Rodis and Hilar had climbed from their natal caverns to the top chamber of the high observatory tower. Pressed close together, for warmth as well as love, they stood at an eastern window looking forth on hills and valleys dim with perennial starlight. They had come up to watch the rising of the sun: that sun which they had never seen except as an orb of blackness, occluding the zodiacal stars in its course from horizon to horizon.

Thus their ancestors had seen it for millenniums. By some freak of cosmic law, unforeseen, and inexplicable to astronomers and physicists, the sun's cooling had been comparatively sudden, and the earth had not suffered the long-drawn complete desiccation of such planets as Mercury and Mars. Rivers, lakes, seas, had frozen solid; and the air itself had congealed, all in a term of years historic rather than geologic. Millions of the earth's inhabitants had perished, trapped by the glacial ice, the centigrade cold. The rest, armed with all the resources of science, had found time to entrench themselves against the cosmic night in a world of ramified caverns, dug by atomic excavators far below the surface.

Here, by the light of artificial orbs, and the heat drawn from the planet's still-molten depths, life went on much as it had done in the outer world. Trees, fruits, grasses, grains, vegetables, were grown in isotope-stimulated soil or hydroroponic gardens, affording food, renewing a breathable atmosphere. Domestic animals were kept; and birds flew; and insects crawled or fluttered. The rays considered necessary for life and health were afforded by the sunbright lamps that shone eternally in all the caverns.

Little of the old science was lost; but, on the other hand, there was now little advance. Existence had become the conserving of a fire menaced by inexorable night. Generation by generation a mysterious sterility had lessened the numbers of the race from millions to a few thousands. As time went on, a similar sterility began to affect animals; and even plants no longer flourished with their first abundance. No biologist could determine the cause with certainty.

Perhaps man, as well as other terrestrial life-forms, was past his crime, and had begun to undergo collectively the inevitable senility that comes to the individual. Or perhaps, having been a surface-dweller throughout most of his evolution, he was inadaptable to the cribbed and prisoned life, the caverned light and air; and was dying slowly from the deprivation of things he had almost forgotten.

Indeed, the world that had once flourished beneath a living sun was little more than a legend now, a tradition preserved by art and literature and history. Its heeding Babelian cities, its fecund hills and plains, were swathed impenetrably in snow and ice and solidified air. No living man and gazed upon it, except from the night-bound towers maintained as observatories.

Still, however, the dreams of men were often lit by primordial memories, in which the sun shone on rippling waters and waving trees and grass. And their waking hours were sometimes touched by an undying nostalgia for the lost earth. . . .

Alarmed by the prospect of racial extinction, the most able and brilliant savants had conceived a project that was seemingly no less desperate than fantastic. The plan, if executed, might lead to failure or even the planet's destruction. But all the necessary steps had now been taken toward its launching.

It was of this plan that Rodis and Hilar spoke, standing clasped in each other's arms, as they waited for the rising of the dead sun.

"And you must go?" said Rodis, with averted eyes and voice that quavered a little.

"Of course. It is a duty and an honor. I am regarded as the foremost of the younger atomicists. The actual placing and timing of the bombs will devolve largely upon me."

"But—are you sure of success? There are so many risks, Hilar." The girl shuddered, clasping her lover with convulsive tightness.

"We are not sure of anything," Hilar admitted. "But, granting that our calculations are correct, the multiple charges of fissionable materials including more than half the solar elements, should start chain-reactions that will restore the sun to its former incandescence. Of course, the explosion may be too sudden and too violent, involving the nearer planets in the formation of a nova. But we do not believe that this will happen —since an explosion of such magnitude would require instant disruption of all the sun's elements. Such disruption should not occur without a starter for each separate atomic structure. Science has never been able to break down all the known elements. If it had been, the earth itself would undoubtedly have suffered destruction in the old atomic wars."

Hilar paused, and his eyes dilated, kindling with a visionary fire.

"How glorious," he went on, "to use for a purpose of cosmic renovation the deadly projectiles designed by our forefathers only to blast and destroy. Stored in sealed caverns, they have not been used since man abandoned the earth's surface so many millenniums ago. Nor have the old spaceships been used either. . . . An interstellar drive was never perfected; and our voyagings were always limited to the other worlds of our own system—none of which was inhabited, or inhabitable. Since the sun's cooling and darkening, there has been no object in visiting any of them. But the ships too were stored away. And the newest and speediest one, powered with anti-gravity magnets, has been made ready for our voyage to the sun."

