. Already the atmosphere was stale with the taint of scorched flesh and I wondered how long it would be until the Demetrians actually swept the city clean of human life!

Suddenly I was aware of a burning heat to my left. I looked up. A thin shaft of pale red light was passing over me, to strike the corner of a towering building on the southwest side of Powell. Instantly the corner vanished leaving a gaping hole where the ray had penetrated skyward.

From an opening aperture high up along the side of the United States Bank Building, I heard a sudden staccato rattle of a machine gun; then a barrage of Demetrian rays sought it out and the side of the building crumpled like paper, showering the street below with debris.

Presently I heard the throb of air screws high overhead. Professor Blackton yelled at me to hug the asphalt. There was the roar of an explosion. I was showered by fragments of rock and particles of vermilion-colored matter. But one infinitesimal bomb was all the naval flyers had time to drop before a Demetrian ray instantly annihilated the two planes. They vanished in a puff.

From somewhere inside the boring machine there issued a deep-throated clanging sound. Then as though tiring of the game they were playing the Demetrian warriors began to enter it in groups of threes. The remaining police gunners still bent on wreaking as much damage as they could continued firing. I saw a group of four Demetrians detach themselves from the circle and race toward the remaining guns. As they neared the officers they brought into play their deadly rays. The prone figures vanished and with them went a hundred struggling, jam-locked pedestrians. As the creatures finally crawled into the machine and the opening slid to a close the drone of high powered mechanism could be head from the strange cylinder.

The Demetrian's Threat

AT a small observation window that was still ajar, appeared a grotesque face. Like a whipped cur I watched the Demetrian's beak-like mouth open and I heard a biting voice that cut into all other sounds like a steel file running across a rough surface. My teeth went on edge at the sound.

"Hear ye, Surface World, the message sent to you by Progrious, exalted ruler of the Inner World of the Earth!" the voice rasped in an almost unintelligible jargon. "You of the Surface are commanded to abandon all further exploitation of the earth's resources! They are ours! We demand unconditional surrender of them. If you disobey his command the Inner World will sweep your Surface World clean of its scum! You have taken more than your share of this earth's resources—its gold—its ores—its oils and its gases. What remains belongs to Progrious and he shall retain it even at the cost of the earth itself! Hear ye, Surface World—and take heed!

"You may wonder what happened to your ship the Cyclops which vanished thirty years ago during your world war. I will tell you so that you may know our power. On the ragged coast of your land called South America where the ship stopped in a storm, we captured many of your crew and with our ray machines utterly destroyed your ship. The men we captured we tortured until they taught us your language and told us about the world of the surface. How you obtained the manganese ore they were carrying—a metal that belonged to us. We killed those men when we had learned what we wished. We know that you mean to exploit our riches, but again we warn you, they are ours!"

With the last ominous, threatening words, the opening was slammed shut and the machine's mechanism whined. The tank instantly disappeared into the earth, sending high into the air a towering shaft of pulverized rock that showered the entire city of San Francisco with lung tickling dust! Following the almost instantaneous departure of the machine, it did not take long for the streets of San Francisco to clear. The havoc wrought by the invasion was a havoc that struck terror deep into the heart of the citizens. The number of lives that were lost as the result of the Demetrian invasion was indeed great. But no greater than that suffered in other cities along the Pacific Coast as I learned when I tramped wearily into the offices of the Outstander.

The editorial rooms were in a state of unleashed activity! The radio, telephone and cables sputtered under the pressure of constant usage. The wires hummed with reports from Los Angeles, San Diego, Seattle, Portland and points as far east as Salt Lake and Denver. Each of the cities had been visited by the Demetrians and to each had been given the warning to abandon all further work in removing the world's natural resources from the earth. Los Angeles reported that at precisely high noon, a Demetrian machine plunged upward through the car rails in the center of Seventh and Broadway and suddenly let loose a barrage of deadly rays. Three heroic officers had lost their lives in the City of the Angels when they drew their guns and attempted to shoot it out with the invaders. Santa Fe Springs and Signal Hill, Southern California's greatest oil fields were visited by a machine and destroyed, their reserve tanks left burning, derricks and towers laid in ruin.

