He looked at the expression on Bigman's face and said, "You'll get the idea as you go along. It becomes second nature after a while."

He stepped into the corridor and didn't drop an inch. It was as though he were standing on an invisible platform.

He said earnestly, "Have you set the dial at zero?''

Bigman did so, and instantly all sensation of gravity vanished. He stepped into the corridor.

Now the lieutenant's hand on the central knob of his own controls turned it sharply, and he sank, gathering speed. Lucky followed him, and Bigman, who would sooner have fallen the length of the corridor under double gravity and been smashed to pulp than fail to do anything Lucky did, took a deep breath and let himself fall.

"Turn back to zero," called the lieutenant, "and you'll be moving at constant velocity. Get the feel of it"

Periodically they approached and passed through luminous green letters that glowed keep to this side, Once there was the flash of a man passing (falling, really) in the other direction. He was moving much more rapidly than they were.

"Are there ever any collisions, Lieutenant?" asked Lucky.

"Not really," said the lieutenant. "The experienced dropper watches for people who might be overtaking him or whom he might be overtaking, and it's easy enough to slow down or speed up. Of course the boys will bump on purpose sometimes. It's a kind of rowdy fun that ends with a broken collarbone sometimes." He looked quickly at Lucky. "Our boys play rough."

Lucky said, "I understand. The commander warned me."

Bigman, who had been staring downward through the well-lit tunnel into which he was sinking, cried in sudden exhilaration, "Hey, Lucky, this is fun when you get used to it," and turned his controls into the positive region.

He sank faster, his head moving down to a level with Lucky's feet, then farther down at an increasing rate.

Lieutenant Nevsky cried out in instant alarm, "Stop that, you fool. Turn back into the negatives!"

Lucky called out an imperious, "Bigman, slow down!"

They caught up to him, the lieutenant angrily exclaiming. "Don't ever do that! There are all sort of barriers and partitions along these corridors, and if you don't know your way, you'll be slamming into one just when you think you're safe."

"Here, Bigman," said Lucky. "Hold the V-frog. That will give you some responsibility and make you behave, perhaps,"

"Aw, Lucky," said Bigman, abashed. "I was just kicking my heels a bit. Sands of Mars, Lucky…"

"All right," said Lucky. "No harm done," and Bigman brightened at once.

Bigman looked down again. Falling at a constant rate was not quite the same as free fall in space. In space, nothing seemed to move. A space ship might be traveling at a velocity of hundreds of thousands of miles an hour and there would still be the sensation of motion-lessness all about. The distant stars never moved.

Here, though, the sense of motion was all about. The lights and openings and various attachments that lined the corridor walls flashed past.

In space, one expected that there would be no "up" and "down," but here there was none either and it seemed wrong. As long as he looked "down" past his feet, it seemed "down" and that was all right. When he looked "up," however, there would be a quick sensation that "up" was really "down," that he was standing head downward falling "up." He looked toward his feet again quickly to get rid of the sensation.

The lieutenant said, "Don't bend too far forward, Bigman. The Agrav works to keep you lined up in the direction of fall, but if you bend over too much, you'll start tumbling."

Bigman straightened.

The lieutenant said, "There's nothing fatal about tumbling. Anyone who's used to Agrav can straighten himself out again. Beginners would find it troublesome, however. We'll decelerate now. Move the dial into the negatives and keep it there. About minus five."

He was slowing as he spoke, moving above them. His feet dangled at Bigman's eye level.

Bigman moved the dial, trying desperately to line himself up with the lieutenant. And as he slowed, "up" and "down" became definite, and in the wrong way. He was standing on his head.

He said, "Hey, the blood's rushing to my head."

The lieutenant said sharply, "There are footholds along the sides of the corridor. Hook one with the toe of your foot as you reach it and let go quickly."

He did so as he said this. His head swung outward, and head and feet reversed position. He continued swinging and stopped himself with a quick hand tap against the wall.

Lucky followed suit, and Bigman, flailing widely with his short legs, managed to catch one of the footholds at last. He whirled sharply and caught the wall with his elbow just a trifle too hard for comfort but managed to line up properly.

At least he was head-up again. He wasn't falling any more, but rising, as though he had been shot out of a cannon and rising against gravity more and more slowly; but at least he was head-up.

When they were moving at a slow crawl, Bigman, looking uneasily toward his feet, thought: We're going to be falling again. And suddenly the corridor looked like an endlessly deep well and his stomach tightened.

But the lieutenant said, "Adjust to zero," and at once they stopped slowing down. They just moved upward, as though in a smooth, slow elevator, until they reached a cross-level at which the lieutenant, seizing a foothold with one toe, brought himself to a feathery stop.

"Engineers' Quarters, gentlemen," he said.

"And," added Lucky Starr gently, "a reception committee."

For men were waiting for them in the corridor now, fifty of them at least.

Lucky said, "You said they liked to play rough, Lieutenant, and maybe they want to play now."

He stepped firmly out into the corridor. Bigman, nostrils flaring with excitement and grateful to be on the firm pseudo-grav of a solid floor, clutched the V-frog's cage tightly and was at Lucky's heels, facing the waiting men of Jupiter Nine.

Lieutenant Nevsky tried to make his voice crackle with authority as he placed his hand on the butt of his blaster. "What are you men doing here?"

There was a small murmur from the men, but by and large they remained quiet. Eyes turned to the one of them who stood in front, as though they were waiting for him to speak.

The leader of the men was smiling, and his face was crinkled into an expression of apparent good will. His straight hair, parted in the middle, had a light-orange tint to it. His cheekbones were broad and he chewed gum. His clothing was of synthetic fiber, as was true of that of the others, but unlike the others', his shirt and trousers were ornamented with brass buttons that were large and bulky. Four on his shirt front, one each on the two shirt pockets, and four down the side of each pants leg: fourteen altogether. They seemed to serve no purpose; to be only for show.

"All right, Summers," said the lieutenant, turning to this man, "what are the men doing here?"

Summers spoke now in a soft, wheedling voice.

"Well, now, Lieutenant, we thought it would be nice to meet the new man. He'll be seeing a lot of us. He'll be asking questions. Why shouldn't we meet him now?"

He looked at Lucky Starr as he spoke, and for a moment there was a touch of ice in that glance that swallowed up all the show of softness.

The lieutenant said, "You men should be at work."

"Have a heart, Lieutenant," said Summers, chewing even more slowly and leisurely. "We've been working. Now we want to say hello."

The lieutenant was obviously uncertain as to his next move. He looked doubtfully at Lucky.

Lucky said, "Which rooms are to be ours, Lieutenant?"