After the first suspicions had worn off, the Earthmen felt that they had been singularly fortunate. To be captured by these intelligent beings had been about the most convenient thing that could happen to them. They might have found the human race entirely wiped out on the gloomy planet. Or they might have been struck by one of the still inconveniently numerous meteorites which would mean, at the very least, being marooned. Had they possessed the ability to look into the future they would not have rested quite so complacently in the hammocks assigned to them in the great patrol ship.

The big Jovian, they learned, was chief of the ship. He told them his name was Musters, and introduced his officers. They were an intelligent, efficient lot. From them the Earthmen learned something of the social organization of the human race as it survived on Jupiter.

"The race followed its natural evolution," intelligent and handsome young Lieutenant Reko explained to Sine as they leaned against a railing and gazed out of an unshuttered port at the somber splendors of Jupiter as it gradually swelled and covered the firmament.

"Like mated to like, and so the superior individuals became more superior, and the inferior ones more inferior. This resulted eventually in two races. Naturally we took steps to properly segregate the inferior race. Our efficiency experts have found ways to put them to work—to make them quite useful in fact. Of course we could not trust them with our weapons, our ships, our really important central power plants——"

What were these inferior—these so-called Mugs—what were they like? Reko arched aristocratic eyebrows. Why, they were often quite human in their appearance—though occupational diseases, and so forth——. Sine gained the impression that they were kept out of the way in order not to disturb the esthetic comfort of the superior race.

"There was a time when we had trouble with them," Lieutenant Reko said. "There were trouble makers among them. They attacked the homes of the First race, seized power control stations. Not fifty years ago there was an insurrection. But the Mugs lost. Thousands upon thousands of them were driven into the swamps and caves on the edge of the Tenebrian Sea. They were never seen again, although we searched for them with our heat rays. Perished, no doubt."

None were left now, Reko said, except those actually and fully occupied at certain labors for which they were found efficient. They were allowed to reproduce in sufficient numbers to fill the requirements—no more.

"What a rotten fate!" Sine exclaimed.

"They are quite a terrible people," Reko pointed out, closing a distasteful subject.

A few sleep periods later Musters called his terrestrial guests to his cabin.

"I have a pleasant surprise for you," he told them in his musical baritone. "Our planetary conference would wish for me to give you a most pleasant impression of Jupiter, so that interplanetary relations may be resumed under the best possible conditions. For that reason I am going to land you on a satellite that I'll wager will be a revelation to you. It is the goal and object of every one of our people. But it is costly and only a small portion of our population can be accommodated at a time. You may judge the kind of place it is by the name the public has given it: 'The Pleasure Bubble.' Come to the astrogator's cabin now; I'll show it to you."

They followed Musters to a compartment in the rounded bow of the great ship, stared out of a quartz port between opened shutters.

They saw Jupiter, immense, formidable, a mass of turbulent vapors, a depressingly drab scene. Suddenly Lents exclaimed, incredulous;

"Look! A satellite! There is no satellite this close to Jupiter! It's mathematically impossible!"

Musters laughed jovially. "It's there, isn't it? That's Jupiter's tenth satellite—The Bubble. It is less than 100,000 miles from the vapor envelope and has to travel so fast that its period is less than 8 hours. It was built by the First Race and set on its orbit so that our people would have a place where they could enjoy the sun, which is never seen from Jupiter's surface."

"It is a bubble!" Kass remarked, after an absorbed study of the satellite. It was racing just beneath them, at a dizzy speed, like a bubble blown before the wind. The ship followed the satellite, drawing closer, so that it grew in size and beauty.

Lents was mentally calculating the rupturing pressure exerted by the atmospheric pressure inside the crystalline ball. He stopped aghast at the thought of the tremendous strain.

"That crystalline material stands the strain easily," Musters assured them. "It will resist anything but a direct hit by a very large meteorite. As you can see now, the sphere, which is about a mile in diameter, is bi-sected by a plane surface, on which the city is built. In that little area you will see reproduced the choicest conditions of Earth." He turned earnest, hungry eyes on them:

"You don't know how lucky you people of Earth are!"

