Norman and Hackett, bulky in their thick flying suits, seemed to fill the little office. Across the room Harding, the field superintendent, contemplated them. Two planes were curving up into the dawn together from the field outside, their motors thunderous as they roared over the building. When their clamor had receded, Harding spoke:

“I don’t know which of you two is crazier,” he said. “You, Norman, to propose a fool trip like this, or you, Hackett, to go with him.”

Hackett grinned, but the long, lean face of Norman was earnest. “No doubt it all sounds a little insane,” he said, “but I’m convinced I’m right.”

The field superintendent shook his head. “Norman, you ought to be writing fiction instead of flying. A second satellite--and Fellows and the others on it--what the devil!”

“What other theory can account for their disappearance?” asked Norman calmly. “You know that since the new X-type planes were introduced, hundreds of fliers all over Earth have been trying for altitude records in them. Twenty-five miles--thirty--thirty-five--the records have been broken every day. But out of the hundreds of fliers who have gone up to those immense heights, four have never come down nor been seen again!

“One vanished over northern Sweden, one over Australia, one over Lower California, and one, Fellows, himself, right here over Long Island. You saw the globe on which I marked those four spots, and you saw that when connected they formed a perfect circle around the Earth. The only explanation is that the four fliers when they reached a forty-mile height were caught up by some body moving round Earth in that circular orbit, some unknown moon circling Earth inside its atmosphere, a second satellite of Earth’s whose existence has until now never been suspected!”

Harding shook his head again. “Norman, your theory would be all right if it were not for the cold fact that no such satellite has ever been glimpsed.”

“Can you glimpse a bullet passing you?” Norman retorted. “The two fliers at Sweden and Lower California vanished within three hours of each other, on opposite sides of the Earth. That means that this second satellite, as I’ve computed, circles Earth once every six hours, and travelling at that terrific speed it is no more visible to us of Earth than a rifle bullet would be.”

“Moving through Earth’s atmosphere at such speed, indeed, one would expect it to burn up by its own friction with the air. But it does not, because its own gravitational power would draw to itself enough air to make a dense little atmosphere for itself that would cling to it and shield it as it speeds through Earth’s upper air. No, I’m certain that this second satellite exists, Harding, and I’m as certain that it’s responsible for the vanishing of those four fliers.”

“And now you and Hackett have figured when it will be passing over here and are going up in an X-type yourselves to look for it,” Harding said musingly.

“Look for it?” echoed Hackett. “We’re not going to climb forty miles just to get a look at the damn thing--we’re going to try landing on it!”

“You’re crazy sure!” the field superintendent exploded. “If Fellows and those others got caught by the thing and never came down again, why in the name of all that’s holy would you two want--” He stopped suddenly. “Oh, I think I see,” he said, awkwardly. “Fellows was rather a buddy of you two, wasn’t he?”

“The best that ever flew a crippled Nieuport against three Fokkers to pull us out of a hole,” said Norman softly. “Weeks he’s been gone, and if it had been Hackett and I he’d be all over the sky looking for us--the damned lunatic. Well, we’re not going to let him down.”

“I see,” Harding repeated. Then--”Well, here comes your mechanic, Norman, so your ship must be ready. I’ll go with you. It’s an event to see two Columbuses starting for another world.”

The gray dawn-light over the flying field was flushing to faint rose as the three strode out to where the long X-type stood, its strangely curved wings, enclosed cabin and flat, fan-like tail gleaming dully. Its motor was already roaring with power and the plane’s stubby wheels strained against the chocks. In their great suits Norman and Hackett were like two immense ape-figures in the uncertain light, to the eyes of those about them.

“Well, all the luck,” Harding told them. “You know I’m pulling for you, but--I suppose it’s useless to say anything about being careful.”

“I seem to have heard the words,” Hackett grinned, as he and Norman shook the field superintendent’s hand.

“It’s all the craziest chance,” Norman told the other. “And if we don’t come down in a reasonable time--well, you’ll know that our theory was right, and you can broadcast it or not as you please.”

“I hope for your sake that you’re dead wrong,” smiled the official. “I’ve told you two to get off the Earth a lot of times, but I never meant it seriously.”

