The Ancient Mariner hung high in the air, poised twenty-five miles above the surface of the little lake. Wade, as chemist, tested the air while the others readied the distillation and air condensation apparatus. By the time they had finished, Wade was ready with his report.

"Air pressure about 20 psi at the surface; temperature around ninety-five Fahrenheit. Composition: eighteen percent oxygen, seventy-five percent nitrogen, four-tenths of one percent carbon dioxide, residue—inert gasses. That's not including water vapor, of which there is a fair amount.

"I put a canary into the air, and the bird liked it, so I imagine it's quite safe except for bacteria, perhaps. Naturally, at this altitude the air is germ-free."

"Good," said Morey, "then we can take our swim and work without worrying about spacesuits."

"Just a minute!" Fuller objected. "What about those germs Wade mentioned? If you think I'm going out in my shorts where some flock of bacteria can get at my tender anatomy, you've got another think coming!"

"I wouldn't worry about it," Wade said. "The chances of organisms developing along the same evolutionary line is quite slim. We may find the inhabitants of the same shape as those of another world, because the human body is fairly well constructed anatomically. The head is in a place where it will be able to see over a wide area and it's in a safe place. The hand is very useful and can be improved upon but little. True, the Venerians have a second thumb, but the principle is the same.

"But chemically, the bodies are probably very different. The people of Venus are widely different chemically; the bacteria that can make a Venerian deathly ill is killed the instant it enters our body, or else it starves to death because it can't find the kind of chemical food it needs to live. And the same thing happens when a Venerian is attacked by an Earthly microorganism.

"Even on Earth, evolution has produced such widely varying types of life that an organism that can feed on one is totally incapable of feeding on another. You, for instance, couldn't catch tobacco mosaic virus, and the tobacco plant can't catch the measles virus.

"You couldn't expect a microorganism to evolve here that was capable of feeding on Earth-type tissues; they would have starved to death long ago."

"What about bigger animals?" Fuller asked cautiously.

"That's different. You would probably be indigestible to an alien carnivore, but he'd probably kill you first to find out. If he ate you, it might kill him in the end, but that would be small consolation. That's why we're going to go out armed."

Arcot dropped the ship swiftly until they were hovering a bare hundred feet over the waters of the lake. There was a little stream winding its way down the mountainside, and another which led the clear overflow away.

"I doubt if there's anything of great size in that lake," Arcot said slowly and thoughtfully. "Still, even small fish might be deadly. Let's play safe and remove all forms of life, bacterial and otherwise. A little touch of the molecular motion ray, greatly diffused, will do the trick."

Since the molecular ray directed the motion of the molecules of matter, it prevented chemical reactions from taking place, even when greatly diffused; all the molecules tend to go in the same direction to such an extent that the delicate balance of chemical reactions that is life is upset. It is too delicate a thing to stand any power that upsets the reactions so violently. All things are killed instantly.

As the light haze of the ionized air below them glowed out in a huge cone, the water of the lake heaved and seemed to move in its depths, but there was no great movement of the waters; they lost only a fraction of their weight. But every living thing in that lake died instantly.

Arcot turned the ship, and the shining hull glided softly over to one side of the lake where a little sandy beach invited them. There seemed no indication of intelligent life about.

Each of them took a load of the supplies they had brought, and carried them out under the shade of an immense pine-like tree—a gigantic column of wood that stretched far into the sky to lose its green leaves in a waving sea of foliage. The mottled sunlight of the bright star above them made them feel very much at home. Its color, intensity, and warmth were all exactly the same as on Earth.

Each of the men wore his power suit to aid in carrying the things they had brought, for the gravity here was a bit higher than that of Earth. The difference in air pressure was so little as to be scarcely noticeable; they even adjusted the interior of the ship to it.

They had every intention of staying here for awhile. It was pleasant to lie in the warm sun once more; so pleasant that it became difficult to remember that they were countless trillions of long miles from their own home planet. It was hard to realize that the warm, blazing star above them was not Old Sol.

Arcot was carrying a load of food in a box. He had neutralized his weight until, load and all, he weighed about a hundred pounds. This was necessary in order to permit him to drag a length of hose behind him toward the water, so it could be used as an intake for the pumps.

Morey, meanwhile, was having trouble. He had been carrying a load of assorted things to use—a few pneumatic pillows, a heavy iron pot for boiling the water, and a number of other things.

He reached his destination, having floated the hundred or so feet from the ship by using his power suit. He forgot, momentarily, and dropped his load. Immediately, he too began to "drop"—upward! He had a buoyancy of around three hundred pounds, and a weight of only two fifty. In dropping the load, the sudden release had caused the power unit to jerk him upward, and somehow the controlling knob on the power pack was torn loose.