The ship was now coming quite close to the vast curve of the crystal, and they could see glimpses of beautiful structures in fairylike colorings, of small lakes like exquisite gems, of brilliant bursts of light that they conjectured served as substitutes for the sun while it was occulted by the enormous bulk of the planet.

Steadily the ship swept downward, to the level of the city, and the Earthmen became aware that the entire sphere was not transparent crystal. The part below the city level was a dull, ugly black.

"That's where the machinery is," Musters answered their questions, somewhat shortly, it seemed. "Hydrogen integrators there—to generate the power. Leakage of injurious rays down there—couldn't expect the First race to work there."

"Who does run the machinery?" Sine asked curiously.

"The labor Mugs, of course!" And Musters changed the subject.

The chief left them to their own devices as he superintended the lining up of the big ship's airlocks with the lock gasket of The Bubble. This effected, he bid his guests courteous farewell, assuring them that their ship would be conveyed to the Jovian capital city of Rubio, where they would be given every facility for repairing their damaged motor.

Sine was awakened by the talking of Kass and Lents as they sat at their breakfast in their unimaginably luxurious apartment. They were near the top of one of the fairylike towers they had glimpsed, and through the crystalline roof they could see the blackness of star-studded space. Far above was the glint of slanting sunlight on the outer covering of the sphere. This was the fourth morning on The Bubble, and the Earthmen were beginning to become vaguely restless. Their hosts had entertained them royally, but—

"I didn't see anything funny about the way they shoved that labor Mug out of the airlock," Lents was saying. "The poor devil! Stole a little of the juice they call ambrosia. The way that elegant over-civilized crowd laughed!"

"They lined up and watched the body floating alongside," Kass added somberly. "And that Mug was as human as you or I."

Their words recalled the scene vividly to Sine's mind. The broad, green field between two crescent lakes. The beetling-browed wretch, with eyes full of fear that darted from side to side, led to the center of the field by two splendidly armed warriors, there to be left alone in an agony of uncertainty.

He saw again the half-hundred clean-limbed athletes, sons of rich Jovian families. They were lined upon each side of the field. At the signal they dashed in. The frightened labor Mug tried to escape. As one team closed in he doubled, ran directly toward the others, saw his mistake too late. There was a brief savage scrimmage, and the unfortunate victim was stretched unconscious on the sward, while the victors and the vanquished in this curious game joined arms and made for the baths where exquisite nymphs peered coquettishly from behind delicately proportioned columns. Sine reaped uncomprehending and resentful stares when he declined to join them.

"Too rich for my blood," Sine told his companions at breakfast as they discussed their experiences. "Hope they take us to Rubio soon. We've done our job, and as for me, I'm not cut out for high Society."

After they had completed their breakfast a girl came hesitatingly into their chamber. Sine stared at her curiously. She had none of the enameled beauty of the women he had seen until then, but in her young face was a subdued comeliness that was attractive after the assertive pulchritude that was universal among the young women of the First Race. Unlike the shrewd display of their chiseled perfection, this girl's slender, rounded body was wrapped in a thin, gray garment that concealed as it draped. It was caught by a cord around her waist. Her feet, smaller and more fragile than the sturdy Jovian standard, were encased in neutral buskins. She stood submissively, waiting for them to speak.

"What does that girl want?" Kass murmured aside. "My stars, she can't be a labor Mug!"

"Come here, girl!" Lents rumbled kindly. "What can we do for you?"

The girl came forward hesitatingly. Her voice was soft, lacking the brassy assurance of other Jovian women;

"I was sent here, masters, to guide you through hell."

Immediately after this startling statement her face turned a brilliant red, then a deathly white. She half turned as if to flee, but, as if realizing the uselessness of flight, she faced them again, defiantly;

"I don't care what happens to me!" she declared desperately. "I've told the truth at least once. Jovians call this place The Pleasure Bubble, but they don't have to live in the black half. Now tell them what I have said."

"We will not tell anyone what you said, child," Lents rumbled comfortingly. "But tell us. You don't look like the Mugs we've seen so far—nor like the poor fellow we saw put through the airlock. They seemed—a different race. But you—why—on Earth we could hardly tell you from any other kid of your age."