From other cities came similar accounts. The havoc wrought in Seattle resulted in the destruction of many buildings and the loss of considerable life. When the Demetrian machine popped up there, a celebration of some sort was in parade and the whirling blades of the invader tore into the mass with frightful casualties. Seattle reported that everyone in the city was leaving at once for higher ground in the mountains thinking to escape further encounters with the invaders.

In Salt Lake City, a machine appeared on the grounds of the Mormon Temple, tearing out several sections of the building as it arose. The State Militia attempted to destroy the machine but gave up the struggle after half of their number had been wiped out by rays. Denver was hard hit, reports declared, and San Diego suffered a terrible loss. Rockwell Field there had been practically destroyed. Portland told in cryptic code of the invasion and stated in no uncertain terms that it had no intention of giving in to the demands of the Invaders. While they did not show any hostility toward the Demetrians, they told them that mining in that section would continue regardless. To retaliate the creatures felled ten city blocks!

Dejectedly I sought out my desk and sat down hopelessly. I had not been the only reporter from the Outstander who had witnessed the scenes at the intersection of Market and Powell. Others had watched the destruction from the roof of the press building and flashed the news around the world long before I succeeded in finding my way through the frenzied mob.

Not least of the sensations created by the beasts was the information they gave us about the Cyclops. For twenty years the disappearance of this 19,000 ton collier of the United States Navy had puzzled the world. Leaving the Barbados, West Indies, on March 4, 1918, with a crew of 15 officers and 221 men, and 6 officers and 51 enlisted men as passengers and carrying a load of manganese ore, it had never been heard of since. That the Demetrians could have completely destroyed the ship we could not doubt, having seen the evidence of their strange powers in the raids on the cities. That they should exact information about our world from the unfortunate captives and then kill the men, betrayed natures at Once cruel and relentless. The world was faced with a powerful enemy.

For long minutes I sat, head lowered, eyes closed to shut out terrible, persistent visions. I turned at the touch of the City Editor's hand as he reached out and tapped me on the shoulder.

"Snap out of it, Dowell," he said, chewing savagely at a cigar. "Chase up and interview Professor Blackton! He called for you this minute. He may have something important to say And, by the way, dig up that old statement of his concerning life within the globe."

CHAPTER III
The Professor's Hope

"WE meet again, Dowell," Professor Blackton said pleasantly, opening the door of his laboratory in response to my ring. "You don't look much the worse for wear."

"No," I said, "but I feel as though I've been stung by a whole hive of bees. Those devils have mighty sharp toenails to pierce a man's coat, vest, shirt and so on."

"Well I'm glad it wasn't a Demetrian ray that pierced you!" he grinned. "You came pretty close to getting that ray that struck the Flobart building. I thought they had your number for a second. But come right into the laboratory. I want to show you something."

"With pleasure, Professor," I replied, wondering what was in store for me. "I hope you've conceived some method of retaliation against those contemptible insects! They deserve complete annihilation!"

"That's just what I've been working on, Dowell! When I said years ago that it was possible for life to exist below the surface of the earth, I meant just that and began work to learn just what sort of life it was. At last I have reached my objective——I'm going to open up this old world and see what its made of!"

"You're going to what?" I queried, astounded.

"I'm going to X-ray the globe, Dowell!" he said, enthusiastically. "You see, I have developed a series of tubes embodying the combined radiations of the Rontgen Rays with the Coolidge tubes. It was not until a short hour ago, however, that I've been able to add to the results the powerful radiations of a special tube made for me by Bliss—the Bliss Vacuum. I have worked out the phenomena of interference and ascertained that electrostatic forces have been the cause of the past failures in X-raying great, solidified bodies like bank vaults, buildings and—the earth. I have overcome these interfering obstacles by the process of combining infra-red rays with high frequency cathodes with results that the objects will be penetrated by ultra-red rays making the bodies almost as transparent as glass. On passing from air into water, carbon disulphide, aluminum, rock, basalt, iron, lead or any other substantial material of the earth, my ultra-red rays will suffer no noticeable diffraction.

