"Just started," said Russ.

Greg straightened and glanced down the row of television machines. Some of them were dead, their switches closed, but on the screens of many of the others was the same effect as on this machine. Their operators were working frustratedly at the controls, trying to focus the image, bring it into sharp relief.

"Can't seem to get a thing, sir," said one of the men. "I was working on the fueling station out on Io, and the screen just went haywire."

"Mine seems to be all right," said another man. "I've had it on Sandebar for the last couple of hours and there's nothing wrong."

A swift check revealed one fact. The machines, when trained on the Jovian worlds, refused to function. Anywhere else in s.p.a.ce, however, they worked perfectly.

Russ stoked and lit his pipe, snapped off his machine and swung around in the operator's chair.

"Somebody's playing h.e.l.l with us out around Jupiter," he stated calmly.

"I've been expecting something like this," said Greg. "I have been afraid of this ever since Craven blanketed us out of the Interplanetary building."

"He really must have something this time," Russ agreed. "He's blanketing out the entire Jovian system. There's a s.p.a.ce field of low intensity surrounding all of Jupiter, enclosing all the moons. He keeps shifting the intensity so that, even though we can force our way through his field, the irregular variations make it impossible to line up anything.

It works, in principle, just as effectively as if we couldn't get through at all."

Greg whistled soundlessly through suddenly bared teeth.

"That takes power," he said, "and I'm afraid Craven has it. Power to burn."

"The collector field?" asked Russ.

Greg nodded. "A field that sucks in radiant energy. Free energy that he just reaches out and grabs. And it doesn't depend on the Sun alone. It probably makes use of every type of radiation in all of s.p.a.ce."

Russ slumped in his chair, smoking, his forehead wrinkled in thought.

"If that's what he's got," he finally declared, "he's going to be hard to crack. He can suck in any radiant vibration form, any s.p.a.ce vibration. He can shift them around, break them down and build them up.

He can discharge them, direct them. He's got a vibration plant that's the handiest little war machine that ever existed."

Greg suddenly wheeled and walked to a wall cabinet. From it he took a box and, opening it, lifted out a tiny mechanism.

He chuckled deep in his throat. "The mechanical shadow. The little machine that always tells us where Craven is--as long as he's wearing his gla.s.ses."

"He always wears them," said Russ crisply. "He's blind as a bat without them."

Greg set the machine down on the table. "When we find Craven, we'll find the contraption that's blanketing Jupiter and its moons."

Dials spun and needles quivered. Rapidly Russ jotted down the readings on a sheet of paper. At the calculator, he tapped keys, depressed the activator. The machine hummed and snarled and chuckled.

Russ glanced at the result imprinted on the paper roll.

"Craven is out near Jupiter," he announced. "About 75,000 miles distant from its surface, in a plane normal to the Sun's rays."

"A s.p.a.ceship," suggested Greg.

Russ nodded. "That's the only answer."

The two men looked at one another.

"That's something we can get hold of," said Greg.

He walked to the ship controls and lowered himself into the pilot's chair. A hand came out and hauled back a lever.

The _Invincible_ moved.

From the engine rooms came the whine of the gigantic power plant as it built up and maintained the gravity concentration center suddenly created in front of the ship.

Russ, standing beside Greg at the control panel, looked out into s.p.a.ce and marveled. They were flashing through s.p.a.ce, their speed building up at a breath-taking rate, yet they had no real propulsion power. The discovery of the gravity concentrator had outdated such a method of driving a s.p.a.ceship. Instead, they were falling, hurtling downward into the yawning maw of an artificial gravity field. And such a method made for speed, terrible speed.

Jupiter seemed to leap at them. It became a great crimson and yellow ball that filled almost half the vision plate.

The _Invincible's_ speed was slacking off, slower and slower, until it barely crawled in comparison to its former speed.

Slowly they circled Jupiter's great girth, staring out of the vision port for a sight of Craven's ship. They were nearing the position the little mechanical shadow had indicated.

"There it is," said Russ suddenly, almost breathlessly.

Far out in s.p.a.ce, tiny, almost like a dust mote against the great bulk of the monster planet, rode a tiny light. Slowly the _Invincible_ crawled inward. The mote of light became a gleaming silver ship, a mighty ship--one that was fully as large as the _Invincible_!

"That's it all right," said Greg. "They're lying behind a log out here raising h.e.l.l with our television apparatus. Maybe we better tickle them a little bit and see what they have."

Rising from the control board, he went to another control panel. Russ remained standing in front of the vision plate, staring down at the ship out in s.p.a.ce.

Behind him came a shrill howl from the power plant. The _Invincible_ staggered slightly. A beam of deep indigo lashed across s.p.a.ce, a finger suddenly jabbing at the other ship.

s.p.a.ce was suddenly colored, for thousands of miles, as the beam struck Craven's ship and seemed to explode in a blast of dazzling indigo light.

The ship reeled under the impact of the blow, reeled and weaved in s.p.a.ce as the beam struck it and delivered to it the mighty power of the screaming engines back in the engine room.

"What happened?" Greg screamed above the roar.

Russ shrugged his shoulders. "You jarred him a little. Pushed him through s.p.a.ce for several hundred miles. Made him know something had hit him, but it didn't seem to do any damage."

"That was pure cosmic I gave him! Five billion horsepower--and it just staggered him!"

"He's got a s.p.a.ce lens that absorbs the energy," said Russ. "The lens concentrates it and pours it into a receiving chamber, probably a huge photo-cell. n.o.body yet has burned out one of those things on a closed circuit."

Greg wrinkled his brow, perplexed. "What he must have is a special field of some sort that lowers the wave-length and the intensity. He's getting natural cosmics all the time and taking care of them."

"That wouldn't be much of a trick," Russ pointed out. "But when he takes care of cosmics backed by five billion horsepower ... that's something else!"

Greg grinned wickedly. "I'm going to hand him a long heat radiation. If his field shortens that any, he'll have radio beam and that will blow photo-cells all to h.e.l.l."