“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.
“You see, Smithers, if a two-dimensioned creature wanted to adjust two right angles at right angles to each other, he’d have them laid flat, of course. And if he put a spring at the far ends of those right angles—they’d look like a T, put together—so that the cross-bar of that T was under tension, he’d have the equivalent of what I’m doing. To make a three-dimensioned figure, that imaginary man would have to bend one side of the cross-bar up. As if the two ends of it were under tension by a spring, and the spring would only be relieved of tension when that cross-bar was bent. But the vertical would be his time dimension, so he’d have to have something thin, or it couldn’t be bent. He’d need something ‘thin in time.’
“We have the same problem. But metallic ammonium is ‘thin in time.’ It’s so fugitive a substance that Denham is the only man ever to secure it. So we use these rings and adjust these springs to them so they’re under tension which will only be released when they’re all at right angles to each other. In our three dimensions that’s impossible, but we have a metal that can revolve in a fourth, and we reinforce their tendency to adjust themselves by starting them off with a jerk. We’ve got ’em flat. They’ll make a good stiff jerk when they try to adjust themselves. And the solenoid’s a bit eccentric—”
“Shut up!” snapped Smithers suddenly.
He was facing the door, bristling. Von Holtz was in the act of coming in, with a beefy, broad-shouldered man with blue jowls. Tommy straightened up, thought swiftly, and then smiled grimly.
“Hullo, Von Holtz,” he said pleasantly. “We’ve just completed a model catapult. We’re all set to try it out. Watch!”