operating machine—things get messed up. The operating habit is busted to hell. I'm saying that if this wave-type makes crazy surges of current start up—why—if the surges are strong enough they'll bust not only a communicator but a jet-plane. Or a water-spout. Anything! See?"

Lecky blinked and suddenly went pale.

"But," said Howell reasonably, "you said that Betsy handled it. Especially well when linked with other Mahon machines."

"Yeah," said the sergeant.

"I think," observed Graves jerkily, "that you are preparing new machines, without developed—personalities, because you think that if they make this special-type wave they'll be broken."

"Yeah," said the sergeant, again. "The signal Betsy was amplifyin' coulda been as little as a micro-micro-watt. At its frequency an' type, she'd choke it down if it was more. But even a micro-micro-watt bothered Betsy until she got Al and Gus to help. She was fair screamin' for somebody to come help her hold it. But the three of them done all right."

Howell conceded the point.

"That seems sound reasoning."

"But you don't broadcast with a micro-micro-watt. You use a hell of a lot more power than that! The transmitter the guy in the screen said to make was a twenty-kilowatt job. Not too much for a broadcast of sine waves, but a hell of a lot to be turned loose, in waves that have Betsy hollerin' at the power she was handlin'!"

"It might break even the Mahon machines in this installation?" demanded Howell.

"You're gettin' warm," said the sergeant.

Graves said:

"You mean it might break all operating communicators in a very large area?"

"You're gettin' hot," said the sergeant grimly.

Lecky wetted his lips.

"I think," he said very carefully, "that you suspect it is a wave-type which will break any dynamic system, in any sort of object a dynamic system can exist in."

"Yeah," said the sergeant. He waited, looking at Lecky.

"And," said Lecky, "not only operating machines are dynamic systems. Living plants and animals are, too. So are men."

"That's what I'm drivin' at," said Sergeant Bellews.

"So you believe," said Lecky, very pale indeed, "that we have been given the circuit-diagram of a transmitter which will broadcast a wave-type which destroys dynamic systems—life as well as the operation of machines. Persons—in the future or an alien creature in a space-ship, or perhaps even the Compubs—are furnishing us with designs for transmitters of death, to be linked together so that if one fails the others will carry on. And they lure us to destroy ourselves by lying about who they are and what they propose."

"They're lyin'," said the sergeant. "They say they're in the future and they don't know a thing about Mahon units. Else they'd use 'em."

Lecky wetted his lips again.

"And—if they are not in the future, they are trying to get us to destroy ourselves because that would be safer and surer than trying to destroy us by—say—transmitters of death dropped upon us by parachute. Yet if we do not destroy ourselves, they will surely do that."

"If we don't bump ourselves off, it'll be because we got wise," acknowledged the sergeant. "If we get wise, we could bump them off by parachute-transmitter. So they'll beat us to it. They'll have to!"

"Yes," said Lecky. "They'll have to. It has always been said that a death-ray was impossible. This would be a death-broadcast. If we do not broadcast, they will—whoever they are. It is—" He smiled mirthlessly at the magnitude of his understatement. "It is urgent that we do something. What shall we do, Sergeant?"

A squadron of light tanks arrived at Research Installation 83 that afternoon, with a shipment of courier motorcycles. They had been equipped with Mahon units and went to the post to be trained.

The Pentagon was debating the development of a Mahon-modified guided missile, and a drone plane was under construction. But non-military items also arrived for activation and test. Automatic telephone switching systems, it appeared, could be made much simpler if they could be trained to do their work instead of built so they couldn't help it.

Passenger-cars other than jeeps showed promise. It had long been known that most accidents occurred with new cars, and that ancient jalopies were relatively safe even in the hands of juvenile delinquents. It was credible that part of the difference was in the operating habits of the cars.

It appeared that humanity was upon the threshold of a new era, in which the value of personality would reappear among the things taken for granted. Strictly speaking, of course, Mahon machines were not persons. But they reflected the personalities of their owners. It might again seem desirable to be a decent human being if only because machines worked better for them.

But it would be tragic if Mahon machines were used to destroy humankind with themselves! Sergeant Bellews would have raged at the thought of training a Mahon unit to guide an atom bomb. It would have to be—in a fashion—deceived. He even disliked the necessity he faced that afternoon while a courier winged his way to the Pentagon with the top-secret tapes Betsy and Al and Gus had made.

The Rehab Shop was equipped not only to recondition machines but to test them. One item of equipment was a generator of substitute broadcast waves. It could deliver a carrier-wave down to half a micro-micro-watt of any form desired, and up to the power of a nearby transmitter. It was very useful for calibrating communicators. But Sergeant Bellews modified it to allow of variations in type as well as frequency and amplitude.

"I'm betting," he grunted, "that there's different sorts of the wave-type those guys want us to broadcast. Like there's a spectrum of visible light. If we were color-blind and yellow'd bust things, they'd transmit in red that we could see, and they'd tell us to broadcast something in yellow that'd wipe us out. And we wouldn't have sense enough not to broadcast the yellow, because we wouldn't know the difference between it and red until we did broadcast. Then it'd be too late."

Howell watched with tight-clamped jaws. He had committed himself to the authenticity of the broadcasts claiming to be from a future time. Now he was shaken, but only enough to admit the need for tests. Graves sat unnaturally still. Lecky looked at Sergeant Bellews with a peculiarly tranquil expression on his face.

"Only," grunted the sergeant, "it ain't frequency we got to figure, but type. Nobody hardly uses anything but sine waves for communication, but I got to make this gadget turn out a freak wave-type by guess and golly. I got a sort of test for it, though."

He straightened up and connected a cable from the generator to the Mark IV communicator which was a factory twin of Betsy.

"I'm gonna feed this communicator half a micro-micro-watt of stuff like the broadcast—I think," he announced grimly. "I saw the diagrams of the transmitters they want us to make. I'm guessing the broadcast-wave they use is close to it but not exact. Close, because it's bad for machines. Not exact, because they're alive while they use it. I hope I don't hit anything on the nose. Okay?"

Lecky said gently:

"I have never been more frightened. Go ahead!"

Sergeant Bellews depressed a stud. The communicator's screen lighted up instantly. It was receiving the generator's minute output and accepted it as a broadcast. But the signal was unmodulated, so there was no image nor any sound.

The communicator's standby light flickered steadily.

Sergeant Bellews adjusted a knob on the generator. The communicator's standby flicker changed in amplitude. Bellews turned the knob back. He adjusted another control. The standby light wavered crazily.

Graves said nervously:

"I think I see. You are trying to make this communicator react as Betsy did. When it does, you will consider that your