Harding stepped back as the two clambered laboriously into the cramped cabin. Norman took the controls, the door slammed, and as the chocks were jerked back and the motor roared louder the long plane curved up at a dizzy angle from the field into the dawn. Hackett waved a thick arm down toward the diminishing figures on the field below; then turned from the window to peer ahead with his companion.

The plane flew in a narrow ascending spiral upward, at an angle that would have been impossible to any ship save an X-type. Norman’s eyes roved steadily over the instrument as they rose, his ears unconsciously alert for each explosion of the motor. Earth receded swiftly into a great gray concave surface as they climbed higher and higher.

By the time the five-mile height was reached Earth’s surface had changed definitely from concave to convex. The plane was ascending by then in a somewhat wider spiral, but its climb was as steady and sure as ever. Frost begin to form quickly on the cabin’s windows, creeping out from the edges. Norman spoke a word over the motor’s muffled thunder, and Hackett snicked on the electrical radiators. The frost crept back as their warm, clean heat flooded the cabin.

Ten miles--fifteen--they had reached already altitudes impossible but a few years before, though it was nothing to the X-types. As they passed the ten-mile mark, Hackett set the compact oxygen-generator going. A clean, tangy odor filled the cabin as it began functioning. Twenty miles--twenty-two--

After a time Norman pointed mutely to the clock on the instrument board, and Hackett nodded. They were well within their time schedule, having calculated to reach the forty-mile height at ten, the hour when, by its computed orbit, the second satellite should be passing overhead. “--26--27--28--” Hackett muttered the altimeter figures to himself as the needle crept over them.

Glancing obliquely down through the window he saw that Earth was now a huge gray ball beneath them, white cloud-oceans obscuring the drab details of its surface here and there. “--31--32--” The plane was climbing more slowly, and at a lesser angle. Even the X-type had to struggle to rise in the attenuated air now about them. Only the super-light, super-powered plane could ever have reached the terrific height.

It was at the thirty-four mile level that the real battle for altitude began. Norman kept the plane curving steadily upward, handling it with surpassing skill in the rarefied air. Frost was on its windows now despite the heating mechanism. Slowly the altimeter needle crept to the forty mark. Norman kept the ship circling, its wings tilted slightly, but not climbing, Earth a great gray misty ball beneath.

“Can’t keep this height long,” he jerked. “If our second satellite doesn’t show up in minutes we’ve had a trip for nothing.”

“All seems mighty different up here,” was Hackett’s shouted comment. “Easy enough to talk down there about hopping onto the thing, but up here--hell, there’s nothing but air and mighty little of that!”

Norman grinned. “There’ll be more. If I’m right about this thing we won’t need to hop it--its own atmosphere will pick us up.”

Both looked anxious as the motor sputtered briefly. But in a moment it was again roaring steadily. Norman shook his head.

“Maybe a fool’s errand after all. No--I’m still sure we’re right! But it seems that we don’t prove it this time.”

“Going down?” asked Hackett.

“We’ll have to, in minutes. Even with its own air-feed the motor can’t stand this height for--”

Norman never finished the words. There was a sound, a keen rising, rushing sound of immense power that reached their ears over the motor’s roar. Then in an instant the universe seemed to go mad about them: they saw the gray ball of Earth and the sun above skyrocketing around them as the plane whirled madly.

The rushing sound was in that moment thunderous, terrible, and as winds smashed and rocked the plane like giant hands, Hackett glimpsed another sphere that was not the sphere of Earth, a greenish globe that expanded with lightning speed in the firmament beside their spinning plane! The winds stilled; the green globe changed abruptly to a landscape of green land and sea toward which the plane was falling! Norman was fighting the controls--land and sea were gyrating up to them with dizzy speed--crash!

With that cracking crash the plane was motionless. Sunlight poured through its windows, and great green growths were all around it. Hackett, despite Norman’s warning cry, forced the door open and was bursting outside, Norman after him. They staggered and fell, with curious lightness and slowness, on the ground outside, then clutched the plane for support and gazed stupefiedly around them.

