"Confound you," said Langley in a hoarse whisper that came with effort through swollen lips, blue-black with thirst. "You've gulped about twice your share of the last water in the Lob-nor Desert." He shook the canteen which Furnham had just returned to him, and listened with a savage frown to the ominously light gurgling of its contents.

The two surviving members of the Furnham Archaeological Expedition eyed each other with new-born but rapidly growing disfavor. Furnham, the leader, flushed with dark anger beneath his coat of deepening dust and sunburn. The accusation was unjust, for he had merely moistened his parched tongue from Langley's canteen. His own canteen, which he had shared equally With his companion, was now empty.

Up to that moment the two men had been the best of friends. Their months of association in a hopeless search for the ruins of the semi-fabulous city of Kobar had given them abundant reason to respect each other. Their quarrel sprang from nothing else than the mental distortion and morbidity of sheer exhaustion, and the strain of a desperate predicament. Langley, at times, was even growing a trifle light-headed after their long ordeal of wandering on foot through a land without wells, beneath a sun whose flames poured down upon them like molten lead.

"We ought to reach the Tarim River pretty soon," said Furnham stiffly, ignoring the charge and repressing a desire to announce in mordant terms his unfavorable opinion of Langley.

"If we don't, I guess it will be your fault," the other snapped. "There's been a jinx on this expedition from the beginning; and I shouldn't wonder if the jinx were you. It was your idea to hunt for Kobar anyway. I've never believed there was any such place."

Furnham glowered at his companion, too near the breaking point himself to make due allowance for Langley's nerve-wrought condition, and then turned away, refusing to reply. The two plodded on, ignoring each other with sullen ostentatiousness.

The expedition, consisting of five Americans in the employ of a New York museum, had started from Khotan two months before to investigate the archaeological remains of Eastern Turkestan. Ill-luck had dogged them continually; and the ruins of Kobar, their main objective, said to have been built by the ancient Uighurs, had eluded them like a mirage. They found other ruins, had exhumed a few Greek and Byzantine coins, and a few broken Buddhas, but nothing of much novelty or importance, from a museum viewpoint.

At the very outset, soon after leaving the oasis of Tchertchen, one member of the party had died from gangrene caused by the vicious bite of a Bactrian camel. Later on, a second, seized by a cramp while swimming in the shallow Tarim Kver, near the reedy marshes of Lob-nor, that strange remnant of a vast inland sea, had drowned before his companions could reach him. A third had died of some mysterious fever. Then in the desert south of the Tarim, where Furnham and Langley still persisted in a futile effort to locate the lost city, their Mongol guides had deserted them. They took all the camels and most of the provisions, leaving to the two men only their rifles, their canteens, their other personal belongings, the various antique relics they had amassed, and a few tins of food.

The desertion was hard to explain, for the Mongols had heretofore shown themselves reliable enough. However, they had displayed a queer reluctance on the previous day, had seemed unwilling to venture further among the endless undulations of coiling sand and pebbly soil.

Furnham, who knew the language better than Langley, had gathered that they were afraid of something, were deterred by superstitious legends concerning this portion of the Lob-nor Desert. But they had been strangely vague and reticent as to the object of their fear; and Furnham had learned nothing of its actual nature.

Leaving everything but their food, water and rifles to the mercy of the drifting sands, the men had started northward toward the Tarim, which was sixty or seventy miles away. If they could reach it, they would find shelter in one of the sparse settlemeats of fishermen along its shores; and could eventually make their way back to civilization.

It was now afternoon of the second day of their wanderings. Langley had suffered most, and he staggered a little as they went on beneath the eternally cloudless heavens, across the glaring desolation of the dreary landscape. His heavy Winchester had become an insufferable burden, and he had thrown it away in spite of the remonstrance of Furnham, who still retained his own weapon.

The sun had lowered a little, but burned with gruelling rays, tyrannically torrid, through the bright inferno of stagnant air. There was no wind, except for brief and furious puffs that whirled the light sand in the faces of the men, and then died as suddenly as they had risen. The ground gave back the heat and glare of the heavens in shimmering, blinding waves of refraction.

Langley and Furnham mounted a low, gradual ridge and paused in sweltering exhaustion on its rocky spine. Before them was a broad, shallow valley, at which they stared in a sort of groggy wonderment, puzzled by the level and artificial-looking depression, perfectly square, and perhaps a third of a mile wide, which they descried in its center. The depression was bare and empty with no sign of ruins, but was lined with numerous pits that suggested the ground-plan of a vanished city.

The men blinked, and both were prompted to rub their eyes as they peered through flickering heatwaves; for each had received a momentary impression of flashing light, broken into myriad spires and columns, that seemed to fill the shallow basin and fade like a mirage.

Still mindful of their quarrel, but animated by the same unspoken thought, they stared down the long declivity, heading straight towmd the depression. If the place were the site of some ancient city they might possibly hope to find a well or water-spring.

