"I haven't been doing much, Honey," he told her hesitantly, and not too convincingly. "You'd better just run along home to bed. Research causes accidents once in a while. I'll get everything straightened out all right." But in the reflected rays of the flashlight, the girl's face and eyes were determined. "I won't go, Sam," she said very definitely, "until I find out that everything is all right. First place, you're hurt, and I'd be stubborn for your sake. But there's more. That glow in the sky. That smell of ozone--not only here, but everywhere here.... What does it all mean, Sam?" Conway looked nervously toward the heavens. Yes, he could see a halo of light, sure enough. He had thought it was only the diffusion of starshine by the moisture in the atmosphere. Now he knew better. It was a little too bright and too low to be an aurora. It could be _like_ an aurora, of course, something electrical and yet not quite the real, normal thing. The breeze outside bore a slight yet unmistakable pungence of ozone too. It was just as Ellen had said. The gas was not only in the lab. It was here, too, as though all the atmosphere in the neighborhood had been affected by some electrical process. "Listen!" Ellen said suddenly. Sam strained his ears. At first he could detect nothing at all. Then he noticed a dim, lonely humming, that seemed to emanate from the ground, and from the bricks of the laboratory. The sound seemed to be getting gradually louder. It made Sam shudder with the mystery of hidden things. And he began to feel, too, a sharp ache in his muscles, quite distinct from the soreness of his minor injury. Suspicion grew on him again; suspicion that his latest experiment had been not entirely without lasting effect. Something _had_ happened! Something had been started after all! Sam grasped Ellen by the arm. "Come inside, Ellen," he said. "I've got to make a few tests." He did this very quickly, working in the beam of his flashlight, which the girl held for him. Meanwhile he made a complete confession, telling her what he'd found on Mars and what he'd been doing. He found now that he couldn't keep an electroscope charged. This meant that the air was ionized--that it would promptly conduct away any electrical charge that the instrument might hold. And atmospheric ionization meant, or could mean, the presence of radioactivity--of atomic disturbances. He tried exposing a bit of photographic film in the dark. In the developing fluids it turned entirely black. There were strong invisible rays then, to affect it; rays coming from the walls, the ground, the very air itself perhaps. Rays probably from bursting atoms. The sound--the humming--must be some incidental phenomenon of their breakdown. Dully Sam felt of the walls. Their temperature was already higher than that of the air and they vibrated distinctly with that steady hum. Sam's whole body felt hot, as though a strange flame was blazing in his own flesh.