"As to the intensity of the rays, I have no fear. Their power to penetrate, through the combined radiations of the tubes and systematically controlled vibrations of light, is unlimited. I will have complete control over them by a system known as the X-ray galvanometer."

"That's wonderful, Professor!" I said warmly. "Just think what your X-ray will do then, for locating such valuable resources as we have in our earth. It will be the greatest divining rod the world has ever known! Why, Professor, an X-ray of the earth will reveal the exact locations of gold, silver, platinum, oil and——"

"Correct, Dowell, my boy. But you seem to forget that we of the Surface World are commanded by the exalted Progrious of the Inner World to cease removing the resources from the globe," Professor Blackton said seriously. "The resources are remote from our minds now. Our lives must have first consideration if we must continue to exist."

I felt my brows go up automatically and scowled.

"Of course the Surface World does not intend to knuckle without a fight, Professor," I said.

"That's true, but you cannot fight the unknown, Dowell," he said, knitting his brows. "If my X-ray is the success that I feel certain it is, then the Demetrians will no longer think they can frighten us into complying with their demands. I shall learn their secrets by X-raying them, and by their own methods we shall wipe them out entirely. By that alone we will have peace and no further fear of them. My only hope is that the government will co-operate with me to the fullest extent."

My heart leaped. If Professor Blackton was of a sane, reliable mind; then what more could we of the Surface World ask of him!

The Inner World

"MY God, Professor, there's millions of them— literally millions—crawling around like vermin of the dead! Here look into this funny shaped dwelling!"

Professor Blackton climbed down off a high structure which supported a long, heavy tube of shining brass, and strode swiftly to my side where I stood gazing tensely onto a screen on which was reproduced the life miles upon miles below us. There exposed on the screen of the Professor's own creation, lay the domain of the Demetrians!

The entire Inner World lay open in miniature on the screen and the Demetrians, millions of them, were crawling through mazes of strange vistas and tunnels that formed the thoroughfares of a world hewn from solid metal! A metal world! Far below the surface of the earth, could be seen hundreds of their machines, cutting blades spinning at front and rear, burrowing through the earth's stratas of metal and rock like gophers in soft, dry earth. The pull and push of their blades carried them swiftly as though they were burrowing through sand. Their progress could be clearly followed by loose, pulverized earth that was left in the tunnels behind them.

The Inner World seemed to have been hewn from a solid mass of metal far in toward the core of the earth! The material glistened like the polished surface of a meteorite! Here and there in the metal walls that formed the sides of what appeared to be Demetrian dwellings, were occasional dark spots of iron, while the prevailing brilliancy of the majority of the metals glistened under a pale red luminosity like polished nickel. Directly in the center of this strange domain stood a great mausoleum-like structure surrounded by doubtless thousands of the strange boring machines. The architecture seemed oddly familiar, being similar to that of the far east. I turned the screen over to Professor Blackton and stood aside, regarding the X-ray apparatus while he studied the Demetrian objects officially.

Professor Blackton's X-ray machine seemed hardly different from the giant telescopes of Mount Wilson observatory. Although somewhat narrower and not quite so long as the great Hooker telescope, the X-ray would have been accepted at once by a layman as being an instrument of astronomical science. But if one had observed the mechanism of the apparatus in the interior of the tube, and in substantial aluminum housing arranged at its base, then perhaps it would have been accepted for just what it was—a great X-ray machine! Arranged in positions at the brass cylinder's base were various tubes aglow with many beautiful colors. By some process which I did not understand, Professor Blackton had prepared prism reflectors surrounding the glowing tubes that carried their radiations into the cylinder which in turn grounded them into the earth in the form of penetrating beams.

By a strange network of copper induction tubes it appeared that the rays were radiated from the earth and concentrated into a shining silver ball which forced the transparency of the X-ray pictures into a heavy leaden box under the screen. By another process known only to Professor Blackton, the X-ray pictures were reproduced on the screen with results that thousands of cubic miles of the earth's interior were defined clearly before us in a space not more than thirty-six inches square. But, above all, the domain of the Demetrians lay exposed with stereoscopic clearness and Professor Blackton was making the best of the situation.