They approached the basin's edge, and were puzzled more and more by its regularity. Certainly it was not the work of nature; and it might have been quarried yesterday, for seemingly there were no ravages of wind and weather in the sheer walls; and the floor was remarkably smooth, except for the multitude of square pits that ran in straight, intersecting lines, like the cellars of destroyed or unbuilt houses. A growing sense of strangeness and mystery troubled the two men; and they were blinded at intervals by the flash of evanescent light that seemed to overflow the basin with phantom towers and pillars.

They paused within a few feet of the edge, incredulous and bewildered. Each began to wonder if his brain had been affected by the sun. Their sensations were such as might mark the incipience of delirium. Amid the blasts of furnace-like heat, a sort of icy coolness appeared to come upon them from the broad basin. Clammy but refreshing, like the chill that might emanate from walls of sunless stone, it revived their fainting senses and quickened their awareness of unexplained mystery.

The coolness became even more noticeable when they reached the very verge of the precipice. Here, peering over, they saw that the sides fell unbroken at all ponts for a depth of twenty feet or more. In the smooth bottom, the cellar-like pits yawned darkly and unfathomably. The floor about the pits was free of sand, pebbles or detritus.

"Heavens, what do you make of that?" muttered Furnham to himself rather than to Langley. He stooped over the edge, staring down with feverish and inconclusive speculations. The riddle was beyond his experience — he had met nothing like it in all his researches. His puzzlement, however, was partly submerged in the more pressing problem of how he and Langley were to descend the sheer walls. Thirst — and the hope of finding water in one of the pits — were more important at that moment than the origin and nature of the square basin.

Suddenly, in his stooping position, a kind of giddiness seized him, and the earth seemed to pitch deliriously beneath his feet. He staggered, he lost his balance, and fell forward from the verge.

Half-fainting, he closed his eyes against the hurtling descent and the crash twenty feet below. Instantly, it seemed, he struck bottom, Amazed and incomprehending, he found that he was lying at full length, prone on his stomach in mid-air, upborne by a hard, flat, invisible substance. His outflung hands encountered an obstruction, cool as ice and smooth as marble; and the chill of it smote through his clothing as he lay gazing down into the gulf. Wrenched from his grasp by the fall, his rifle hung beside him.

He heard the startled cry of Langley, and then realized that the latter had seized him by the ankles and was drawing him back to the precipice. He felt the unseen surface slide beneath him, level as a concrete pavement, glib as glass. Then Langley was helping him to his feet. Both, for the nonce, had forgotten their misunderstanding.

"Say, am I bughouse?" cried Langley. "I thought you were a goner when you fell. What have we stumbled on, anyhow?"

"Stumbled is good," said Furnham reflectively as he tried to collect himself. "That basin is floored with something solid, but transparent as air — something unknown to geologists or chemists. God knows what it is, or where it came from or who put it there. We've found a mystery that puts Kobar in the shade. I move that we investigate."

He stepped forward, very cautiously, still half-fearful of falling, and stood suspended over the basin.

"If you can do it, I guess I can," said Langley as he followed. With Furnham in the lead, the two began to cross the basin, moving slowly and gingerly along the invisibIe pavement. The sensation of peering down as if through empty air was indescribably weird.

They had started midway between two rows of the dark pits, which lay fifty feet apart. Somehow, it was like following a street. After they had gone some little distance from the verge, Furnham deviated to the left, with the idea of looking directly down into one of these mysterious pits. Before he could reach a vertical vantage-point, he was arrested by a smooth, solid wall, like that of a building.

"I think we've discovered a city," he announced. Groping his way along the air-clear wall, which seemed free of angles or roughness, he came to an open doorway. It was about five feet wide and of indeterminable height. Fingering the wall like a blind man, he found that it was nearly six inches thick. He and Langley entered the door, still walking on a level pavement, and advanced without obstruction, as if in a large empty room.

For an instant, as they went forward, light seemed to flash above them in great arches and arcades, touched with evanescent colors like those in fountain-spray. Then it vanished, and the sun shone down as before from a void and desert-heaven. The coolness emanating from the unknown substance was more pronounced than ever; and the men almost shivered. But they were vastly refreshed, and the torture of their thirst was somewhat mitigated.

Now they could look perpendicularly into the square pit below them in the stone floor of the excavation. They were unable to see its bottom, for it went down into shadow beyond the westering sun-rays. But both could see the bizarre and inexplicable object which appeared to float immobile in air just below the mouth of the pit. They felt a creeping chill that was more insidious, more penetrant than the iciness of the unseen walls.

"Now I'm seeing things," said Langley.

"Guess I'm seeing them too," added Furnham.

