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 s.p.a.ce 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 alt.i.tudes 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 s.p.a.ce. 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 e.j.a.c.u.l.a.t.i.o.n.

"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 s.p.a.ce. 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.

CHAPTER VII

_Invisible Globe_

The buzzer of their radiophone was sounding, but so intent were they on this phenomenon they were facing, they paid it no heed. Their eyes were alight, their lips in firm straight lines of resolve, as they dived down upon the invisible obstruction--whatever it was--from whose surface the telltale updraft came.

It was Eyer who made the suggestion:

"Let's measure it to see what its plane extent is."

"How?" asked Jeter.

"Measure it by following the wind disturbance. We travel in one direction until we lose it. There is one extremity. In a few minutes we can discover exactly how big the thing is. What do you think it is?"

Jeter shook his head. There was no way of telling.

Jeter nodded agreement to Eyer. Then he spoke into the radiophone, telling Hadley what they had found, to which he could give no name.

"The world awaits in fear and trembling what you will have to report, Jeter," said Hadley. "What if you become unable to report, as Kress did?"

"Don't worry. We will or we won't. If we succeed we'll be back. If we fail, send up the other.... No, perhaps you hadn't better send up the new planes. But I think Eyer and I have a chance to discover the nature of this strange--whatever-it-is. If you can't contact us, delay twenty-four hours before doing anything. I--well, I scarcely know what to tell you to do. We'll just be shooting in the dark until we know what we're in for. You'll have to contain yourself in patience. What did you want with me?"

"Only to tell you of another strange news dispatch. It gives no details.

It merely tells of strange activity around Lake Baikal, beyond the Gobi Desert. Queer noises at night, mysterious cordons of Eurasians to keep all investigators back, strange losses of livestock, foodstuffs...."

Jeter severed connection. There was little need to listen further to something which he couldn't explain yet, in any case.

Eyer, at the controls, banked the plane at right angles and flew on. In shortly less than a minute he banked again.

In five minutes he turned to Jeter with a queer expression on his face.

"Well," he said, "what's to do about it? What is it? It seems to be some solid substance approximately a quarter mile square. But it can't be true! A solid substance just hanging in the air at ninety thousand feet!

It's beyond all imagining!"

"What man can imagine, man can do," replied Jeter. "A great newspaper editor said that, and we're going to discover now just how true it is."

"What's our next move?"

For a long time the partners, stared into each other's eyes. Each knew exactly what the other thought, exactly what he would propose as a course of action. Jeter heaved a sigh and nodded his head.

"We're as much in the power of the enemy here as we would be there, or anywhere else. We can't discover anything from here. Set the wheels down!"

"We can't tell anything about the condition of the surface of that stuff. We may crack up."

Jeter had to grin.

"Sounds strange, cracking up at ninety thousand feet, doesn't it? Well, hoist your helicopter vanes and drift down as straight as you can--but be sure and keep your motor idling."

Again they exchanged long looks.

"O.K.," said Eyer, as quietly as he would have answered the same order at Roosevelt Field. "Here we go!"

He pressed a b.u.t.ton and the helicopters, set into the surface of the single st.u.r.dy wing, snapped up their shafts and began to spin, effectually slowing the forward motion of the plane. Eyer fish-tailed her with his rudder to help cut down speed.

"We can't see the surface of the thing at all, Lucian," said Eyer. "I'll simply have to feel for it."

"Well, you've done that before, too. We can manage all right."

Down they dropped. The updraft was now a cushion directly under them.

And then their wheels struck something solid. The plane moved forward a few feet--with a strange sickening motion. It was as though the surface of this substance were globular. First one wheel rose, then dipped as the other rose. The plane came to rest on fairly even keel, and the partners, while the motor idled, stared at each other.