The plane had crashed down into a thicket of giant green reeds that rose a yard over their heads, its pancake landing having apparently not damaged it. The ground beneath their feet was soft and soggy, the air warm and balmy, and the giant reeds hid all the surrounding landscape from view.

In the sky the sun burned near one horizon with unusual brilliance. But it was dwarfed, in size, by the huge gray circle that filled half the heavens overhead. A giant gray sphere it was, screened here and there by floating white mists and clouds, that had yet plain on it the outlines of dark continents and gleaming seas. A quaking realization held the two as they stared up at it.

“Earth!” Norman was babbling. “It’s Earth, Hackett--above us; my God, I can’t believe even yet that we’ve done it!”

“Then we’re on--the satellite--the second satellite!--” Hackett fought for reality. “Those winds that caught us--”

“They were the atmosphere of this world, of the second satellite! They caught us and carried us on inside this smaller world’s atmosphere, Hackett. We’re moving with it around Earth at terrific speed now!”

“The second satellite, and we on it!” Hackett whispered, incredulously. “But these reeds--it can’t all be like this--”

They stepped together away from the plane. The effort sent each of them sailing upward in a great, slow leap, to float down more than a score of feet from the plane. But unheeding in their eagerness this strange effect of the satellite’s lesser gravitational power, they moved on, each step a giant, clumsy leap. Four such steps took them out of the towering reeds onto clear ground.

It was a gentle, grassy slope they were on, stretching away along a gray-green sea that extended out to the astoundingly near horizon on their right. To the left it rose into low hills covered with dense masses of green junglelike vegetation. Hackett and Norman, though, gazed neither at sea or hills for the moment, but at the half-score grotesque figures who had turned toward them as they emerged from the reeds. A sick sense of the unreal held them as they gazed, frozen with horror. For the great figures returning their gaze a few yards from them were--frog-men!

Frog-men! Great mottled green shapes seven to eight feet in height, with bowed, powerful legs and arms that ended in webbed paws. The heads were bulbous ones in which wide, unwinking frog-eyes were set at the sides, the mouths white-lipped and white-lined. Three of the creatures held each a black metal tube-and-handle oddly like a target-pistol.

“Norman!” Hackett’s voice was a crescendo of horror. “Norman!“

“Back to the plane!” Norman cried thickly. “The plane--”

The two staggered back, but the frog-men, recovering from their own first surprise, were running forward with great hopping steps! The two fliers flung themselves back in a floating leap toward the reeds, but the green monsters were quick after them. A croaking cry came from one and as another raised his tube-and-handle, something flicked from it that burst close beside Norman. There was no sound or light as it burst, but the reeds for a few feet around it vanished!

A hoarse cry from Hackett--the creatures had reached him, grasped him at the edge of the reeds! Norman swerved in his floating leap to strike the struggling flier and frog-men. The scene whirled around him as he fought them, great paws reaching for him. With a sick, frantic rage he felt his clenched fist drive against cold, green, billowy bodies. Croaking cries sounded in his ears; then, Hackett and he were jerked to their feet, held tightly by four of the creatures.

“My God, Norman,” panted Hackett, helpless. “What are they--frog-things?--”

“Steady, Hackett. They’re the people of the second satellite, it seems; wait!”

One of the armed frog-men approached and inspected them, and then croaked an order in a deep voice. Then, still holding the two tightly, the party of monsters began to move along the slope, skirting the sea’s edge. In a few minutes they reached two curious objects resting on the slope. They seemed long black metal boats, slender and with sharp prow and stern. A compact mechanism and control-board filled the prow, while at the stern and sides were long tubes mounted on swivels like machine-guns.

The frog-men motioned Norman and Hackett into one, fastening the two prisoners and themselves into their seats with metal straps provided for the purpose. Four had entered the one boat, the others that of the captives. One at the prow moved his paws over the control-board and with a purring of power the boat, followed by the other, rose smoothly into the air. It headed out over the gray-green sea, land dropping quickly from sight behind, the horizons water-bounded on all sides. From their nearness Norman guessed that this second satellite of Earth’s was small indeed beside its mother planet. He had to look up to earth’s great gray sphere overhead to attain a sense of reality.

