Now the partner-scientists concentrated on the tremendous task of climbing higher than man had ever flown before. Nobody knew how high Kress had gone, for the only information which had come back had been the corpse of the sky pioneer. Jeter and Eyer hoped to land, too, but to be able to tell others, when they did, what had happened to them.

Somehow, away up here, the affairs of the Earth seemed trivial, unreal. What was the raising of an entire skyscraper—in reality so small that from this height it was difficult to pick out the biggest one through the telescope? What mattered a bridge across the Hudson that was really less than the footprint of an ant at this height?

Still, looking at each other, they were able to attain the old perspectives. Down there people like Jeter and Eyer were dying because of something that struck at them from somewhere up here in the blue darkness.

Their faces set grimly. The plane kept up its constant spiraling. Jeter and Eyer flew the ship in relays. Occasionally they secured the controls and allowed the plane to fly on, untended.

"But maybe we'd better not do too much of that," said Jeter dubiously. "I'm sure we are being observed, every foot of altitude we make. I don't care to run into something up here that will wreck us. Right now, Eyer, if we happened to be outside this sealed cabin instead of inside it, we'd die in less time than it takes to tell about it."

All known records for altitude—the only unknown one being Kress'—had now been broken by Jeter and Eyer. They informed Hadley of this fact.

"A week ago you'd have had headlines," came back Hadley. "To-day nobody cares, except that the world looks to you for information about this horror. The enemy is systematically destroying every building in Manhattan which dates back over eight years. Fortunately, save for the occasional die-hard who never believes anything, there are few deaths at the moment. But we're all waiting, holding our breaths, wondering what the next five minutes will bring forth. Is there any news there?"

How strange it seemed—as the altimeter said sixty-one thousand feet—to hear that voice out of the void. For under the plane there was no world at all, save through the telescope. Perhaps when morning came they would be able to see a little. Picard had reported the world to look flat from a little over fifty thousand-feet.

"No news, Hadley," said Jeter. "Except, that our plane behaves perfectly and we are at sixty-one thousand feet. Were it not for our turn and bank indicators, our altimeter and air speed instruments, and our navigational instruments, it would be impossible to tell—by looking at least, though we could tell by our shifting weight—whether we were upside down or right side up, on one wing or on an even keel. It's eery. We wouldn't be able to tell whether we were moving were it not for our air speed indicator. There are no clouds. The motor hum seems to be the only thing here—except ourselves of course—to remind us that we really belong down there with you."

The connection was broken again as Jeter ceased speaking. Things seemed to be marking time on the ground, save for the strange demolitions of the unseen and apparently unknowable enemy. Would they ever really encounter him, or it?

When the sun came out of the east they leveled off at ninety thousand feet. By their reckoning they had scarcely moved in any direction from the spot where they had taken off. Jeter was satisfied that they were almost directly above Mineola. But the world had vanished. The plane rode easily on. Now and again it dipped one wing or the other—and even the veteran aviators felt a thrill of uneasiness. From somewhere up here in this immensity, Franz Kress had dropped to his death. Of course, if it had happened at this height he hadn't lived to suffer.

Or had he? What had been done to him by the—the denizens of the stratosphere?

Jeter sat down beside Eyer. It seemed strange to eat breakfast here, but the sandwiches and hot coffee in a thermos bottle were extremely welcome. They ate in silence, their thoughts busy. When they had made an end, Jeter squared his shoulders. Eyer grinned.

"Well, Lucian," he said, "are we in enemy territory by your calculations? And if so how do you arrive at your conclusions?"

"I'm still guessing, Tema," said Jeter, "but I've a feeling I'm not guessing badly, and.... Yes, we're somewhere within striking distance of the enemy, whatever the enemy is."

"What's the next move?

"We'll systematically cover the sky over an area which blankets New York, Long Island, Jersey City and surrounding territory for a distance of twenty miles. If we're above the enemy, perhaps we can look down upon him. We know he can't be seen from below, perhaps not even from above. If we are below him we'll try to fly into that column of his. What they'll do to us I.... You're not afraid to find out, are you?"

Eyer grinned. Jeter grinned back at him.

"What they'll do to us if we fly into them I'm sure I don't know. I don't think they'll kill our motor. If whoever or whatever controls the light column decides to us prisoners.... Well, we'll hope to have better luck combating them than Kress had."

And so begin that hours-long vigil of quartering the stratosphere over the unmarked area which Jeter had set as a limit. Now and again Hadley spoke to Jeter. Yes, the demolitions were still continuing in Manhattan. Could all telescopes on the ground pick out their space ship? Yes, said Hadley, and a young scientist in New Jersey was constantly watching them. Were they, since sunrise, ever out of his sight? Only when clouds at comparatively low altitudes intervened. However, the sky was unusually clear and it was hoped to keep their plane in sight during the entire day.

"Hadley," Jeter almost whispered, "I'm satisfied we're above the area of force, else we'd have flown into the anti-gravitation field. Get in touch with that Jersey chap by direct personal wire or radiophone if he is equipped with it. See that his watch is set with yours, which is synchronised with ours. Got that?"

"Yes."

"When you've done that give him these instructions: He is never to take his eyes of us for more than a split second at a time—unless someone else takes his place. I doubt if, at this distance, this will work, but it may help us a little. If we become invisible for even the briefest of moments, he is to look at his watch and observe the exact time, even to split seconds. We shall try to follow a certain plan hereafter in quartering the stratosphere, and I shall mark our location on the navigational charts every minute until we hear from this chap, or until we decide nothing is to be accomplished by this trick. Understand?"

"You're hoping that the enemy, while invisible to all eyes, yet has substance...."

"Shut up!" snapped Jeter, but he was glad that Hadley had grasped the idea. It was a slim chance, but such as it was it was worth trying. If the plane were invisible for a time, then it would be proof of some opaque obstruction between the plane and the eye of the beholder on the surface of the Earth. Refraction had to be figured, perhaps. Oh, there were many arguments against it.

The fliers followed the very outer edge of the area above the world they had mapped out as their limit of exploration. This circuit completed, they banked inward, shortening their circuit by about a mile of space. A mile, seen at a distance of ninety thousand feet, would be little indeed.

It was almost midday when they had their first stroke of luck.

The buzzer sounded at the very moment Eyer uttered an ejaculation.

"The Jersey fellow says there is nothing between his lens and your plane to obstruct the view."

"O.K.," retorted Jeter. "At the moment your buzzer sounded our plane suddenly jumped upward. That means an upcurrent of air indicating an obstruction under us. It must however, be invisible."

He severed the connection. His brow was furrowed thoughtfully. He was remembering Sitsumi and his rumored discovery.

They circled back warily. The eyes of both were fixed downward, staring into space. Their jaws were firmly set. Their eyes were narrowed.

And then....

There was that uprush of air again! It appeared to rise from an angle of about sixty degrees. They got the wind against their nose and started a humming dive, feeling in the alien updraft for the obstruction which caused it.