came down in the flowing flood of spilled detergent, flat on his stomach, and with marked forward momentum. He slid. The floor of the plant had recently been oiled to keep down dust. The coefficient of friction of a really good detergent on top of floor-oil is remarkably low,—somewhere around point oh-oh-nine. Hood number two slid magnificently on his belly on the superb lubrication afforded by detergent on top of floor-oil.

The first hood staggered. Something else fell from the shelf. It was a carton of electric-light bulbs. Despite the protecting carton, they went off with crackings like gunfire. Technically, they did not explode but implode, but the hood with the revolver did not notice the difference. He leaped—and also landed in the middle of the wide streak of detergent-over-oil which might have been arranged to receive him.

He remained erect, but he slid slowly along that shining path. His relatively low speed was not his fault, because he went through all the motions of frenzied flight. His legs twinkled as he ran. But his feet slid backward. He moved with a sort of dignified celerity, running fast enough for ten times the speed, upon a surface which had a frictional coefficient far below that of the smoothest possible ice.

Detective Sergeant Fitzgerald gaped, his mouth dropped open and his gun held laxly in a practically nerveless hand.

The thing developed splendidly. The prone gunman slid out of the wide double door, pushing a bow-wave of detergent before him. He slid across the cement just outside, into the open garage whose delivery-truck was absent, and slammed with a sort of deliberate violence into a stack of four cardboard drums of that bone-black which is used to filter cleaning-fluid so it can be used over again in the dry-cleaning machine. The garage was used for storage as well as shelter for the establishment's truck.

The four drums were not accurately piled. They were three and a half feet high and two feet in diameter. They toppled sedately, falling with a fine precision upon the now hatless, running, sliding hood. One of them burst upon him. A second burst upon the prone man—who had butted through the cardboard of the bottom one on his arrival. There was a dense black cloud which filled all the interior of the garage. It was bone-black, which cannot be told from lamp-black or soot by the uninitiated.

From the cloud came a despairing revolver shot. It was pure reflex action by a man who had been whammed over the head by a hundred-and-fifty-pound drum of yielding—in fact bursting—material. There was a metallic clang. Then silence.

In a very little while the dust-cloud cleared. One figure struggled insanely. Upon him descended—from an oil drum of cylinder-oil stored above the rafters—a tranquil, glistening rod of opalescent cylinder-oil. His last bullet had punctured the drum. Oil turned the bone-black upon him into a thick, sticky goo which instantly gathered more bone-black to become thicker, stickier, and gooier. He fought it, while his unconscious companion lay with his head in a crumpled cardboard container of more black stuff.

The despairing, struggling hood managed to get off one more shot, as if defying even fate and chance. This bullet likewise found a target. It burst a container of powdered dye-stuff, also stored overhead. The container practically exploded and its contents descended in a widespread shower which coated all the interior of the garage with a lovely layer of bright heliotrope.

Maybe the struggling hood saw it. If so, it broke him utterly. What had happened was starkly impossible. The only sane explanation was that he had died and was in hell. He accepted that explanation and broke into sobs.

Detective Sergeant Fitzgerald had witnessed every instant of the happening, but he did not believe it. Nevertheless, he said in a strange voice: "I'll phone for the paddy-wagon. It'll do for a ambulance, in case of need."

He put away his unused service revolver. Thinking strange, dizzy thoughts of twitching eyelids and plastic scraps and starkly incredible happenings, he managed to call for the police patrol. When he hung up, he gazed blankly at the wall. He gazed, in fact, at a spot where a peculiar small machine with no visible function reposed—somewhat dusty—on a shelf.

Brink stepped over briskly and closed the door between the scene of catastrophe and the immaculate shop. Somehow, none of the mess had spilled back through the doorway. Then he came in, frowning a little.

"The fight's out of them," he said cheerfully. "One's got a bad cut on his head. The other's completely unnerved. Tsk! Tsk! I hate to have such things happen!"

Sergeant Fitzgerald shook himself, as if trying to come back to a normal and a reasonable world.

"Look!" he said in a hoarse voice. "I saw it, an' I still don't believe it! Things like this don't happen! I thought you might be lucky. It ain't that. I thought I might be crazy. It ain't that! What has been goin' on?"

Brink sat down. His air was one of wry contemplation.

"I told you I had a special kind of luck you couldn't believe. Did your eyelids twitch any time today?"

Fitzgerald swallowed.

"They did. And I stopped short an' something that should've knocked my cranium down my windpipe missed me by inches. An' again—But no matter. Yes."

"Maybe you can believe it, then," said Brink. "Did you ever hear of a man named Hieronymus?"

"No," said Fitzgerald in a numbed voice. "Who's he?"

"He got a patent once," said Brink, matter-of-factly, "on a machine he believed detected something he called eloptic radiation. He thought it was a kind of radiation nobody had noticed before. He was wrong. It worked by something called psi."

Sergeant Fitzgerald shook his head. It still needed clearing.

"Psi still isn't fully understood," explained Brink, "but it will do a lot of things. For instance, it can change probability as magnetism can change temperature. You can establish a psi field in a suitable material, just as you can establish a magnetic field in steel or alnico. Now, if you spin a copper disk in a magnetic field, you get eddy currents. Keep it up, and the disk gets hot. If you're obstinate about it, you can melt the copper. It isn't the magnet, as such, that does the melting. It's the energy of the spinning disk that is changed into heat. The magnetic field simply sets up the conditions for the change of motion into heat. In the same way ... am I boring you?"

"Confusing me," said Fitzgerald, "maybe. But keep on. Maybe I'll catch a glimmer presently."

"In the same way," said Brink, "you can try to perform violent actions in a strong psi field—a field made especially to act on violence. When you first try it you get something like eddy currents. Warnings. It can be arranged that such psi eddy currents make your eyelids twitch. Keep it up, and probability changes to shift the most-likely consequences of the violence. This is like a spinning copper disk getting hot. Then, if you're obstinate about it, you get the equivalent of the copper disk melting. Probability gets so drastically changed that the violent thing you're trying to do becomes something that can't happen. Hm-m-m. ... You can't spin a copper disk in a magnetic field when it melts. You can't commit a murder in a certain kind of psi field when probability goes hog-wild. Any other thing can happen to anybody else—to you, for example—but no violence can happen to the thing or person you're trying to do something violent to. The psi field has melted down ordinary probabilities. The violence you intend has become the most improbable of all conceivable things. You see?"

"I'm beginnin'," said Detective Sergeant Fitzgerald dizzily, "I'm beginnin' to get a toehold on what you mean. I'd hate to have to testify about it in court, but I'm receptive."

"So my special kind of luck," said Brink, "comes from antiviolence psi fields, set up in psi units of suitable material. They don't use up energy any