A flash of spirit illuminated the girl's tragic, immature face.

"They call us a different race!" she exclaimed. "True—but not an inferior race! They are the inferior race, though the stronger. They depend on our knowledge, our labor, to live! My father told me so!"

Kass, who had been studying her silently, asked, "Your father?"

"Yes. The technic in charge of the machinery below. He was ordered to escort you around. But his scars from the rays make it hard for him to breathe today. He is in his bunk. So he sent me in his place."

Sine wondered if life under such unnatural and destructive conditions would some day reduce this graceful girl to a horrible parody of humanity. He asked;

"Do you work below?"

Her clear gray eyes fell on him.

"No. I was selected by the Committee to work in the Baths when I am sixteen. I am fifteen now."

"Holy twisted nebulae!" Sine swore under his breath. "The kid doesn't know what her work in the Baths is going to be! So the Committee selected her for the Baths!" He felt suddenly a violent dislike for the very rich Jovians, a feeling of fraternity with the Mugs.

"We will be very glad to have you guide us," he said formally. "What is your name?"

"Proserpina. My father said it is fitting for one who lives where we do."

Strange anachronism! That name from the mythology of Earth's youth. Like that goddess of the underworld from misty antiquity, she led them down, down, until it seemed they must be near the bottom of the black hemisphere. It was a world of dim distances, of shadows, of pipes and girders, or grisly abysses from which came mysterious sounds; of locked chambers in which ghastly fires flared.

Now and then they met the inhabitants of the place; misshapen Robolds going about unknown tasks. They stumbled suddenly out of unnoticed passages, carrying burdens, grotesque, apelike, weary. Most of them were hideously deformed.

Several times, when their journey led them into a certain part of the hemisphere where they felt strange tingling of their nerves, the girl led them away.

"We must not go there," she told them. "The integrators are there. There my father received the scars of his chest that keep him from breathing. Most of those who are blind worked there."

The Earthmen had already heard hints of the atomic integrators from which the Jovians obtained endless power. They had no desire to get too near those searing by-products of power.

"Do you mean to say," Lents asked, puffing a little from their exertions, "that people down here live here all their lives?"

"I will show you our home," Proserpina said simply.

They came to it presently. A niche, a metal-laced nook, deep in the hull. Gigantic girders formed one side of it. On the other side enormous air conduits. It was clean, bare, not as depressing as they had expected. It was more like a gallery, long and narrow, sparsely furnished.

Something rolled out of a bunk at the farther end. Something like a great spider. A man, stooped over, his once powerful body doubled, so that his knuckles almost dragged on the floor-plates. He came toward them, fierce gray eyes looking out at them under bushy brows. So formidable that Sine's muscles tensed.

"Are these the visitors, Proserpina?" His voice was husky, as though his constricted chest with difficulty performed its function. He looked at them intensely.

"They tell me you are from Earth. Are you with us or against us?"

"Father, be careful!" She put her hand over his mouth, to be shaken off impatiently. But the girl's warning had taken effect. The man—it was impossible to tell if he were old or young—looked at them broodingly.

"My mother died here," Proserpina said. "And I am afraid he will. His mind is not as clear—"

Lents, distressed to the bottom of his generous soul, helped the victim of the Jovian pleasure moon back to his bunk. "This girl," he muttered to Kass, "can't we get her out of here?"

He had not meant for her to hear, but her quick ears caught his words, and a ray of hope illuminated her features. She was standing beside Sine, and her thin fingers gripped his hard bronzed arm;

"Oh, could you take me away? I will be your slave!"

Sine gently disengaged her fingers. He was strangely embarrassed.

"I'd like to. But I'm a bachelor man. No place for you, you know."

She did not persist. No doubt she realized that she could not leave that gaunt parody of a man who was her father.

When they bid farewell to Proserpina they were steeped in profound depression. Alone in their room, they talked over what they had seen, but they could think of no way to save Proserpina from her fate. They were still discussing their visit when the manager of this satellite of delights called on them and informed them that Governor Nikkia of Jupiter awaited them in the capital city, Rubio. A space ferry was even then clamped to the locks to take them to the mother planet.