The most important of the three was the discovery of sub-spectrum rays. These were hitherto unsuspected octaves of electromagnetic radiation far below even the gamma and cosmic rays in wavelength, and which had velocities vastly greater than the speed of light.

Of these sub-spectrum rays the most useful were the so-called pressure rays in the Minus-30th octave of the spectrum, which could react against the tenuous cosmic dust of space with a powerful pressure. These pressure rays formed the driving power of star-ships. They were produced in generators powered by atomic turbines, and were jetted from the stern of a ship to drive it thousands of times faster than light.

The second vital invention was that of the mass-control. Einstein's equations had shown that if a ship traveled as fast as light, its mass would expand to infinity. This difficulty was overcome by the mass-control, which “bled” off mass as energy to maintain a constant mass unaltered by velocity. The energy thus obtained was stored in accumulators and fed back automatically whenever speed was reduced.

The final invention concerned the human element, Men's bodies would have been unable ordinarily to withstand those vast accelerations, but this obstacle was conquered by the cradlestasis. This was a stasis of force which gripped every atom in a ship. The energy-drive jets gave their thrust, not to the ship directly, but to its stasis. Thus everyone and everything in the ship remained unaffected by acceleration. Magnetic apparatus furnished artificial gravity on shipboard, similar to that of the tiny gravitation-equalizers worn by all star-travelers.

The fastest of the sub-spectrum rays, those of the Minus-42nd Octave, were so speedy that they made light seem to crawl. These super-speed rays were used in telestereo communication and also in the vital function of radar for the starships.

Using these inventions to build star-ships, mankind took at once to interstellar space. Alpha Centauri, Sirius and Altair were quickly visited.

Colonies were soon established on suitable star-worlds. For some 10,000 years, Sol and Earth remained the center of government of a growing region of colonized stars.

Until then, there had been no serious conflicts. Aboriginal alien races of intelligence had been found at some star-systems and were helped and educated, but there was found no scientific civilization on any star-world. That had been expected, for if such a race existed it would have visited us long before we ourselves had conquered space.

But in the year 12,455, a group of star-systems near Polaris complained that Earth was too remote to appreciate their problems, and they set up an independent kingdom. By 39,000, the kingdoms of Lyra, Cygnus, and the Baronies of the great Hercules Cluster had declared independence.

Criminals and fugitives from the law seeking refuge in the Cloud eventually founded the League of Dark Worlds. By 120,000, the star-kingdoms were many. But the biggest was still the Mid-Galactic Empire, and hosts of star-worlds remained loyal to it. For convenience its government had been shifted in 62,339 from Earth to a world of the great sun Canopus.

The Empire took the lead of the star-kingdoms in the year 129,411 when the galaxy was suddenly invaded by alien and powerful creatures from the Magellanic Clusters outside. And after that invasion was repelled the Empire had steadily grown by exploring and colonizing the wild, unmapped star-systems in the frontier regions called the Marches of Outer Space.

Thus when Gordon found himself in the galaxy of this year 202,115, he found its star-kingdoms already old in traditions and history. Many wars had been fought between them, but the Empire had steadily sought to prevent such sanguine galactic struggles and to unify them in peace. But now the ominous growth of the League of Dark Worlds had reached a point where the safety of the Empire itself was challenged.

Vel Quen finally told Gordon, “I know you want to see much of our civilization before you return to your own body and time. First let me show you what Earth looks like now. Stand upon this plate.”

He referred to one of two round quartz plates set in the floor, which were part of a curious, complex apparatus.

“This is a telestereo, which projects and receives stereoscopic images that can see and hear,” Vel Quen explained. “It operates almost instantaneously over any distance.”

Gordon stood gingerly with him on the quartz plate. The old scientist touched a switch.

Abruptly, Gordon seemed to be in another place. He knew he was still in the tower laboratory, but a seeing, hearing image of himself now stood on a stereo-receiver on a terrace high in a great city.

“This is Nyar, largest city of Earth,” said Vel Quen. “Of course, it cannot compare with the metropoli of the great star-worlds.”

Gordon gasped. He was looking out over a mammoth city of terraced white pyramids.

Far out beyond it he could glimpse a spaceport, with rows of sunken docks and long, fishlike star-ships in them. There were also a few massive, grim looking warships with the Empire's comet emblem on them.

But it was the great city itself that held his stunned gaze. Its terraces were flowering green gardens with gay awnings and crowds of pleasure-seeking people.

Vel Quen switched them to other stereo-receivers in Nyar. He had glimpses of the interior of the city, of halls and corridors, of apartments and workshops, of giant underground atomic power plants.

The scene suddenly vanished from John Gordon's fascinated eyes as Vel Quen snapped off the telestereo and darted toward a window.

“There is a ship coming!” he said. “I can't understand it. No ship ever lands here.”

Gordon heard a droning in the air and glimpsed a long, slim, shining craft dropping out of the sky toward the lonely tower.

Vel Quen looked alarmed. “It's a warship, a phantom-cruiser, but has no emblem on it. There's something wrong about this!”

The shining ship landed with a rush on the plateau a quarter-mile from the tower. A door in its side instantly slid open.

From it poured a score of gray uniformed, helmeted men who carried weapons like long, slim-barreled pistols, and who advanced in a run toward the tower.

“They wear the uniform of Empire soldiers but they should not have come here,” Vel Quen said. His wrinkled face was puzzled and worried. “Could it be-”

He broke off, seeming to reach a sudden decision. “I am going to notify the Nyar naval base at once!”

As the old scientist turned from John, Gordon toward the telestereo, there came a sudden loud crash below.

“They have blasted in the door!” cried Vel Quen. “Quick, John Gordon, take the-”

Gordon never learned what he meant to tell him. For at that moment, the uniformed men came rushing up the stair into the room.

They were strange-looking men. Their faces were white, a pallid, colorless and unnatural white.

“League soldiers!” said Vel Quen, the instant he saw them thus close. He whirled to turn on the telestereo.

The leader of the invaders raised his long, slim pistol. A tiny pellet flicked from it and buried itself in Vel Quen's back. It instantly exploded in his body. The old scientist dropped in his tracks.

Until that moment, ignorance and bewilderment had held Gordon motionless. But he felt a hot rage burst along his nerves as he saw Vel Quen fall. He had come to like the old scientist, in these days.

With a fierce exclamation, Gordon plunged forward. One of the uniformed men instantly raised his pistol.

“Don't blast him-it's Zarth Arn himself,” yelled the officer who had shot down Vel Quen. “Grab him.”

Gordon got his fists home on the face of one of them, but that was all. A dozen hands grasped him, his arms were twisted behind his back, and he was held as helpless as a raging child.