Morey shot up into the air, showing a fair rate of progress toward his late abode—space! And he had no way to stop himself. His hand power unit was far too weak to overcome the pull of his power-pack, and he was rising faster and faster!

He realized that his friends could catch him, and laughingly called down: "Arcot! Help! I'm being kidnapped by my power suit! To the rescue!"

Arcot looked up quickly at Morey's call and realized immediately that his power control had come off. He knew there was twenty miles or so of breathable air above, and long before Morey rose that far, he could catch him in the Ancient Mariner, if necessary.

He turned on his own power suit, using a lift of a hundred pounds, which gave him double Morey's acceleration. Quickly he gathered speed that shot him up toward his helpless friend, and a moment later, he had caught up with him and passed him. Then he shut off his power and drifted to a halt before he began to drop again. As Morey rose toward him, Arcot adjusted the power in his own suit to match Morey's velocity.

Arcot grabbed Morey's leg and turned his power down until he had a weight of fifty pounds. Soon they were both falling again, and when their rate of fall amounted to approximately twenty miles per hour, Arcot cut their weight to zero and they continued down through their momentum. Just short of the ground, he leaped free of Morey, who, carried on by momentum, touched the ground a moment later. Wade at once jumped in and held him down.

"Now, now! Calm yourself," said Wade solicitously. "Don't go up in the air like that over the least little thing."

"I won't, if you'll get busy and take this damned thing off—or fasten some lead to my feet!" replied Morey, starting to unstrap the mechanism.

"You'd better hold your horses there," said Arcot. "If you take that off now, we sure will need the Ancient Mariner to catch up with it. It will produce an acceleration that no man could ever stand—something on the order of five thousand gravities, if the tubes could stand it. And since that one is equipped with the invisibility apparatus, you'd be out one good invisibility suit. Restrain yourself, boy, and I'll go get a new knob control.

"Wade, get the boy a rock to hold him down. Better tie it around his neck so he won't forget it and fly off into space again. It's a nuisance locating so small an object in space and I promised his father I'd bring the body back if there was anything left of it." He released Morey as Wade handed him a large stone.

A few minutes later, he returned with a new adjustment dial and repaired Morey's apparatus. The strain was released when he turned it, and Morey parted with the rock with relief.

Morey grunted in relief, and looked at the offending pack.

"You know, that being stuck with a sky-bound gadget that you can't turn off is the nastiest combination of feeling stupid, helpless, comical, silly and scared I've hit yet. It now—somewhat late—occurs to me that this is powered with a standard power coil, straight off the production line, and that it has a standard overload cut-out for protection of associated equipment. I want to install an emergency cutoff switch, in case a knob, or something else, goes sour. But I want to have the emergency overload where I can decide whether or not an emergency overload is to be accepted. I'd feel a sight more than silly if that overload relay popped while I was a couple thousand feet up.

"Trouble with all this new stuff of ours is that we simply haven't had time to find out all the 'I never thought of that' things that can go wrong. If the grid resistor on that oscillator went out, for instance, what would it do?"Arcot cocked an eye at the power pack, visualizing the circuits. "Full blast, straight up, and no control. But modern printed resistors don't fail."

"That's what it says in all the books." Wade nodded wisely. "And you should see the stock of replacement units every electronics shop stocks for purposes of replacing infallible units, too. You've got a point, my friend."

"I can see four ways we can change these things to fail-safe operation, if we add Morey's emergency cut-off switch. If it did go on-full then, you could use intermittent operation and get down," Arcot acknowledged.

"Anybody know what silly fail-unsafe tricks we overlooked in the Ancient Mariner?" Fuller asked.

"That," said Wade with a grimace, "is a silly question. The 'I didn't think of that' type of failure occurs because I didn't think of that, and the reason I didn't think of it is because it never occurred to me. If we'd been able to think of 'em, we would have. We'll probably get stuck with a few more yet, before we get back. But at least we can clean up a few bugs in these things now."

"Forget it for now, Wade, and get that chow on," suggested Fuller. He was lying on his back, clad only in a pair of short trunks, completely relaxed and enjoying life. "We can do that when it's dark here."

"Fuller has the right idea," said Morey, looking at Fuller with a judicious eye. "I think I'll follow his example."

"Which makes three in favor and one on the way," said Arcot, as he came out of the ship and sank down on the soft sand of the beach.

They lay around for a while after lunch, and then decided to swim in the cool waters of the lake. One of them was to stand guard while the others went in swimming. Standing guard consisted of lying on his back on the soft sand, and staring up at the delightful contrast of lush green foliage and deep blue sky.