Hackett was whispering beside him, the frog-men watchful. “Norman, it’s not real--it can’t be real! These things--these boats--intelligent like men--”

The other sought to steady him. “It’s a different world, Hackett. Gravitation different, light different, everything different, and evolution here has had a different course. On Earth men evolved to be the most intelligent life-forms, but here the frog-races, it seems.”

“But where are they taking us? Could we ever find the plane again?”

“God knows. If we ever get away from these things we might. And we’ve got to find Fellows, too; I wonder where he is on this world.”

For many minutes the two boats raced on at great speed over the endless waters before the watery skyline was broken far ahead by something dark and unmoving. Hackett and Norman peered with intense interest toward it. It seemed at first a giant squat mountain rising from the sea, but as they shot nearer they saw that its outline was too regular, and that colossal as it was in size it was the work of intelligence. They gasped as they came nearer and got a better view of it.

For it was a gigantic dome of black metal rising sheer from the lonely sea, ten miles if anything in diameter, a third that in greatest height. There was no gate or window or opening of any kind in it. Just the colossal, smooth black dome rearing from the watery plain. Yet the two boats were flashing lower toward it.

“They can’t be going inside!” Hackett conjectured. “There’s no way in and what could be in there? The whole thing’s mad--”

“There’s some way,” Norman said. “They’re slowing--”

The flying-boats were indeed slowing as they dipped lower. They were very near the dome now, its curving wall a looming, sky-high barrier before them. Suddenly the boats dipped sharply downward toward the green sea. Before the two fliers could comprehend their purpose, could do aught more than draw instinctive great breaths in preparation, the two craft had shot down into the waters and were arrowing down through the green depths.

Blinded, flung against his metal strap by the resistance of the waters they ripped through, Norman yet retained enough of consciousness to glimpse beams of light that stabbed ahead from the prows of their rushing boats, to see vaguely strange creatures of the deep blundering in and out of those beams as the boats hurtled forward. The water that forced its way between his lips was fresh, he was vaguely aware, and even as he fought to hold his breath was aware too that the frog-men seemed in no way incommoded by the sudden transition into the water, their amphibian nature allowing them to stay under it far longer than any human could do.

The boats ripped through the waters at terrific speed and in a few seconds there loomed before them the giant metal wall of the great dome, going down into the depths here. Norman glimpsed vaguely that the whole colossal dome rested on a vast pedestal-like mountain of rock that rose from the sea’s floor almost to the surface. Then a great round opening in the wall; the boats flashed into it and were hurtling along a water-filled tunnel. Norman felt his lungs near bursting--when the tunnel turned sharply upward and the boats whizzed up and abruptly out of the water-tunnel into air!

But it was not the open air again. They were beneath the gigantic dome! For as Norman and Hackett breathed deep, awe fell on their faces as they took in the scene. Far overhead stretched the dome’s colossally curving roof, and far out on all sides. It was lit beneath that roof by a clear light that the two would have sworn was sunlight. The dome was in effect the roof of a gigantic, illuminated building, and upon its floor there stretched a mighty city.

The city of the frog-men! Their boats were rising up over it and Norman and Hackett saw it clear. Square mile upon square mile of structures stretched beneath the dome, black buildings often of immense size, varying in shape, but all of square, rectangular proportions. Between them moved countless frog-hordes, swirling throngs in streets and squares, and over the roofs darted thick swarms of flying-boats. And at the city’s center, in a great, circular, clear space, lay a wide, round, green pool--the opening of the water-tunnel up through which they had come.

Norman pointed down toward it. “That’s your answer!” he cried. “The only entrance to this frog-city is from the sea, up through that water-tunnel!”

“Good God, an amphibian city!” Hackett was shaken, white-faced.

The two boats were driving quickly over the city, through the swarming craft. Norman glimpsed towering buildings that might have been palaces, temples, laboratories. They slowed and dipped toward one block-like building not far from the water-tunnel’s opening. Armed frog-guards were on its roof, and other boats rested there. The two came to rest and the two captives were jerked out, the guards seizing them.

