Facing destruction, Earth's last immortals sent an emissary through time to alter history. Thus, he appeared in 1952, searching for the-- CHILDREN of the CHRONOTRON By S. J. Byrne [Transcriber's Note: This etext was produced from Imagination Stories of Science and Fantasy December 1952 Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] _When their sun began to wane, the Xlarnans at first retreated underground to hoard the heat and life-supporting energies which their nuclear generators could supply. But as their world grew colder, century after century, they devised a means of creating a substitute for the ionosphere--a protective layer of radioactive gases in the upper reaches of the sky which could warm them by means of its slow, controlled reaction, give them eternal light, and yet absorb its own harder radiations._ _Thus--a planetary cell of life, isolated from the universe, independent of solar heat. And the Xlarnans at last emerged from their subterranean cities to take up life anew in a tropical Paradise that knew neither nightfall nor seasons. They missed the starlit night skies of old, the sunrises and sunsets, and most of all the stupendous celestial rainbow, the Great Ring, which some of them believed to be formed of the particles of a large satellite that had encircled their world back in the dim Beginning._ _But the time arrived when they knew they were losing control of their reaction sphere in the sky. The hard radiations increased inexorably in spite of all the coolants they could generate and send aloft. They had to admit that the day would come when they would be destroyed by the very instrument that had given them an extra hundred millenniums of life._ _At the end of time--the Xlarnans, pressed against a wall, the reaction sphere, from which came hard radiations, burning them. The ethnic urge to survive in the face of swiftly approaching death. Necessity mothering invention. And then--_ _The Chronotron...._ _Electronic envelopes speeding faster than light. Three dimensional nature rejecting the envelope. Only in Time can anything be in two places--along the duration line._ _The Chronotron--planting new Cause in the beginning of Effect. And there is alternate time._ _Large numbers of Xlarnans, through the Chronotron, back to the beginning of the reaction sphere era, an already advanced race with the course of another hundred thousand years to run before facing the threat from the sky once more._ _The first cycle ends, and at the last extremity of alternate time veritable super beings achieve immortality. With immortality, less procreation. And at last, sterility._