He twisted a tiny knob. A unit of delicate mechanism began to hum somewhere under the screen. I caught a glimpse of dark paper sliding over rolls under the luminous square, to vanish in a circular tank containing some rank acids. Professor Blackton had even prepared the delicate, intrinsic process for reproducing in photographic form the objects defined on the X-ray screen!

"Dowell!" Professor Blackton called suddenly, as I studied a series of large, glowing tubes.

"Yes, sir!"

"Stand over to the left, just beyond that drying tank, and catch the photographs as they come through! I haven't erected an accepting chamber yet. You will want to take those pictures to the Outstander. Handle them carefully, as they are invaluable."

"Lord!" I gasped, laying my hands on the first strip of paper, now white and dry with reproductions of the Demetrian scenes printed on it. "What a story! What a life saver for humanity! And vengeance——ah, that was it, vengeance on the scourge of the earth! Vengeance for those poor people of the Cyclops. We'll fool the Demetrians! They don't seem to give us credit for intelligence! They believe they are safe from the wrath of the Surface World. We'll show 'em!"

"Yes, my friend, we'll show them something!" the Professor stated flatly.

As the dried photographs came through the drying tank I found myself visioning a wholesale invasion into the metal world. Then suddenly I remembered that miles upon miles of solid rock and metals barred Surface bound humanity from invading the Metal World below, and my hopes fell disconsolately.

Presently Professor Blackton stood erect and pressed a button at the control board. The screen went dark as the last strip of photographs came into my hands. I placed it on a table with the rest and regarded the Professor. He stared at me for several seconds and then motioned for me to sit down at a desk located at the other end of the laboratory. Handing me a sheaf of paper he bade me jot down his statements. Ready, I watched his face. It glowed with deep satisfaction and I wondered how he could express such emotion in the face of a situation that spelled almost doom for the human race. For certainly it could not exist without the resources that environment had made necessary to maintain its existence and we would fight to the last for those things.

"My friend," Professor Blackton began, "my experiments have been a success! I have succeeded in creating a system for X-raying the earth! You have seen for yourself. There should be no doubt in your mind!"

"But Professor," I interjected seriously, "How will your X-ray aid us in retaliating against the Demetrians?"

He laughed pleasantly.

"I was coming to that, Dowell," he said affably, seating himself on an upturned container beside me. "Are you ready to proceed?"

"Shoot!" I said, simply.

CHAPTER IV
Desperate Straits

WHAT Professor Blackton told me there in the semi-darkened laboratory in his home perched high up on Nob Hill caused my heart to skip many a beat. After he had finished making lengthy statements in cut and dried scientific parlance, I could see that the Surface World need have no further fear of the Demetrians. In my story which covered the entire front page of an extra edition of the Outstander, as everyone knows, I gave a detailed account of his statements, plans and hopes. I told how such strange creatures as the Demetrians came to exist in the world far below us.

Without flourish or padding, the accounts acquainted the public with Professor Blackton's proposed plan for retaliation against the Demetrians. San Francisco abandoned its fright to some extent and went wild with enthusiasm.

Professor Blackton's statements were broadcast around the entire world and the wires hummed in return with expressions of appreciation and confidence from the cities that had been invaded. The Governor at once wired a lengthy telegram to the publisher of the Outstander offering publicly all the wealth and materials that the State of California possessed, to the disposal of Professor Blackton, who in turn called the Governor on the phone and made known his needs. His every wish was granted and events were not long in shaping themselves after the State of California opened its vaults of wealth and resources to the cause. Official wires from the Federal Government gave California a staunch backing. The states and city governments in whose territory the Demetrians had appeared likewise made known their desire to aid the Professor in his plans for retaliation against the inhuman creatures of the Metal World.

Professor Blackton appeared to have drawn into a shell after making his statements to me in the laboratory. He seemed unapproachable for several hours, and then out of a clear sky he phoned me at the office.

