in the old Earth gesture of friendliness. His appearance had all the characteristics of his companions, but in a more striking degree. He was taller than they, more than five feet, and his broad shoulders had the confident bearing of accustomed command. He spoke, in a pleasant, vibrant baritone:

"Welcome, men of Earth. Sorry for our little misunderstanding."

Sine gripped his hand, returned the muscular grip.

"It took us a little while to know what you were. And I may add that I'm pleasantly surprised that we can still understand each other."

The Jovian shrugged his shoulder:

"Canned speech. No chance for a language to evolve when it's mechanically recorded. But come up to my cabin. It's chilly here, and your manner of dress——"

"That has changed!" Sine smiled. "Lents and Kass, will you go ahead?"

CHAPTER II

The Pleasure Bubble

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!"