The object was a long, hairless, light-grey body, lying horizontally, as if in some invisible sarcophagus or tomb. Standing erect, it would have been fully seven feet in height. It was vaguely human in its outlines, and possessed two legs and two arms; but the head was quite unearthly. The thing seemed to have a double set of high, concave ears, lined with perforations; and in place of nose, mouth and chin, there was a long, tapering trunk which lay coiled on the bosom of the monstrosity like a serpent. The eyes — or what appeared to be such — were covered by leathery, lashless and hideously wrinkled lids.

The thing lay rigid; and its whole aspect was that of a well-perserved corpse or mummy. Half in light and half in shadow, it hung amid the funereal, fathomless pit; and beneath it, at some little distance, as their eyes became accustomed to the gloom, the men seemed to perceive another and similar body.

Neither could voice the mad, eerie thoughts that assailed them. The mystery was too macabre and overwhelming and impossible. It was Langley who spoke at last.

"Say, do you suppose they are all dead?"

Before Furnham could answer, he and Langley heard a thin, shrill, exiguous sound, like the piping off some unearthly flute whose notes were almost beyond human audition. They could not determine its direction; for it seemed to come from one side and then from another as it continued. Its degree of apparent nearness or distance was also variable. It went on ceaselessly and monotonously, thrilling them with an eeriness as of untrod worlds, a terror as of uncharted dimensions. It seemed to fade away in remote ultramundane gulfs; and then, louder and clearer than before, the piping came from the air beside them.

Inexpressibly startled, the two men stared from side to side in an effort to locate the source of the sound. They could find nothing. The air was clear and still about them; and their view of the rocky slopes that rimmed the basin was blurred only by the dancing haze of heat.

The piping ceased, and was followed by a dead, uncanny silence. But Furnham and Langley had the feeling that someone or something was near them — a stealthy presence that lurked and crouched and drew closer till they could have shrieked aloud with the terror of suspense. They seemed to wait amid the unrealities of delirium and mirage, haunted by some elusive, undeclared horror.

Tensely they peered and listened, but there was no sound or visual ostent. Then Langfey cried out, and fell heavily to the unseen floor, borne backward by the onset of a cold and tangible thing, resistless as the launching coils of an anaconda. He lay helpless, unable to move beneath the dead and fluid weight of the unknown incubus, which crushed down his limbs and body and almost benumbed him with an icy chill as of etheric space. Then something touched his throat, very lightly at first, and then with a pressure that deepened intolerably to a stabbing pain, as if he had been pierced by an icicle.

A black faintness swept upon him, and the pain seemed to recede as if the nerves that bore it to his brain were spun like lengthening gossamers across gulfs of anesthesia.

Furnham, in a momentary paralysis, heard the cry of his companion, and saw Langley fall and struggle feebly, to lie inert with closing eyes and whitening face, Mechanically, without realizing for some moments what had happened, he perceived that Langley's garments were oddly flattened and pressed down beneath an invisible weight. Then, from the hollow of Langley's neck, he saw the spurting of a thin rill of blood, which mounted straight in air for several inches, and vanished in a sort of red mist.

Bizarre, incoherent thoughts arose in Furnham's mind. It was all too incredible, too unreal. His brain must be wandering, it must have given way entirely... bot something was attacking Langley — an invisible vampire of this invisible city.

He had retained his rifle. Now he stepped forward and stood beside the fallen man. His free hand, groping in the air, encountered a chill, clammy surface, rounded like the back of a stooping body. It numbed his fingertips even as he touched it. Then something seemed to reach out like an arm and hurl him violently backward.

Reeling and staggering, he managed to retain his balance and returned more cautiously. The blood still rose in a vanishing rill from Langley's throat. Estimating the position of the unseen attacker, Furnham raised his rifle and took careful aim, with the muzzle less than a yard away from its hidden mark.

The gun roared with deafening resonance, and its sound died away in slow echoes, as if repeated by a maze of walls. The blood ceased to rise from Langley's neck, and fell to a natural trickle. There was no sound, no manifestation of any kind from the thing that had assailed him. Furnham stood in doubt, wondering if his shot had taken effect. Perhaps the thing had been frightened away, perhaps it was still close at hand, and might leap upon him at any moment, or return to its prey.

He peered at Langley, who lay white and still. The blood was ceasing to flow from the tiny puncture. He stepped toward him, with the idea of trying to revive him, but was arrested by a strange circumstance. He saw that Langley's face and upper body were blurred by a grey mist that seemed to thicken and assume palpable outlines. It darkened apace, it took on solidity and form; and Furnham beheld the monstrous thing that lay prone between himself and his companion, with part of its fallen bulk still weighing upon Langley. From its inertness, and the bullet-wound in its side, whence oozed a viscid purple fluid, he felt sure that the thing was dead.