"Dowell," he said, "I'd like to have you accompany me to Alameda. Can you make it?"

"Meet you at your home in twenty minutes, Professor," I replied, grabbing my hat. Waving at the City Editor, I dashed out of the editorial rooms and into the queerly vacant avenues. Market street was deserted. In the growing dusk of evening the absence of the throngs gave the city the appearance of being abandoned. Except for patrolling officers and a few hurrying pedestrians here and there, gay San Francisco was otherwise a dead and forsaken City!

When I reached Professor Blackton's residence he was standing at the door, hat in hand, staring at the sky in the direction of Alameda. His face seemed to have aged during the last few hours and his shoulders, usually straight and military, drooped.

"What's wrong Professor?" I asked, mounting the heavy stone steps that led to an elevated patio in front of the house. "Are you ill?"

"Sick at heart, Dowell!" he said, shaking his head. "Look!"

He lifted a shaking hand and pointed at the sky.

"My Lord, Alameda is afire!" I almost shouted.

"Yes, Alameda——the government yards, have been laid to ruin by the Demetrians! They've learned somehow of my intention to construct my Earth Boring machines, Dowell, and laid waste the materials stored in the government warehouses."

"How——how in h——?"

"Yes, my friend, how did they know? Some system of keeping tab on our activities, I suppose. It looks bad for us, Dowell."

"What do you mean, Professor?"

"It means that if they continue to interfere with my plans then we will be at their mercy entirely. But come, I've wired Mare Island. They'll drydock several cruisers and strip off the armor plate to build our machines. We can't lose a minute. Now that they believe they have us on the run, the beasts are likely to appear at any time in force!"

The Golden Gate airport was deserted except for one small pursuit ship bearing the insignia of the United States Air Forces. Where ordinarily planes should have been seen by the hundreds, a single craft rested at the end of the field like an abandoned chick. As we raced across the field, the ship made contact and her airscrews roared, causing her to tug at the blocks. The pilot motioned me into the gunner's cockpit. I climbed in while Professor Blackton seated himself without helmet or goggles, in the fuselage. Before I had become settled, the ship was racing down the field. With a sudden take-off and steep bank into the air, the ship heeled Southward. I clutched at the sides of the fuselage to retain my seat, as the craft straightened out with a jerk. The pilot seemed to understand that speed was required in Professor Blackton's mission. He open the throttle to capacity and the ship scudded through the darkening heavens like a migratory bird.

Building the Borers

WHAT transpired at the Mare Island Navy Yard is a matter of history. In brief, I might re-count that six battle cruisers were stripped of their great armor plating, and the plates lifted in huge slabs into great, open hearth furnaces. Sweating men worked tirelessly at the furnaces. Molten steel, sputtering and singing loudly under the pressure of the blasts, began to pour out into giant ladles. Overhead cranes lifted the ladles of sizzling metal and carried them to another section of the mile-long shops. There the contents were dumped into other furnaces to be alloyed with a prepared combination of metals that with the armor plating added, were to form the surface hulks of Professor Blackton's Earth Borers.

Fascinated, day after day, I watched the activity and the various processes from a control cabin slung under the cross beams of a giant crane. This was my vantage point when not sleeping or eating. Occasionally I caught a glimpse of Professor Blackton. Frequently I saw him test the glowing metal as it poured out of the alloying crucibles with great cylindrical moulds. He seemed alive with energy and appeared to be watching every single process in the making of his machines. When he was not to be located in the furnace section he was to be found in the machine shops, where high velocity turret lathes were turning out boring blades and mechanical parts for his machines.

With growing uneasiness as the days passed I found myself speculating upon the Demetrians. One day as I watched several giant cylinders being lifted out of the moulds and carried into the machine shops for assembling, I wondered why the scourge had not appeared at Mare Island and laid it in ruin to prevent the construction of the Professor's boring machines. Perhaps after all, I thought, the Demetrians were not aware that Mare Island was the point of that activity. Or perhaps they feared to show themselves in view of a dozen battle cruisers swinging at graceful anchor just off the coast with batteries trained on the area surrounding the shops, ready to launch their missiles of destruction at them on an instant's notice. But nevertheless I could not allay my fears that their pale red rays would eventually find a perfect mark in the long buildings despite the presence of the cruisers.

