He turned back to me and demanded, "Have you any change in your pocket?"

I reached in and hauled out a handful. He glanced at it and selected two five-dollar pieces, mint new, the pretty green plastic hexagonals issued just that year. I could have wished that he had picked half fives, as I was running low.

"Do you have a knife?"

"Yes, sir."

"Scratch your initials on each of them."

I did so. He then had me place them side by side on the stage. "Note the exact time. I have set the displacement for exactly one week, plus or minus six seconds."

I looked at my watch. Dr. Twitchell said, "Five...our three... two... one... now."

I looked up from my watch. The coins were gone. I didn't have to pretend that my eyes bugged out. Chuck had told me about a similar demonstration-but seeing it was another matter.

Dr. Twitchell said briskly, "We will return here one week from tonight and wait for one of them to reappear. As for the other one-you saw both of them on the stage? You placed them there yourself?"

"Yes, sir."

"Where was I?"

"At the control board, sir." He had been a good fifteen feet from the nearest part of the cage around the stage and had not approached it since.

"Very well. Come here." I did so and he reached into a pocket. "Here's one of your bits. You'll get the other back a week from now." He handed me a green five-dollar coin; it had my initials on it.

I did not say anything because I can't talk very well with my jaws sagging loosely. He went on, "Your remarks last week disturbed me. So I visited this place on Wednesday, something I have not done for-oh, more than a year. I found this coin on the stage, so I knew that it had been... would be... using the equipment again. It took me until tonight to decide to demonstrate it to you."

I looked at the coin and felt it. "This was in your pocket when we came here tonight?"

"Certainly."

"But how could it be both in your pocket and my pocket at the same time?"

"Good Lord, man, have you no eyes to see with? No brain to reason with? Can't you absorb a simple fact simply because it lies outside your dull existence? You fetched it here in your pocket tonight-and we kicked into last week. You saw. A few days ago I found it here. I placed it in my pocket. I fetched it here tonight. The same coin... or, to be precise, a later segment of its space-time structure, a week more worn, a week more dulled-but what the canaille would call the `same' coin. Although no more identical in fact than is a baby identical with the man the baby grows into. Older."

I looked at it. "Doctor ... push me back in time by a week."

He stared angrily. "Out of the question!"

"Why not? Won't it work with people?"

"Eh? Certainly it will work with people."

"Then why not do it? I'm not afraid. And think what a wonderful thing it would be for the book... if I could testify of my own knowledge that the Twitchell time displacement works."

"You can report it of your own knowledge. You just saw it."

"Yes," I admitted slowly, "but I won't be believed. That business with the coins... I saw it and I believe it. But anyone simply reading an account of it would conclude that I was gullible, that you had hoaxed me with some simple legerdemain."

"Damn it, sir!"

"That's what they would say. They wouldn't be able to believe that I actually had seen what I reported. But if you were to ship me back just a week, then I could report of my own knowledge-"

"Sit down. Listen to me." He sat down, but there was no place for me to sit, although he did not seem aware of it. "I have experimented with human beings long ago. And for that reason I resolved never to do it again."

"Why? Did it kill them?"

"What? Don't talk nonsense." He looked at me sharply, added, "You are not to put this in the book."

"As you say, sir."

"Some minor experiments showed that living subjects could make temporal displacements without harm. I had confided in a colleague, a young fellow who taught drawing and other matters in the school of architecture. Really more of an engineer than a scientist, but I liked him; his mind was alive. This young chap-it can't hurt to tell you his name: Leonard Vincent-was wild to try it... really try it; he wanted to undergo major displacement, five hundred years. I was weak. I let him."

"Then what happened?"

"How should I know? Five hundred years, man! I'll never live to find out."

"But you think he's five hundred years in the future?"

"Or the past. He might have wound up in the fifteenth century. Or the twenty-fifth. The chances are precisely even. There's an indeterminacy-symmetrical equations. I've sometimes thought no, just a chance similarity in names."

I didn't ask what he meant by this because I suddenly saw the similarity, too, and my hair stood on end. Then I pushed it out of my mind; I had other problems. Besides, chance similarity was all it could be-a man could not get from Colorado to Italy, not in the fifteenth century.

"But I resolved not to be tempted again. It wasn't science, it added nothing to the data, If he was displaced forward, well and good. But if he was displaced backward... then possibly I sent my friend to be killed by savages. Or eaten by wild animals."

Or even possibly, I thought, to become a "Great White God." I kept the thought to myself. "But you needn't use so long a displacement with me."

"Let's say no more about it, if you please, sir."

"As you wish, Doctor." But I couldn't drop it. "Uh, may I make a suggestion?"

"Eh? Speak up."

"We could get almost the same result by a rehearsal."

"What do you mean?"

"A complete dry run, with everything done just exactly as if you were intending to displace a living subject-I'll act out that part. We'll do everything precisely as if you meant to displace me, right up to the point where you would push that button. Then I'll understand the procedure... which I don't quite, as yet."

He grumbled a little but he really wanted to show off his toy. He weighed me and set aside metal weights just equal to my hundred and seventy pounds. "These are the same scales I used with poor Vincent."

Between us we placed them on one side of the stage. "What temporal setting shall we make?" he asked. "This is your show."

"Uh, you said that it could be set accurately?"

"I said so, sir. Do you doubt it?"

"Oh no, no! Well, let's see, this is the twenty-fourth of May-suppose we... how about, uh, say thirty-one years, three weeks, one day, seven hours, thirteen minutes, and twenty-five seconds?"

"A poor jest, sir. When I said `accurate' I meant `accurate to better than one part in one hundred thousand.' I have had no opportunity to calibrate to one part in nine hundred million."

"Oh. You see, Doctor, how important an exact rehearsal is to me, since I know so little about it. Uh, suppose we call it thirty-one years and three weeks. Or is that still too finicky?"

"Not at all. The maximum error should not exceed two hours." He made his adjustments. "You can take your place on the stage."

"Is that all?"

"Yes. All but the power. I could not actually make this displacement with the line voltage I used on those coins. But since we aren't actually going to do it, that doesn't matter."

I looked disappointed and was. "Then you don't actually have what is necessary to produce such a displacement? You were speaking theoretically?"

"Confound it, sir, I was not speaking theoretically."

"But if you don't have the power... ?"

"I can get the power if you insist. Wait." He went to a corner of the lab and picked up a phone. It must have been installed when the lab was new; I hadn't seen one like it since I was awakened. There followed a brisk conversation with the night superintendent of the university's powerhouse. Dr. Twitchell was not dependent on profanity; he could avoid it entirely and be more biting than most real artists can be when using plainer words. "I am not in the least interested in your opinions, my man. Read your instructions. I have full facilities whenever I wish them. Or can you read? Shall we meet with the president at ten tomorrow morning and have him read them to you? Oh? So you can read? Can you write as well? Or have we exhausted your talents? Then write this down: Emergency full power across the bus bars of the Thornton Memorial Laboratory in exactly eight minutes. Repeat that back."