The monster was alien to all terrestrial biology — a huge, invertebrate body, formed like an elongated starfish, with the points ending in swollen tentacular limbs. It had a round, shapeless head with the curving, needle-tipped bill of some mammoth insect. It must have come from other planets or dimensions than ours. It was wholly unlike the mummified creature that floated in the pit below, and Furnham felt that it represented an inferior animal-like type. lt was evidently composed of an unknown order of organic matter that became visible to human eyes only in death.

His brain was swamped by the mad enigma of it all; What was this place upon which he and Langley had stumbled? Was it an outpost of worlds beyond human knowledge or observation? What was the material of which these buildings had been wrought? Who were their builders? Whence had they come and what had been their purpose? Was the city of recent date or was it, perhaps, a sort of ruin, whose builders lay dead in its vaults — a ruin haunted only by the vampire monster that had assailed Langley?

Shuddering with repulsion at the dead monster, he started to drag the still-unconscious man from beneath the loathsome mass. He avoided touching the dark, semi-translucent body, which lapsed forward, quivering like a stiff jelly when he had pulled his companion away from it.

Like something very trivial and far away, he remembered the absurd quarrel which Langley had picked with him, and remembered his own resentment as part of a doubtful dream, now lost in the extra-human mystery of their surroundings. He bent over his comrade, anxiously, and saw that some of the natural tan was returning to the pale face and that the eyelids were begging to flutter. The blood had clotted on the tiny wound. Taking Langley's canteen, he poured the last of its contents between the owner's teeth.

In a few moments Langley was able to sit up. Furnham helped him to his feet, and the two began to cross their way from the crystal maze.

They found the doorway; and Furnham, still supporting the other, decided to retrace their course along the weird street by which they had started to cross the basin. They had gone but a few paces when they heard a faint, almost inaudible rustling in the air before them, together with a mysterious grating noise. The rustling seemed to spread and multiply on every hand, as if an invisible crowd were gathering; but the grating soon ceased.

They went on, slowly and cautiously, with a sense of imminent, uncanny peril. Langley was now strong enough to walk without assistance; and Furnham held his cocked rifle ready for instant use. The vague rustling sounds receded, but still encircled them.

Midway between the underlying rows of pits, they moved on toward the desert precipice, keeping side by side. A dozen paces on the cold, solid pavement, and then they stepped into empty air and landed several feet below with a terrific jar, on another hard surface.

It must have been the top of a flight of giant stairs; for, losing their balance, they both lurched and fell, and rolled downward along a series of similar surfaces, and lay stunned at the bottom.

Langley had been rendered unconscious by the fall; but Fornham was vaguely aware of several strange, dreamlike phenomena. He heard a faint, ghostly, sibilant rustling, he felt a light and clammy touch upon his face, and smelled an odor of suffocating sweetness, in which he seemed to sink as into an unfathomable sea. The rustling died to a vast and spatial silence; oblivion darkened above him; and he slid swiftly into nothingness.

It was night when Furnham awoke. His first impression was the white dazzle of a full moon shining in his eyes. Then he became aware that the circle of the great orb was oddly distorted and broken, like a moon in some cubistic painting. All around and above him were bright, crystalline angles, crossing and intermingling -the outlines of a translucent architecture, dome on dome and wall on wall. As he moved his head, showers of ghostly irises — the lunar yellow and green and purple -- fell in his eyes from the broken orb and vanished.

He saw that he was lying on a glass-like floor, which caught the light in moving sparkles. Langley, still unconscious, was beside him. Doubtless they were still in the mysterious oubliette down whose invisible stairs they had fallen. Far off, to one side, through a mélange of the transparent partitions, he could see the vague rocks of the Gobi, twisted and refracted in the same manner as the moon.

Why, he wondered, was the city now visible? Was its substance rendered perceptible, in a partial sort of way, by some unknown ray which existed in moonlight but not in the direct beams of the sun? Such an explanation sounded altogether too unscientific; but he could not think of any other at the moment.

Rising on his elbow, he saw the glassy outlines of the giant stairs down which he and Langley had plunged. A pale, diaphanous form, like a phantom of the mummified creature they had seen in the pit, was descending the stairs. It moved forward with fleet strides, longer than those of a man, and stooped above Furnham with its spectral trunk waving inquisitively and poising an inch or two from his face. Two round, phosphorescent eyes, emitting perceptible beams like lanterns, glowed solemnly in its head above the beginning of the proboscis.

The eyes seemed to transfix Furnham with their unearthly gaze. He felt that the light they emitted was flowing in a ceaseless stream into his own eyes — into his very brain. The light seemed to shape itself into images, formless and incomprehensible at first, but growing clearer and more coherent momently. Then, in some indescribable way, the images were associated with articulate words, as if a voice were speaking: words that he understood as one might understand the language of dreams.

"We mean you no harm," the voice seemed to say. "But you have stumbled upon our city; and we cannot afford to let you escape. We do not wish to have our presence known to men.

