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 massed
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'di