The sunlight died, and dusk began and deepened, and vividly brilliant stars began to come out overhead, and Tommy suddenly searched the heavens eagerly for familiar constellations. And found not one. All the stars were strange. These stars seemed larger and much more near than the tiny pinpoints that blink down upon our earth.

And then he swung the instrument again and saw great fires roaring and the Ragged Men crouched about them. Within them, rather, because they had built fires about themselves as if to make a wall of flame. And once Tommy saw twin, monstrous eyes, gazing from the blackness of the tree-fern forest. They were huge eyes, and they were far apart, so that the head of the creature who used them must have been enormous.

And they were all of fifteen feet above the ground when they speculatively looked over the ring of fires and the ragged, degraded men within them. Then that creature, whatever it was, turned away and vanished.

But Tommy felt a curious shivering horror of the thing. It had moved soundlessly, without a doubt, because not one of the Ragged Men had noted its presence. It had been kept away by the fires. But Denham and Evelyn were somewhere in the tree-fern forest, and they would not dare to make fires....

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.

"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!"

He set a little tin can beneath the peculiar device of copper-tubing rings. The can was wholly ordinary, made of thin sheet-iron plated with tin as are all the tin cans of commerce.

"You have the catapult remade?" gasped Von Holtz. "Wait! Wait! Let me look at it!"

For one instant, and one instant only, Tommy let him see. The ma.s.sed set of concentric rings, each one of them parallel to all the others.

It looked rather like a flat coil of tubing; certainly like no particularly obscure form of projector. But as Von Holtz's weak eyes fastened avidly upon it, Tommy pressed the improvised electric switch.

At once that would energize the solenoid and release all the tensed springs from their greater tension, for an attempt to reach a permanent equilibrium.

As Von Holtz and the blue-jowled man stared, the little tin can leaped upward into the tiny coil. The small copper rings twinkled one within the other as the springs operated. The tin can was wrenched this way and that, then for the fraction of a second hurt the eyes that gazed upon it--and it was gone! And then the little coil came spinning down to the work bench top from its broken bearings and the remaining copper rings spun aimlessly for a moment. But the third ring of whitish metal had vanished utterly, and so had the coiled-wire springs which Von Holtz had been unable to distinguish. And there was an overpowering smell of ammonia in the room.

Von Holtz flung himself upon the still-moving little instrument. He inspected it savagely, desperately. His full red lips drew back in a snarl.

"How did you do it?" he cried shrilly. "You must tell me! I--I--I will kill you if you do not tell me!"

The blue-jowled man was watching Von Holtz. Now his lips twisted disgustedly. He turned to Tommy and narrowed his eyes.

"Look here," he rumbled. "This fool's no good! I want the secret of that trick you did. What's your price?"

"I'm not for sale," said Tommy, smiling faintly.

The blue-jowled man regarded him with level eyes.

"My name's Jacaro," he said after an instant. "Maybe you've heard of me. I'm from Chicago."

Tommy smiled more widely.

"To be sure," he admitted. "You were the man who introduced machine-guns into gang warfare, weren't you? Your gunmen lined up half a dozen of the Buddy Haines gang against a wall and wiped them out, I believe. What do you want this secret for?"

The level eyes narrowed. They looked suddenly deadly.

"That's my business," said Jacaro briefly. "You know who I am. And I want that trick y'did. I got my own reasons. I'll pay for it. Plenty.

You know I got plenty to pay, too. Or else--"

"What?"

"Something'll happen to you," said Jacaro briefly. "I ain't sayin''

what. But it's d.a.m.n likely you'll tell what I want to know before it's finished. Name your price and be d.a.m.n quick!"