"We have dwelt here for many ages, The Lob-nor desert was a fertile realm when we first established our city. We came to your world as fugitives from a great planet that once formed part of the solar system — a planet composed entirely of ultra-violet substances, which was destroyed in a terrible cataclysm. Knowing the imminence of the catastrophe, some of us were able to build a huge space-flier, in which we fled to the Earth. From the materials of the flier, and other materials we had brought along for the express purpose, we built our city, whose name, as well as it can be conveyed in human phonetics, is Ciis.

"The things of your world have always been plainly visible to us; and, in fact, due to our immense scale of perceptions, we probably see much that is not manifest to you. Also, we have no need of artificial light at any time. We discovered, however, at an early date, that we ourselves and our buildings were invisible to men. Strangely enough, our bodies undergo in death a degeneration of substance which brings them within the infra-violet range; and thus within the scope of your visual cognition."

The voice seemed to pause, and Furnham realized that it had spoken only in his thought by a sort of telepathy. In his own mind, he tried to shape a question:

"What do you intend to do with us?"

Again he heard the still, toneless voice:

"We plan to keep you with us permanently. After you fell through the trap-door we had opened, we overpowered you with an anesthetic; and during your period of unconsciousness, which lasted many hours, we injected into your bodies a drug which has already affected your vision, rendering visible, to a certain degree, the ultra-violet substances that surround you. Repeated injections, which must be given slowly, will make these substances no less plain and solid to you than the materials of your own world. Also, there are other processes to which we intend to subject you... processes that will serve to adjust and acclimate you in all ways to your new surroundings."

Behind Furnham's weird interlocutor, several more fantasmal figures had descended the half-visible steps. One of them was stooping over Langley, who had begun to stir and would recover full consciousness in a few instants. Furnham sought to frame other questions, and received an immediate reply.

"The creature that attacked your companion was a domestic animal. We were busy in our laboratories at the time, and did not know of your presence till we heard the rifle shots.

"The flashes of light which you saw among our invisible walls on your arrival were due to some queer phenomenon of refraction. At certain angles the sunlight was broken or intensified by the molecular arrangement of the unseen substance."

At this juncture Langley sat up, looking about him in a bewildered fashion.

"What the hell is all this, and where the hell are we?" he inquired as he peered from Furnham to the people of the city.

Furnham proceeded to explain, repeating the telepathic information he had just received. By the time he had ceased speaking, Langley himself appeared to become the recipient of some sort of mental reassurance from the phantom-like creature who had been Furnham's interlocutor; for Langley stared at this being with a mixture of enlightenment and wonder in his expression.

Once more there came the still, super-auditory voice, fraught now with imperious command.

"Come with us. Your initiation into our life is to begin immediately. My name is Aispha — if you wish to have a name for me in your thoughts. We ourselves, communicating with each other without language, have little need for names; and their use is a rare formality among us. Our generic name, as a people, is the Tiisins."

Furnham and Langley arose with an unquestioning alacrity, for which afterwards they could hardly account, and followed Aispha. It was as if a mesmeric compulsion had been laid upon them. Furnham noted, in an automatic sort of way, as they left the oubliette, that his rifle had vanished. No doubt it had been carefully removed during his period of insensibility.

He and Langley climbed the high steps with some difficulty. Queerly enough, considering their late fall, they found themselves quite free of stiffness and bruises; but at the time they felt no surprise — only a drugged acquiescence in all the marvels and perplexities of their situation.

They found themselves on the outer pavement, amid the bewildering outlines of the luminous buildings which towered above them with intersections of multiform crystalline curves and angles. Aispha went on without pause, leading them toward the fantastic serpentine arch of an open doorway in one of the tallest of these edifices, whose pale domes and pinnacles were heaped in immaterial splendor athwart the zenith-nearing moon.

Four of the ultra-violet people — the companions of Aispha — brought up the rear. Aispha was apparently unarmed; but the others carried weapons like heavybladed and blunt-pointed sickles of glass or crystal Many others of this incredible race, intent on their own enigmatic affirs, were passing to and fro in the open street and through the portals of the unearthly buildings. The city was a place of silent and fantasmal activity.

At the end of the street they were following, before they passed through the arched entrance, Furnham and Langley saw the rock-strewn slope f the Lob-nor, which seemed to have taken on a queer filminess and insubstantiality in the moonlight. It occurred to Furnham, with a sort of weird shock, that his visual perception of earthly objects, as well as of the ultra-violet city, was being affected by the injections of which Aispha told him.

The building they now entered was full of apparatuses made in the form of distorted spheres and irregular disks and cubes, some of which seemed to change their outlines from moment to moment in a confusing manner. Certain of them appeared to concentrate the moonlight like ultra-powerful lenses, turning it to a fiery, blinding brilliance. Neither Furnham nor Langley could imagine the purpose of these devices; and no telepathic explanation was vouchsafed by Aispha or any of his companions.