Then one day from sheer exhaustion I dozed in the crane's cabin. The hubbub below continued, yet I did not hear it. Frequently I awoke with a start when the crane quivered under the weight of its burdens. Presently I became aware of a different sort of sound than those to which my hearing had become accustomed. I stared through the cabin windows to the floor below.

Elevated upright on platforms in the center of the floor were a dozen huge, formidable-looking cylinders. So similar were they to the Demetrian boring machines that I felt suddenly afraid that the navy yard had been invaded. But my fears were short lived when I caught a glimpse of Professor Blackton surrounded by a knot of men, standing near the tanks. Elevated as they were, the boring blades of the machines whirled clear, emitting high sounding shrieks as the wind of their own making whistled sharply into the grooves in front of the cutting edges. The machines contained two boring noses, one on each end, and like the Demetrian tanks, had a number of sharp guiding fins protruding from their rounded sides. In all, they looked to be exact duplicates of the machines that had invaded the cities of the Surface along the Pacific Coast. I felt a sudden warmth of feeling for Professor Blackton. He had learned at least one of the Demetrian secrets!

With a feeling of pride in the Professor I climbed down from the cabin. Through the open windows of the shop I could see the heavens lightening in the east. When I reached the floor the cool breezes of early morning, drafted through the open panes, brushed my face. The roaring furnaces had long since been shut down. The work of assembling the machines had required the attention of every available man in the yards. I felt guilty of desertion for having remained in the crane cabin, but I had gone there out of danger at Professor Blackton's request. I could not have aided much in any event.

The Professor nodded as I approached the group. The wind created by the long line of whirling blades lifted my hat and sent it soaring. I let it go in my eagerness to inspect the cylinders.

"Looks like you've done it, Professor!" I shouted to him. "They're Demetrian tanks or I've never seen one!"

He appeared not to have heard and turned to speak to an officer in the group.

"Follow these instructions out to the minute, Commander," the Professor yelled into the officer's ear, handing them a sheaf of parchments. "I'm going back to my laboratory to watch the results in the X-ray. In exactly one hour you will send the machines into the earth from where they rest. I'll advise you of the results personally. And thank you for your wonderful co-operation."

"My only hope is that you will succeed, sir," the Commander replied, reaching out a grimy hand. "I shall make no error, you may rely upon that!" Goodbye, sir!"

"I have utmost faith in you, Commander," the Professor said. He turned to me. "We shall return to the laboratory, Dowell. I'll explain everything when we——"

Before he could finish his sentence the entire world seemed to sway under the vibrations of sudden explosions. At Professor Blackton's heels I raced to the windows and stared out over the Pacific. A great cloud of black smoke was rising from the water and I caught a glimpse of a conning tower as it vanished below the surface.

"God!" Professor Blackton groaned, "they have come—they've destroyed a cruiser! Down flat, Dowell—lie flat!"

Quickly I dropped to the floor. Another tremendous explosion shook the earth, then another and another. Without waiting to see the cause of the explosions or the results, Professor Blackton leaped to his feet and raced frantically toward the row of Earth Borers, their blades spinning at unbelievable velocity. I heard him yell loudly to the Commander.

"Let them down—let them down!" he called at the top of his voice. "Let them down! Quick!"

Instantly the machines were lowered. The boring blades bit with a whine, into the concrete floor of the shop. Professor Blackton raced away from them under a shower of pulverized cement. Under their great powerful forces the machines were quickly disappearing into the earth. The entire roof of the building was lifted high into the air under the force of the upward discharge of earth cast up by the borers. I hugged the floor near a wall expecting momentarily to be crushed to death by the fall of the heavy steel roofing.