It was several hours before they gathered up their things and returned to the ship. They felt more rested than they had before their exercise. They had not been tired before, merely restless, and the physical exercise had made them far more comfortable.

They gathered again in the control room. All the apparatus had been taken in; the tanks were filled, and the compressed oxygen replenished. They closed the airlock and were ready to start again.

As they lifted into the air, Arcot looked at the lake that was shrinking below them. "Nice place for a picnic; we'll have to remember that place. It isn't more than twenty million light years from home."

"Yes," agreed Morey, "it is handy. But suppose we find out where home is first; let's go find the local inhabitants."

"Excellent idea. Which way do we go to look?" Wade asked.

"This lake must have an outlet to the sea," Morey answered. "I suggest we follow it. Most rivers of any size have a port near the mouth, and a port usually means a city."

"Let's go," said Arcot, swinging the shining ship about and heading smoothly down along the line of the little stream that had its beginning at the lake. They moved on across the mountains and over the green foothills until they came to a broad, rolling plain.

"I wonder if this planet is inhabited," Arcot mused. "None of this land seems to be cultivated."

Morey had been scanning the horizon with a pair of powerful binoculars. "No, the land isn't cultivated, but take a look over there—see that range of little hills over to the right? Take a look." He handed the binoculars to Arcot.

Arcot looked long and quietly. At last he lowered the binoculars and handed them to Wade, who sat next to him.

"It looks like the ruins of a city," Arcot said. "Not the ruins that a storm would make, but the ruins that high explosives would make. I'd say there had been a war and the people who once lived here had been driven off."

"So would I," rejoined Morey. "I wonder if we could find the conquerors?"

"Maybe—unless it was mutual annihilation!"

They rose a bit higher and raised their speed to a thousand miles an hour. On and on they flew, high above the gently rolling plain, mile after mile. The little brooklet became a great river, and the river kept growing more and more. Ahead of them was a range of hills, and they wondered how the river could thread its way among them. They found that it went through a broad pass that twisted tortuously between high mountains.

A few miles farther on, they came to a great natural basin in the pass, a wide, level bowl. And in almost the exact center, they saw a looming mass of buildings—a great city!

"Look!" cried Morey. "I told you it was inhabited!"

Arcot winced. "Yes, but if you shout in my ear like that again, you'll have to write things out for me for ever after." He was just as excited as Morey, nevertheless.

The great mass of the city was shaped like a titanic cone that stood half mile high and was fully a mile and a half in radius. But the remarkable thing about it was the perfect uniformity with which the buildings and every structure seemed to conform to this plan. It seemed as though an invisible, but very tangible line had been drawn in the air.

It was as though a sign had been posted: "Here there shall be buildings. Beyond this line, no structure shall extend, nor any vehicle go!"

The air directly above the city was practically packed with slim, long, needle-like ships of every size—from tiny private ships less than fifteen feet long to giant freighters of six hundred feet and longer. And every one of them conformed to the rule perfectly!

Only around the base of the city there seemed to be a slight deviation. Where the invisible cone should have touched the ground, there was a series of low buildings made of some dark metal, and all about them the ground appeared scarred and churned.

"They certainly seem to have some kind of ray screen over that city," Morey commented. "Just look at that perfect cone effect and those low buildings are undoubtedly the projectors."

Arcot had brought the ship to a halt as he came through the pass in the mountain. The shining hull was in the cleft of the gorge, and was, no doubt, quite hard to see from the city.

Suddenly, a vagrant ray of the brilliant sun reached down through a break in the overcast of clouds and touched the shining hull of the Ancient Mariner with a finger of gold. Instantly, the ship shone like the polished mirror of a heliograph.

Almost immediately, a low sound came from the distant city. It was a pulsing drone that came through the microphone in a weird cadence; a low, beating drone, like some wild music. Louder and stronger it grew, rising in pitch slowly, then it suddenly ended in a burst of rising sound—a terrific whoop of alarm.

As if by magic, every ship in the air above the city shot downward, dropping suddenly out of sight. In seconds, the air was cleared.

"It seems they've spotted us," said Arcot in a voice he tried to make nonchalant.

A fleet of great, long ships was suddenly rising from the neighborhood of the central building, the tallest of the group. They went in a compact wedge formation and shot swiftly down along the wall of the invisible cone until they were directly over the low building nearest the Ancient Mariner. There was a sudden shimmer in the air. In an instant, the ships were through and heading toward the Ancient Mariner at a tremendous rate.

They shot forward with an acceleration that was astonishing to the men in the spaceship. In perfect formation, they darted toward the lone, shining ship from far-off Earth!