As they went on into the building there was a queer sense of some importunate and subtle vibration in the air, which affected the men unpleasantly. They could not assign its source nor could they be sure whether their own perception of it was purely mental or came through the avenues of one or more of the physical senses. Somehow it was both disturbing and narcotic; and they sought instinctively to resist its influence.

The lower story of the edifice was seemingly one vast room. The strange apparatuses grew taller about them, rising as if in concentric tiers as they went on. In the huge dome above them, living rays of mysterious light appeared to cross and re-cross at all angles of incidence, weaving a bright, ever-changing web that dazzled the eye.

They emerged in a clear, circular space at the center of the building. Here ten or twelve of the ultra-violet people were standing about a slim column, perhaps five feet high, that culminated in a shallow basin-like formation. There was a glowing oval-shaped object in the basin, large as the egg of some extinct bird. From this object, numerous spokes of light extended horizontally in all directions, seeming to transfix the heads and bodies of those who stood in a loose ring about the column. Furnham and Langley became aware of a high, thin, humming noise which emanated from the glowing egg and was somehow inseparable from the spokes of light, as if the radiance had become audible.

Aispha paused facing the men; and a voice spoke in their minds.

"The glowing object is called the Doir. An explanation of its real nature and origin would be beyond your present comprehension. It is allied, however, to that range of substances which you would classify as minerals; and is one of a number of similar objects which existed in our former world. It generates a mighty force which is intimately connected with our life-principle; and the rays emanating from it serve us in place of food. If the Doir were lost or destroyed, the consequences would be serious; and our life-term, which normally is many thousand years, would be shortened for want of the nourishing and revivifying rays."

Fascinated, Furnham and Langley stared at the eggshaped orb. The humming seemed to grow louder; and the spokes of light lengthened and increased in number. The men recognized it now as the source of the vibration that had troubled and oppressed them. The effect was insidious, heavy, hypnotic, as if there were a living brain in the object that sought to overcome their volition and subvert their senses and their minds in some unnatural thralldom.

They heard the mental command of Aispha:

"Go forward and join those who partake of the luminous emanations of the Doir. We believe that by so doing you will, in course of time, become purged of your terrestrial grossness; that the very substance of your bodies may eventually be transformed into something not unlike that of our own; and your senses raised to a perceptional power such as we possess."

Half unwillingly, with an eerie consciousness of compulsion, the men started forward.

"I don't like this," said Furnham in a whisper to Langley. 'I'm beginning to feel queer enough already." Summoning his utmost will power he stopped short of the emanating rays and put out his hand to arrest Langley.

With dazzled eyes, they stood peering at the Doir. A cold, restless fire, alive with some nameless evil that was not akin to the evil of Earth, pulsated in its heart; and the long, sharp beams, quivering slightly, passed like javelins into the semi-crystalline bodies of the beings who stood immobile around the column.

"Hasten!" came the unvocal admonition of Aispha. "In a few moments the force in the Doir, which has a regular rhythm of ebb and flow, will begin to draw back upon itself. The rays will be retracted; and you will have to wait for many minutes before the return of the emanation."

A quick, daring thought had occurred to Furnham. Eyeing the Doir closely, he had been impressed by its seeming fragility. The thing was evidently not attached to the basin in which it reposed; and in all likelihood it would shatter like glass if hurled or even dropped on the floor. He tried to suppress his thought, fearing that it would be read by Aispha or others of the ultra-violet people. At the same time, he sought to phrase, as innocently as possible, a mental question:

"What would happen if the Doir were broken?"

Instantly he received an impression of anger, turmoil and consternation in the mind of Aispha. His question, however, was apparently not answered; and it seemed that Aispha did not want to answer it — that he was concealing something too dangerous and dreadful to be revealed. Furnham felt, too, that Aispha was suspicious, had received an inkling of his own repressed thought.

It occurred to him that he must act quickly if at all. Nerving himself, he leaped forward through the ring of bodies about the Doir. The rays had already begun to shorten slightly; but he had the feeling of one who hurls himself upon an array of lance-points. There was an odd, indescribable sensation, as if he were being pierced by something that was both hot and cold; but neither the warmth nor the chill was beyond endurance. A moment, and he stood beside the column, lifting the glowing egg in his hands and poising it defiantly as he turned to face the ultra-violet people.

The thing was phenomenally light; and it seemed to burn his fingers and to freeze them at the same time. He felt a strange vertigo, an indescribable confusion; but he succeeded in mastering it. The contact of the Doir might be deadlier to the human tissues than that of radium for aught he knew. He would have to take his chances. At any rate it would not kill him immediately; and if he played his cards with sufficient boldness and skill, he could make possible the escape of Langley -- if not his own escape.

