"Wait a minute!" broke in Larry excitedly. "For once I beat you to the draw. I guessed it in the museum. These jaspers of the 260th Century are not only _unable_ to hear, they're _afraid_ to hear! They wear those leather headgears because they have to. Because something had made them extremely sensitive to percussion." "And I know," chimed in the girl positively, "what caused it. It was the change!" "Change?" "Yes. You've noticed the sky, haven't you? Didn't you see something strange about it?" Larry thought for a moment. Then, "The sun! There isn't any sun." "There is a sun," cried the girl, "but you can't see it. It's concealed behind a huge dome of _impervite_--a sort of leaded, polarized glass. Harg told me all about it while you were unconscious. "In the year 17,000 A.D., or thereabouts, there was a terrible catastrophe on Earth. Man's constant drainage of electrical energy created a rupture in the Heaviside layer, and the layer collapsed. As you know, the Heaviside layer is Earth's only protection against potentials from space, from the undiluted strength of the Milliken rays. * * * * * "Without that protection, life on Earth was doomed. So large areas were domed over with this sixty-foot-thick layer of _impervite_. And--" "And in the meantime," interrupted Larry, "intense subjection to cosmic radiation, along with the increasing use of telepathy, turned the human race's hearing apparatus from a useful organ into a vestigial one." "And one," agreed the girl, "sensitive as the nerve of a tooth. It must be that. It couldn't be anything else. So there is Harg's weakness. Now, if we can only find some way to play upon it--" Larry said gloomily, "But he still is the only one who can return us to our own time." Sandra's hand touched his swiftly, confidently. "We'll find some way to make him," she whispered. "We'll do it, you and I--" Even under these circumstances Larry Wilson found the touch of that hand thrilling, the confidence of Sandra's voice, with its "you and I," endearing. It was a jest of the gods that this new glory should have come to him at last in such a situation. But the year mattered little. Time or no Time, he knew, and he thought she knew-- "Sandra," he said, "there is one thing--" "Shhh!" she cautioned suddenly. "Footsteps!" The metallic doorpane slid back, and once again Harg entered the room, this time accompanied by a pair of diminutive companions garbed in plainer, cruder harness than that of the scientist. Larry made an effort to expunge all thought from his mind, fearful that the man of the future might read his new determination. But Harg smiled easily. "You will come with me now, Miss Day." Instantly Larry was on the alert. "Where are you taking her?" "It is not yours to ask, savage," said Harg curtly. "But reassure yourself. She will come to no harm."