Half-dragged and half-floating they were led toward an opening in the roof from which a stair led downward. They passed down thus into the building’s interior, lit by many windows. Norman glimpsed long halls ending in barred doors, guards here and there. Tube-lines ran along the walls and somewhere machines were throbbing dully. They came at last to a barred door whose guard opened it at the croaking order of the frog-men who held the two, and they were thrust inside, as the door clanged. They turned, and exclaimed in amazement. The room held fully a half-hundred men!

They were men such as the two fliers had never seen before, like humans except that their skins were a light green instead of the normal white and pink. They were dressed in dark short tunics, and kept talking to each other in a tongue quite unintelligible to Norman and Hackett. They came closer, flocking curiously around the two men, with a babel of voices quite meaningless to the two. Then one of the men uttered an exclamation, and all turned.

The barred door had swung open and a half-dozen frog-guards entered, followed by two frog-men carrying a square little mechanism from which tubing led back out through the door.

“Norman--these men--” Hackett was whispering rapidly. “If there are men in this world too, it may be that--”

“Quiet, Hackett--look at what they’re doing.”

The two frog-men had set their mechanism in place and then croaked out a brief word or order. Slowly, reluctantly, one of the green men moved toward them. Quickly they removed a metal disk fastened to his arm, exposing a small orifice like an unhealed wound. Onto this they fastened a suckerlike object from which a transparent tube led back through the mechanism. The machine hummed and at once a red stream pulsed through the tube and back through the mechanism. The man to whom it was attached was growing rapidly pale!

Norman, sick with horror, clutched his companion. “Hackett--these frog-men are sucking his blood from him!”

“Good God! And look--they’re doing it with another!”

“All of these men--kept prisoners to furnish them with blood. It must be the damned creatures’ food! And we here with the others--”

A common horror shook the two. It did not seem to affect the green men in the room, though, who advanced to the mechanism one by one with a reluctant air as of cows unwilling to be milked. Each was attached to the mechanism by the sucking disk on his arm, and out of each the blood poured through the tube. The metal disk was replaced on his arm then and he went back to the others. Norman saw that the frog-men took only from each an amount of blood that they could lose and yet live, since, though each came back pale and weak from the mechanism, they were able to walk.

“It must be their food--human blood!” Norman repeated. “They may have thousands on thousands of humans penned up like this, like so many herds of cows, and perhaps they live entirely on the life-blood they milk from them. Human cows--God!”

“Norman--look--they’re calling to us!”

The two stiffened. All the others in the room had taken their turn at the blood-sucking mechanism and now the frog-men croaked their order to the two fliers. They had forgotten their own predicament in the horror of the scene, but now it became real to them. They backed against the room’s wall, quivering, dangerous.

The frog-guards came forward to drag them to the machine. A webbed paw was outstretched but Hackett with a wild blow drove the frog-man back and downward. The frog-guards leaped, and Norman and Hackett struck them back with all the greater strength the lesser gravitation gave them. The room was in an uproar, the green men shouting hoarsely and seeming on the point of rushing to their aid.

But the menacing force-pistols of the other frog-guards held back the shouting men and in moments the two fliers were overpowered by sheer weight of frog-bodies. Norman felt himself dragged to the machine.

Pain needled his upper arm as an incision was made. He felt the sucking-disk attached; then the machine hummed, and a sickening nausea swept him as the blood drained from his body. Held tightly by the guards he went dizzy, weak, but at last felt the sucker removed and a metal disk fastened over the incision. He was jerked aside and Hackett, his face deathly white, was dragged into his place. In a moment some of the latter’s blood had been pumped from him also.

The machine was withdrawn, Norman and Hackett were released, and the frog-men, with their black force-pistols watchfully raised, withdrew, the door clanging. The room settled back to quietness, the green men stretching in lassitude on the metal bunks around it. The two fliers crouched down near the door, shuddering nausea and weakness still holding them.

Norman found that Hackett was laughing weakly. “To think that twenty-four hours ago I was in New York,” he half-laughed, half-sobbed. “On Earth--Earth--”

The other gripped his arm. “It’s horrible, Hackett, I know. But it isn’t instant death, and we’ve still a chance to escape. Hell, can damn frog-men keep us here? Where’s your nerve, man?”