The ring of ultra-violet beings stood as if stupefied by his audacity. The retracting spokes of light were slowly drawing back into the egg; but Furnham himself was still impaled by them. His fingers seemed to be growing translucent where they clutched the weird ball.

He met the phosphoric gaze of Aispha, and heard the frantic thoughts that were pouring into his mind, not only from Aispha but from all the partakers of the Doir's luminous beams. Dread, unhuman threats, desperate injunctions to return the Doir to its pedestal, were being laid upon him. Rallying all his will, he defied them.

"Let us go free," he said, mentally addressing Aispha. "Give me back my weapon and permit my companion and me to leave your city. We wish you no harm; but we cannot allow you to detain us. Let us go or I will shatter the Doir — will smash it like an egg on the floor."

At the shaping of his destructive thought, a shudder passed among the semi-spectral beings; and he felt the dire fear that his threat had aroused in them. He had been right: the Doir was fragile; and some awful catastrophe, whose nature he could not quite determine, would ensue instantly upon its shattering.

Step by step, glancing frequently about to see that no one approached him by stealth from behind, Furnham returned to Langley's side. The Tiisins drew back from him in evident terror. All the while he continued to issue his demands and comminations:

"Bring the rifle quickly... the weapon you took from me... and give it into my companion's hands. Let us go without hindrance or molestation — or I will drop the Doir. When we are outside the city, one of you — one only — shall be permitted to approach us, and I will deliver the Doir to him."

One of the Tiisins left the group to return in less than a minute with Furnham's Winchester. He handed it to Langley, who inspected the weapon carefully and found that it had not been damaged or its loading or mechanism tampered with in any way. Then, with the ultra-violet creatures following them in manifest perturbation, Furnham and Langley made their way from the building and started along the open street in the general direction (as Langley estimated from the compass he carried) of the Tarim River.

They went on amid the fantastic towering of the crystalline piles; and the people of the city, called as if by some unworded summons, poured from the doorways in an ever-swelling throng and gathered behind them There was no active demonstration of any overt kind; but both the men were increasingly aware of the rage and consternation that had been aroused by Furnham's audacious theft of the Doir — a theft that seemed to be regarded in the light of actual blasphemy.

The hatred of the Tiisins, like a material radiation -dark, sullen, stupefying, stultifying, beat upon them at every step. It seemed to dog their brains and their feet like some viscid medium of nightmare; and their progession toward the Gobi slope became painfully slow and tedious.

Before them, from one of the buildings, a tentacled, starfish monster, like the thing that had assailed Langley, emerged and lay crouching in the street as if to dispute their passage. Raising its evil beak, it glared with filmy eyes, but slunk away from their approach as if at the monition of its owners.

Furnham and Langley, passing it with involuntary shivers of repugnance, went on. The air was oppressed with alien, unformulable menace. They felt an abnormal drowsiness creeping upon them. There was an unheard, narcotic music, which sought to overcome their vigilance, to beguile them into slumber.

Furnham's fingers grew numb with the unknown radiations of the Doir, though the sharp beams of light, by accelerative degrees, had withdrawn into its center, leaving only a formless misty glow that filled the weird orb. The thing seemed latent with terrible life and power. The bones of his transparent hand were outlined against it like those of a skeleton.

Looking back, he saw that Aispha followed closely, walkiag in advance of the other Tiisins. He could not read the thoughts of Aispha as formerly. It was as if a blank, dark wall had been built up. Somehow he had a premonition of evil — of danger and treachery in some form which he could not understand or imagine.

He and Langley came to the end of the street, where the ultra-violet pavement joined itself to the desert acclivity. As they began their ascent of the slope both men realized that their visual powers had indeed been affected by the injection treatment of the Tiisins; for the soil seemed to glow beneath them, faintly translucent; and the boulders were like semi-crystalline masses, whose inner structure they could see dimly.

Aispha followed them on the slope; but the other people of Ciis, as had been stipulated by Furnham, paused at the juncture of their streets and buildings with the infra-violet substances of Earth.

After they had gone perhaps fifty yards on the gentle acclivity, Furnham came to a pause and waited for Aispha, hoIding out the Doir at arm's length. Somehow he had a feeling that it was unwise to return the mystic egg; but he would keep his promise, since the people of Ciis had kept their part of the bargain so far.

Aispha took the Doir from Furnham's hands; but his thoughts, whatever they were, remained carefully shrouded. There was a sense of something ominous and sinister about him as he turned and went back down the slope with the fiery egg shining through his body like a great watchful eye. The beams of light were beginning to emanate from its center once more. The two men, looking back ever and anon, resumed their journey. Ciis glimmered below them like the city of a mirage in the moonlit hollow. They saw the ultraviolet people crowding to await Aispha at the end of their streets.