Rodis listened silently, with an awe that seemed to have subdued her misgivings, while Hilar continued to speak of the tremendous project upon which he, with six other chosen technicians, was about to embark. In the meanwhile, the black sun rose slowly into heavens thronged with the cold ironic blazing of innumerable stars, among which no planet shone. It blotted out the sting of the Scorpion, poised at that hour above the eastern hills. It was smaller but nearer than the igneous orb of history and legend. In its center, like a Cyclopean eye, there burned a single spot of dusky red fire, believed to mark the eruption of some immense volcano amid the measureless and cinder-blackened landscape.

To one standing in the ice-bound valley below the observatory, it would have seemed that the tower's litten window was a yellow eye that stared back from the dead earth to that crimson eye of the dead sun.

"Soon," said Hilar, "you will climb to this chamber—and see the morning that none has seen for a century of centuries. The thick ice will thaw from the peaks and valleys, running in streams to remolten lakes and oceans. The liquefied air will rise in clouds and vapors, touched with the spectrum-tinted splendor of the light. Again, across earth, will blow the winds of the four quarters; and grass and flowers will grow, and trees burgeon from tiny saplings. And man, the dweller in closed caves and abysses, will return to his proper heritage."

"How wonderful it all sounds," murmured Rodis. "But . . . you will come back to me?"

"I will come back to you . . . in the sunlight," said Hilar. The space-vessel Phosphor lay in a huge cavern beneath that region which had once been known as the Atlas Mountains. The cavern's mile-thick roof had been partly blasted away by atomic disintegrators. A great circular shaft slanted upward to the surface, forming a mouth in the mountain-side through which the stars of the Zodiac were visible. The prow of the Phosphor pointed at the stars.

All was now ready for its launching. A score of dignitaries and savants, looking like strange ungainly monsters in suits and helmets worn against the spatial cold that had invaded the cavern, were present for the occasion. Hilar and his six companions had already gone aboard the Phosphor and had closed its air-locks.

Inscrutable and silent behind their metalloid helmets, the watchers waited. There was no ceremony, no speaking or waving of farewells; nothing to indicate that a world's destiny impended on the mission of the vessel.

Like mouths of fire-belching dragons the stern-rockets flared, and the Phosphor, like a wingless bird, soared upward through the great shaft and vanished. Hilar, gazing through a rear port, saw for a few moments the lamp- bright window of that tower in which he had stood so recently with Rodis. The window was a golden spark that swirled donward in abysses of devouring night—and was extinguished. Behind it, he knew, his beloved stood watching the Phosphor's departure. It was a symbol, he mused . . . a symbol of life, of memory . . . of the suns themselves . . . of all things that flash briefly and fall into oblivion.

But such thoughts, he felt, should be dismissed. They were unworthy of one whom his fellows had appointed as a light-bringer, a Prometheus who should rekindle the dead sun and re-lumine the dark world. There were no days, only hours of eternal starlight, to measure the time in which they sped outward through the void. The rockets, used for initial propulsion, no longer flamed astern; and the vessel flew in darkness, except for the gleaming Argus eyes of its ports, drawn now by the mighty gravitational drag of the blind sun. Test-flights had been considered unnecessary for the Phosphor. All its machinery was in perfect condition; and the mechanics involved were simple and easily mastered. None of its crew had ever been in extraterrestrial space before; but all were well-trained in astronomy, mathematics, and the various techniques essential to a voyage between worlds. There were two navigators; one rocket-engineer; and two engineers who would operate the powerful generators, charged with a negative magnetism reverse to that of gravity, with which they hoped to approach, circumnavigate, and eventually depart in safety from an orb enormously heavier than the system's nine planets merged into one. Hilar and his assistant, Han Joas, completed the personnel. Their sole task was the timing, landing, and distribution of the bombs.

All were descendants of a mixed race with Latin, Semitic, Hamitic, and negroid ancestry: a race that had dwelt, before the sun's cooling, in countries south of the Mediterranean, where the former deserts had been rendered fertile by a vast irrigation-system of lakes and canals.

This mixture, after so many centuries of cavern life, had produced a characteristically slender, well-knit type, of short or medium stature and pale olive complexion. The features were often of negroid softness, the general physique was marked by a delicacy verging upon decadence.

To an extent surprising, in view of the vast intermediate eras of historic and geographic change, this people had preserved many preatomic traditions and even something of the old classic Mediterranean cultures. Their language bore distinct traces of Latin, Greek, Spanish and Arabic.

Remnants of other peoples, those of sub-equatorial Asia and America, had survived the universal glaciation by burrowing underground. Radio communication had been maintained with these peoples till within fairly recent times, and had then ceased. It was believed that they had died out, or had retrograded into savagery, losing the civilization to which they had once attained.