A voice beside them made them turn in amazement. “You are men from Earth?” it asked, in queerly accented English. “From Earth?”

Astonishment held them as they saw who spoke. It was one of the green men in the room, who had settled down by their side. A tall figure with superb muscles and frank, clean countenance, his dark eyes afire with eagerness.

“English?” Norman exclaimed. “You know English--you understand me?”

The other showed his teeth in a smile. “I know, yes. I’m Sarja, and I learned to speak it from Fallas, in my city, before the Ralas caught me.”

“Fallas--” Norman repeated, puzzled; then suddenly he flamed. “By God, he means Fellows!”

“Fallas, yes,” said the other. “From the sky he fell into our city in a strange flying-boat that was smashed. He was hurt but we cared for him, and he taught me his speech, which I heard you talking now.”

“Then Fellows is in your city now?” asked Hackett eagerly. “Where is that?”

“Across this sea--back in the hills,” the other waved. “It is far from the sea but I was rash one day and came too near the water in my flying-boat. The Ralas were out raiding and they saw me, caught me, and brought me here. No escape now, until I die.”

“The Ralas--you mean these frog-men?” Norman asked.

Sarja nodded. “Of course. They are the tyrants and oppressors of this world. Our little world is but a tenth or less the size of your great Earth which it circles, but it has its lands and rivers, and this one great fresh-water sea into which the latter empty. In this sea long ago developed the Ralas, the great frog-men who acquired such intelligence and arts that they became lords of this world.

“Through the centuries, while on the land our races of green men have been struggling upward, the Ralas have oppressed them. Long ago the Ralas left all their other cities to build this one great amphibian city at the sea’s center. Entrance to it is only by the water-tunnel from without, and being frog-people entrance thus is easy for them since they can move for many minutes under water, though they drown like any other breathing animal if kept under too long. Humans dare not try to enter it thus by the water-tunnel, since, before they could find it and make their way up through it, they would have drowned.

“So the Ralas have ruled from this impregnable amphibian city. Its colossal metal dome is invulnerable to ordinary attack, and though solid and without openings it is always as light beneath the dome here as outside, since the Ralas’ scientists contrived light-condensers and conductors that catch light outside and bring it in to release inside. So when it is day outside the sunlight is as bright here, and when night comes the Earth-light shines here the same as without.

“From this city their raiding parties have gone out endlessly to swoop down on the cities of us green men. Since we learned to make flying-boats like theirs, with molecular-motors, and to make the guns like theirs that fire shells filled with annihilating force, we have resisted them stoutly but their raids have not ceased. And always they have brought their prisoners back in to this, their city.

“Tens of thousands of green men they have prisoned here like us, for the sole purpose of supplying them with blood. For the Ralas live on this blood alone, changing it chemically to fit their own bodies and then taking it into their bodies. It eliminates all necessity for food here for them. Every few days they drain blood from us, and since we are well fed and cared for to keep us good blood-producers, we will be here for a long time before we die.”

“But haven’t you made any attempt to get out of here--to escape?” Norman asked.

Sarja smiled. “Who could escape the city of the Ralas? In all recorded history it has never been done, for even if by some miracle you got a flying-boat, the opening of the water-tunnel that leads outward is guarded always.”

“Guards or no guards, we’re going to try it and not sit here to furnish blood for the Ralas,” Norman declared. “Are you willing to help, to try to get to Fellows and your city?”

The green man considered. “It is hopeless,” he said, “but as well to die beneath the force-shells of the Ralas as live out a lifetime here. Yes, I will help, though I cannot see how you expect to escape even from this room.”

“I think we can manage that,” Norman told him. “But first--not a word to these others. We can’t hope to escape with them all, and there is no knowing what one might not betray us to the frog-men.”

He went on then to outline to the other two the idea that had come to him. Both exclaimed at the simpleness of the idea, though Sarja remained somewhat doubtful. While Hackett slept, weak still from his loss of blood, Norman had the green man scratch on the metal floor as well as possible a crude map of the satellite’s surface, and found that the city, where Fellows was, seemed some hundreds of miles back from the sea.