Then, as Aispha neared his fellows two rays of cold, writhing fire leaped forth from the base of a tower that glittered like glass at the city's verge. Clinging to the ground, the rays ran up the slope with the undulant motion of pythons, following Langley and Furnham at a speed that would soon overtake them.

"They're double crossing us!" warned Furnham. He caught the Winchester from Langley, dropped to his knees and aimed carefully, drawing a bead on the luminous orb of the Doir through the spectral form of Aispha, who had now reached the city and was about to enter the waiting throng.

"Run!" he called to Langley. "I'll make them pay for their treachery; and perhaps you can get away in the meanwhile."

He pulled the trigger, missing Aispha but dropping at least two of the Tiisins who stood near the Doir. Again, steadily, he drew bead, while the rays from the tower serpentined onward, pale, chill and deadly-looking, till they were almost at his feet. Even as he aimed, Aispha took refuge in the foremost ranks of the crowd, through whose filmy bodies the Doir still glowed.

This time the high-powered bullet found its mark, though it must have passed through more than one of the ultra-violet beings before reaching Aispha and the mystic orb.

Furnham had hardly known what the result would be, but he felt sure that some sort of catastrophe would ensue the destruction of the Doir. What really happened was incalculable and almost beyond description. Before the Doir could fall from the hands of its stricken bearer, it seemed to expand in a rushing wheel of intense light, revolving as it grew, and blotting out the form of the ultra-violet people in the foreground. With awful velocity, the wheel struck the nearer buildings, which appeared to soar and vanish like towers of fading mirage. There was no audible explosion — no sound of any kind — only that silent, ever-spinning, ever-widening disk of light that threatened to involve by swift degrees the whole extent of Ciis.

Gazing spellbound, Furnham had almost forgotten the serpentine rays. Too late he saw that one of them was upon him. He leaped back, but the thing caught him, coiling about his limbs and body like an anaconda. There was a sensation of icy cold, of horrible constriction; and then, helpless, he found that the strange beam of force was dragging him back down the slope toward Ciis, while its fellow went on in pursuit of the fleeing Langley.

In the meanwhile the spreading disk of fire had reached the tower from which the ray emanated. Suddenly, Furnham was free — the serpentine beams had both vanished. He stood rooted to the spot in speechless awe; and Langley, returning down the hill, also paused, watching the mighty circle of light that seemed to fill the entire basin at their feet with a soundless vortex of destruction.

"My God!" cried Furnham after a brief interval. "Look what's happening to the slope."

As if the force of the uncanny explosion were now extending beyond Ciis, boulders and masses of earth began to rise in air before the white, glowing maelstron, and sailed in slow, silent levitation toward the men.

Furnham and Langley started to run, stumbling up the slope, and were overtaken by something that lifted them softly, buoyantly, irresistibly, with a strange feeling of utter weightlessness, and bore them like windwafted leaves or feathers through the air. They saw the bouldered crest of the acclivity flowing far beneath them; and then they were floating, floating, ever higher in the moonlight, above leagues of dim desert. A faintness came upon them both — a vague nausea — an illimitable vertigo; and slowly, somewhere in that incredible flight, they lapsed into unconsciousness.

The moon had fallen low, and its rays were almost horizontal in Furnham's eyes when he awoke. An utter confusion possessed him at first; and his circumstances were more than bewildering. He was lying on a sandy slope, among scattered shrubs, meager and stunted; and Langley was reclining not far away. Raising himself a little, he saw the white and reedfringed surface of a river — which could be no other than the Tarim — at the slope's bottom. Half incredulous, he realized that the force of the weird explosion had carried Langley and himself many miles and had deposited them, apparently unhurt, beside the goal of their desert wandering!

Furnham rose to his feet, feeling a queer lightness and unsteadiness. He took a tentative step — and landed four or five feet away. It was as if he had lost half his normal weight. Moving with great care he went over to Langley, who had now started to sit up. He was reassured to find that his eye-sight was becoming normal again; for he perceived merely a faint glowing in the objects about him. The sand and boulders were comfortably solid; and his own hands were no longer translucent.

"Gosh!" he said to Langley, "That was some explosion. The force that was liberated by the shattering of the Doir must have done something to the gravity of all surrounding objects. I guess the city of Ciis and its people must have gone back into outer space; and even the infra-violet substances about the city must have been more or less degravitated. But I guess the effect is wearing off as far as you and I are concerned -otherwise we'd be traveling still."

Langley got up and tried to walk, with the same disconcerting result that had characterized Furnham's attempt. He mastered his limbs and his equilibrium after a few experiments.

"I still feel like a sort of dirigible," he commented. "Say, I think we'd better leave this out of our report to the museum. A city, a people, all invisible, in the heart of the Lob-nor — that would be too much for scientific credibility."

"I agree with you," said Furnham, "the whole business would be too fantastic, outside of a super-scientific story. In fact," he added a little maliciously, "it's even more incredible than the existence of the ruins of Kobar."