Hour after hour, intervaled only by sleep and eating, the Phosphor sped onward through the black unvarying void. To Hilar, it seemed at times that they flew merely through a darker and vaster cavern whose remote walls were spangled by the stars as if by radiant orbs. He had thought to feel the overwhelming vertigo of unbottomed and undiretioned space. Instead, there was a weird sense of circumscription by the ambient night and emptiness, together with a sense of cyclic repetition, as if all that was happening had happened many times before and must recur often through endless future kalpas.

Had he and his companions gone forth in former cycles to the relighting of former perished suns? Would they go forth again, to rekindle suns that would flame and die in some posterior universe? Had there always been, would there always be, a Rodis who awaited his return? Of these thoughts he spoke only to Han Joas, who shared something of his innate mysticism and his trend toward cosmic speculation. But mostly the two talked of the mysteries of the atom and its typhonic powers, and discussed the problems with which they would shortly be confronted.

The ship carried several hundred disruption bombs, many of untried potency: the unused heritage of ancient wars that had left chasm scars and lethal radioactive areas, some a thousand miles or more in extent, for the planetary glaciers to cover. There were bombs of iron, calcium, sodium, helium, hydrogen, sulphur, potassium, magnesium, copper, chromium, strontium, barium, zinc: elements that had all been ancientily revealed in the solar spectrum. Even at the apex of their madness, the warring nations had wisely refrained from employing more than a few such bombs at any one time. Chain-reactions had sometimes been started; but, fortunately, had died out. Hilar and Han Joas hoped to distribute the bombs at intervals over the sun's entire circumference; preferably in large deposits of the same elements as those of which they were composed. The vessel was equipped with radar apparatus by which the various elements could be detected and located. The bombs would be timed to explode with as much simultaneity as possible. If all went well, the Phosphor would have fulfilled its mission and traveled most of the return distance to earth before the explosions occurred.

It had been conjectured that the sun's interior was composed of still- molten magma, covered by a relatively thin crust: a seething flux of matter that manifested itself in volcanic activities. Only one of the volcanoes was visible from earth to the naked eye; but numerous others had been revealed to telescopic study. Now, as the Phosphor drew near to its destination, the others flamed out on the huge, slowly rotating orb that had darkened a fourth of the ecliptic and had blotted Libra, Scorpio and Sagittarius wholly from view.

For a long time it had seemed to hang above the voyagers. Now, suddenly, as if through some prodigious legerdemain, it lay beneath them: a monstrous, ever-broadening disk of ebon, eyed with fiery craters, veined and spotted and blotched with unknown pallid radioactives. It was like the buckler of some macrososmic giant of the night, who had entrenched himself in the abyss lying between the worlds.

The Phosphor plunged toward it like a steel splinter drawn by some tremendous lodestone.

Each member of the crew had been trained before-hand for the part he was to play; and everything had been timed with the utmost precision. Sybal and Samac, the engineers of the anti-gravity magnets, began to manipulate the switches that would build up resistance to the solar drag. The generators, bulking to the height of three men, with induction-coils that suggested some colossal Laocoon, could draw from cosmic space a negative force capable of counteracting many earth-gravities. In past ages they had defied easily the pull of Jupiter; and the ship had even coasted as near to the blazing sun as its insulation and refrigeration systems would safely permit. Therefore it seemed reasonable to expect that the voyagers could accomplish their purpose of approaching closely to the darkened globe, of circling it, and pulling away when the disruption-charges had all been planted.

A dull, subsonic vibration, felt rather than heard, began to emanate from the magnets. It shook the vessel, ached in the voyagers' tissues. Intently, with anxiety unbetrayed by their impassive features, they watched the slow, gradual building-up of power shown by gauge-dials on which giant needles crept like horologic hands, registering the reversed gravities one after one, till a drag equivalent to that of fifteen Earths had been neutralized. The clamp of the solar gravitation, drawing them on with projectile-like velocity, crushing them to their seats with relentless increase of weight, was loosened. The needles crept on . . . more slowly now . . . to sixteen . . . to seventeen . . . and stopped. The Phosphor's fall had been retarded but not arrested. And the switches stood at their last notch.

Sybal spoke, in answer to the unuttered questions of his companions. "Something is wrong. Perhaps there has been some unforeseen deterioration of the coils, in whose composition strange and complex alloy were used. Some of the elements may have been unstable—or have developed instability through age. Or perhaps there is some interfering force, born of the sun's decay. At any rate, it is impossible to build more power toward the twenty-seven antigravities we will require close to the solar surface."