Presently there came a frightful crash as the twisted mass fell to the ground yards away. I stole a glance overhead. My eyes beheld a criss-cross of pale red rays as they struck the walls of the building toward the top. The walls vanished as though they had never existed, clipped as clean as if sheared off. For a long time I lay still figuring that the next second would be my last. But I failed to feel the heat of Demetrian rays. Heartened, I looked around. Professor Blackton was lying prone on the floor near a dead furnace, regarding me through wide-open eyes.

We lay still for several more moments and then he waved to me. I arose and followed him quickly out of the building. Others trailed us. Outside I glanced around, glad indeed, to have escaped thus far the devastating rays of the Demetrians. In a field to the left lay a huge, twisted mass that was once the roof of the Navy Yard shops. I caught sight of feeble motion underneath it and then there came into full view suddenly the grotesque form of a Demetrian.

"Professor! Look——the Demetrians!" I cried, pointing.

Overhead I heard the hum of air screws. I looked up and saw six closely assembled objects racing earthward. Almost instantly there came the roar of a terrific explosion. The bombs had struck the mass of twisted steel. Nothing could survive that demolishing barrage, not even an invincible Demetrian tank.

CHAPTER V
Something About the Demetrians

IN the laboratory of Professor Blackton we watched the rapid progress downward of the earth borers—emissaries of destruction that were hoped to destroy the Demetrians in their own Inner World.

Quickly after our arrival at his San Francisco residence and laboratory, Professor Blackton set to work re-arranging his X-ray screen. In a few short minutes he had finished his work and the scenes disclosed by the X-ray were projected onto a larger screen arranged on the wall of the laboratory.

In response to a number of telegrams sent by the Professor many famous scientific personages were conversing in the Blackton living room when we returned. Professor Blackton was at once besieged by his fellow scientists and congratulated from all sides for his remarkable achievements with the X-ray. He immediately waved them into the laboratory with a few words of greeting, and they arranged themselves in chairs in front of the larger screen to await developments.

When the first of the penetrating beams entered the earth and radiated their fluorescence on the screens, the laboratory became a hubbub. To me it appeared that each spectator in the room was trying to talk at once, with results that the room reverberated with a meaningless jargon of unamalgamated sounds. Gradually, as the X-ray beams penetrated deeper, disclosing on the screens the various stratifications of the earth's inner materials, the scientists became quiet, and stared intently at the scenes in front of them.

Presently Professor Blackton twisted a knob on the control board and the screens glowed brighter. With stereoscopic vividness the domain of the Demetrians lay exposed before them. They gasped in astonishment.

"Gentlemen," the Professor said, "you may observe the twelve earth borers which we sent into the ground at Mare Island this morning. Within fifty minutes they will reach the Inner World which you see in the very center of the screen. What do you think of the Kingdom of Progrious? Quite a world, is it not?"

"A metal world!" I heard one of the scientists gasp.

"A metal world, doctor," Professor Blackton agreed, "but an evil one! In an hour I hope it will be no more."

"But how do you propose to wipe it out, Professor?" asked an eager voice. "Can you enlighten us as to the origin of these creatures?"

"I think I can explain within a short time, my friends," he replied, softly.

"When I first beheld this strange world yesterday, through the X-ray screen in front of me, I became firmly convinced that the Demetrians were products of a strange environment. At some distant period they may have been surface beings who became enveloped underground by the upheavals of the Volcanic Era. Unable to escape, they were forced to adapt themselves to that environment. Results were that they developed to the form of an insect, the only form of life capable of existing below the earth's surface. Like we of the Surface, they gradually developed material things such as artificial lighting, transportation, dwellings and other objects you see on the screen before you, as well as long lines of science of which we have been in ignorance. Their rays, for example. Having observed these rays from various angles, I believe that they are the result of a process of concentrating a terrific heat into a very small area. Assuming that such an enormous pressure as 50,000,000 pounds per square inch could be concentrated in a tiny cylinder comprising an interior area of six square inches; then the force of heat at, say 50,000 degrees centigrade, would doubtlessly, when released, create a beam of such intensity as to destroy almost anything in its path for the duration of its power.

