Tommy drew away from the dimensoscope, shivering. He had been looking only, but the place into which he looked was real, and the dangers that lay hidden there were very genuine, and there was a man and a girl of his own race and time struggling desperately, without arms or hope, to survive. * * * * * Smithers was casually fitting together an intricate array of little rings made of copper tubing. There were three of them, and each was fitted into the next largest by pins which enabled them to spin noiselessly and swiftly at the touch of Smithers' finger. He had them spinning now, each in a separate direction, and the effect was bewildering. As Tommy watched, Smithers stopped them, oiled the pins carefully, and painstakingly inserted a fourth ring. Only this ring was of a white metal that looked somehow more pallid than silver. It had a whiteness like that of ivory beneath its metallic gleam. Tommy blinked. "Did Von Holtz give you that metal?" he asked suddenly. Smithers looked up and puffed at a short brown pipe. "Nope. There was some splashes of it by the castin' box. I melted 'em together an' run a ring. Pressed it to shape; y' can't hammer this stuff. It goes to water and dries up quicker'n lightning--an' you hold y'nose an' run. I used it before for the Professor." Tommy went over to him excitedly. He picked up the little contrivance of many concentric rings. The big motor was throbbing rhythmically, and the generator was humming at the back of the laboratory. Von Holtz was out of sight. * * * * * With painstaking care Tommy went over the little device. He looked up. "A coil?" "I wound one," said Smithers calmly. "On the lathe. Not so hot, but it'll do, I guess. But I can't fix these rings like the Professor did." "I think I can," said Tommy crisply. "Did you make some wire for springs?" "Yeah!" Tommy fingered the wire. Stout, stiff, and surprisingly springy wire of the same peculiar metal. It was that metallic ammonium which chemists have deduced must exist because of the chemical behavior of the compound NH3, but which Denham alone had managed to procure. Tommy deduced that it was an allotropic modification of the substance which forms an amalgam with mercury, as metallic tin is an allotrope of the amorphous gray powder which is tin in its normal, stable state. He set to work with feverish excitement. For one hour, for two he worked. At the end of that time he was explaining the matter curtly to Smithers, so intent on his work that he wholly failed to hear a motor car outside or to realize that it had also grown dark in this world of ours.