Samac added: "The decelerative jets will increase our resistance to nineteen anti-gravities. It will still be far from enough, even at our present distance."

"How much time have we ?" inquired Hilar, turning to the navigators, Calaf and Caramod.

The two conferred and calculated.

"By using the decelerative jets, it will be two hours before we reach the sun," announced Calaf finally.

As if his announcement had been an order, Eibano, the jet-engineer, promptly jerked the levers that fired to full power the reversing rockets banked in the Phosphor's nose and sides. There was a slight further deceleration of their descent, a further lightening of the grievious weight that oppressed them. But the Phosphor still plunged irreversibly sun-ward.

Hilar and Han Joas exchanged a glance of understanding and agreement. They rose stiffly from their seats, and moved heavily toward the magazine, occupying fully half the ship's interior, in which the hundreds of disruption-bombs were racked. It was unnecessary to announce their purpose; and no one spoke either in approval or demur.

Hilar opened the magazine's door; and he and Han Joas paused on the threshold, looking back. They saw for the last time the faces of their fellow-voyagers, expressing no other emotion than resignation, vignetted, as it were, on the verge of destruction. Then they entered the magazine, closing its door behind them.

They set to work methodically, moving back to back along a narrow aisle between the racks in which the immerse ovoid bombs were piled in strict order according to their respective elements. Because of various coördinated dials and switches involved, it was a matter of minutes to prepare a single bomb for the explosion. Therefore Hilar and Han Joas, in the time at their disposal, could do no more than set the timing and detonating mechanism of one bomb of each element. A great chronometer, ticking at the magazine's farther end, enabled them to accomplish this task with precision. The bombs were thus timed to explode simultaneously, detonating the others through chain-reaction, at the moment when the Phosphor should touch the sun's surface.

The solar pull, strengthening as the Phosphor fell to its doom, had now made their movements slow and difficult. It would, they feared, immobilize them before they could finish preparing a second series of bombs for detonation. Laboriously, beneath the burden of a weight already trebled, they made their way to seats that faced a reflector in which the external cosmos was imaged.

It was an awesome and stupendous scene on which they gazed. The sun's globe had broadened vastly, filling the nether heavens. Half-seen, a dim unhorizoned landscape, fitfully lit by the crimson far-sundered flares of volcanoes, by bluish zones and patches of strange radio-active minerals, it deepened beneath them abysmally disclosing mountains that would have made the Himalayas seem like hillocks, revealing chasms that might have engulfed asteroids and planets.

At the center of this Cyclopean landscape burned the great volcano that had been called Hephaestus by astronomers. It was the same volcano watched by Hilar and Rodis from the observatory window. Tongues of flame a hundred miles in length arose and licked skyward from a crater that seemed the mouth of some ultramundane hell.

Hilar and Han Joas no longer heard the chronometer's portentous ticking, and had no eyes for the watching of its ominous hands. Such watching was needless now: there was nothing more to be done, and nothing before them but eternity. They measured their descent by the broadening of the dim solar plain, the leaping into salience of new mountains, the deepening of new chasms and gulfs in the globe that had now lost all semblance of a sphere.

It was plain now that the Phosphor would fall directly into the flaming and yawning crater of Hephaestus. Faster and faster it plunged, heavier grew the piled chains of gravity that giants could not have lifted. . .

At the very last, the reflector of which Hilar and Han Joas peered was filled entirely by the tongued volcanic fires that enveloped the Phosphor.

Then, without eyes to see or ears to apprehend, they were part of the pyre from which the sun, like a Phoenix, was reborn.

Rodis, climbing to the tower, after a period of fitful sleep and troublous dreams, saw from its window the rising of the rekindled orb.

It dazzled her, though its glory was half-dimmed by rainbow-colored mists that fumed from the icy mountain-tops. It was a sight filled with marvel and with portent. Thin rills of downward-threading water had already begun to fret the glacial armor on slopes and scarps; and later they would swell to cataracts, laying bare the buried soil and stone. Vapors, that seemed to flow and fluctuate on renascent winds, swam sun-ward from lakes of congealed air at the valley's bottom. It was a visible resumption of the elemental life and activity so long suspended in hibernal night. Even through the tower's insulating walls, Rodis felt the solar warmth that later would awaken the seeds and spores of plants that had lain dormant for cycles.

Her heart was stirred to wonder by the spectacle. But beneath the wonder was a great numbness and a sadness like unmelting ice. Hilar, she knew, would never return to her—except as a ray of the light, a spark of the vital heat, that he had helped to relumine. For the nonce, there was irony rather than comfort in the memory of his promise: "I will come back to you—in the sunlight."