"Perhaps few who beheld the creatures when they appeared on the Surface had the presence of mind to study them thoroughly. Around the body of each were metallic belts, containing a number of concentrated heat cartridges! These, like our gun-cartridges, could be inserted in their ray-pistol chambers and their contents released probably by some form of a trigger.

"You are aware that any form of life living under such environment and conditions as the Demetrians in their Inner World, where atmosphere is totally absent, would not be required to develop the organs for breathing. In other words, they exist like a fish that has been frozen in solid ice, living without the air that we of the Surface require to exist. If the Demetrians were at one time a Surface race, they adapted themselves to the interior gradually and lost their breathing organs as the air enveloped with them was consumed. This change is no more phenomonal than the evolution of man from the lowest form of life existing at the beginning. Then as the world built up its surface crusts they made the best of the situation, and built up the domain we are observing.

"There they have remained until the present, content until they discovered that life existed on the surface probably by observing the ever deepening tools of our drilling penetrations. Then they began to object to our exploitation of what they believe to be their own resources and declared war to force us to cease. Their discovery of the Cyclops, doubtless their first Outer World expedition, taught them much about us.

"However, in trying to find a method to force them to our own terms of peace, taking into consideration their apparent immunity to death by violence, I hit upon a scheme for dissolving them with powerful gases embodying the principles of the sixth element which, as you know, is a distillation of sulphuric acid in combination with chemicals of ethereal qualities. As a result I have evolved a gas that will dissolve any organic matter coming in contact with it.

"Each of my twelve boring machines which you see racing downward will discharge their cargoes of dissolving gases within a half hour. Each tank contains twenty-four tons of the distillation or a sufficient amount of the gas to dissolve all humanity were it confined like the Demetrians. The machines are operated automatically and timed to the instant to release the gases which will circulate rapidly through the vistas and tunnels of the Inner World."

Tense, the visiting scientists in the laboratory watched the arrival of the Earth Borers in the domain of the Metal World. I chewed at my nails until blood flowed freely from the tips of my fingers, as the tanks, mere dots on the screen, entered the Metal World. They had bored through hundreds upon hundreds of miles in that short period, to reach the areas calculated to the dot of a needle point by Professor Blackton.

Finally the machines, as though controlled by one single hand, suddenly opened. Out of them poured a heavy, yellow murk that drifted swiftly through the vistas of the Demetrians. Even in the haze I could see the writhing forms of the beasts as the gases floated through thin tunnels and dissolved them into nothingness.

Virtually millions of the huge, centipede-like creatures raced along their thoroughfares to escape the oncoming destruction that now was flickering tongues of yellow into their ranks. With growing swiftness the murky haze of yellow gas penetrated into every open nook of the metal domain and gradually overtook those who sought to escape. Sick and nauseated I turned my head from the screen.

I heard the exultant shouts of the observers in the laboratory as the gases gradually wiped out the seething millions far below us. My brain crying out for me to refrain from looking again at the screen, was overcome by the thought of what might have happened to the Surface World had it not been for the unexpected achievements of Professor Blackton. Surely the Demetrians would have laid our beautiful world to ruin without an instant's hesitation. And here was the result of humanity's great desire for self preservation! When I was able to look on the screen again, the world far below had become a world deserted. No life was visible anywhere. Somehow I could not suppress a feeling of keen satisfaction that was struggling in me for release, and with a bound I reached Professor Blackton's side and grasped his hand, showering him with congratulations.

The value of Professor Blackton's great X-ray machine is now a matter of history. The world has found it invaluable. The State of California was immediately presented with the original machine by its creator after it had performed its work for the human race. And the future of the Earth Borers is already assured for many have already been built by the Federal Government as a measure for national defense. Like the submarine, the Blackton Tank, as it is now known, has become one of the most powerful implements of warfare that the world has ever known, notwithstanding the Demetrian Rays. I need not explain how Professor Blackton developed the ray, using the same principle handed to us by the destroyed scourge of the Inner World. And it is already known that Professor Blackton was greatly rewarded by each individual state and city in the nation, to say nothing of the gifts of finances made to him by the Federal Government. Those funds, as everyone knows, went for the advancement of science as only the famous gentleman understands it.

The End