frequencies—speed-up and slow-down stuff. They laughed themselves sick! There used to be a tough guy over there,—a staff sergeant, he was—that gave lectures on military morals in a deep bass voice. He was proud of that bull voice of his. He used it frequently. So they taped him, and Al here—" the name plainly referred to the machine—"used to play it back switched up so he sounded like a squeaky girl. That poor guy, he liked to busted a blood-vessel when he heard himself speakin' soprano. He raised hell and they sent Al here to be rehabilitated. But I switched another machine for him and sent it back, instead. Of course, Al don't know what he's doing, but—"

He brought over another device, slightly larger and with a screen.

"Somebody had a bright notion with this one, too," he said. "They figured they'd scramble pictures for secret transmission, like they scramble voice. But they found they hadda have team-trained sets to work, an' they weren't interchangeable. They sent Gus here to be deactivated an' trained again. I kinda hate to do that. Sometimes you got to deactivate a machine, but it's like shooting a dog somebody's taught to steal eggs, who don't know it's wrong."

He bolted the two instruments together. He made connections with flexible cables and tucked the cable out of sight. He plugged in for power and began to make adjustments.

The small scientist asked curiously:

"What are you preparing, Sergeant?"

"These two'll unscramble that broadcast," said Sergeant Bellews, with tranquil confidence. "Al's learned how to make a tape and switch frequencies expert. Gus, here, he's a unscrambler that can make any kinda scanning pattern. Together they'll have a party doing what they're special trained for. We'll hook 'em to Betsy's training-terminals."

He regarded the two machines warmly. Connected, now, their standby lights flickered at a new tempo. They synchronized, and broke synchrony, and went back into elaborate, not-quite-resolvable patterns which were somehow increasingly integrated as seconds went by.

"Those lights look kinda nice, don't they?" asked the sergeant admiringly. "Makes you think of a coupla dogs gettin' acquainted when they're goin' out on a job of hunting or something."

But Lecky said abruptly, in amazement:

"But, Sergeant! In the Pentagon it takes days to unscramble a received broadcast such as Betsy receives! It requires experts—"

"Huh!" said Sergeant Bellews. He picked up the two machines. "Don't get me started about the kinda guys that wangle headquarters-company jobs! They got a special talent for fallin' soft. But they haven't necessarily got anything else!"

Lecky followed Sergeant Bellews as the sergeant picked up his new combination of devices and headed out of the Rehab Shop. Outside, in the sunshine, there were roarings to be heard. Lecky looked up. A formation of jets swam into view against the sky. A tiny speck, trailing a monstrous plume of smoke, shot upward from the jet-field. The formation tightened.

The ascending jet jiggled as if in pure exuberance as it swooped upward—but the jiggle was beautifully designed to throw standard automatic gunsights off.

A plane peeled off from the formation and dived at the ascending ship. There was a curious alteration in the thunder of motors. The rate-of-rise of the climbing jet dwindled almost to zero. Sparks shot out before it. They made a cone the diving ship could not avoid. It sped through them and then went as if disappointedly to a lower level. It stood by to watch the rest of the dog-fight.

"Nice!" said Sergeant Bellews appreciatively. "That's a Mahon jet all by itself, training against regular ships. They have to let it shoot star-bullets in training, or it'd get hot and bothered in a real fight when its guns went off."

The lower jet streaked skyward once more. Sparks sped from the formation. They flared through emptiness where the Mahon jet had been but now was not. It scuttled abruptly to one side as concerted streams of sparks converged. They missed. It darted into zestful, exuberant maneuverings, remarkably like a dog dashing madly here and there in pure high spirits. The formation of planes attacked it resolutely.

Suddenly the lone jet plunged into the midst of the formation, there were coruscations of little shooting stars, and one-two-three planes disgustedly descended to lower levels as out of action. Then the single ship shot upward, seemed eagerly to shake itself, plunged back—and the last ships tried wildly to escape, but each in turn was technically shot down.

The Mahon jet headed back for its own tiny airfield. Somehow, it looked as if, had it been a dog, it would be wagging its tail and panting happily.

"That one ship," said Lecky blankly, "it defeated the rest?"

"It's got a lot of experience," said the sergeant. "You can't beat experience."

He led the way into Communications Center. In the room where Betsy stood, Howell and Graves had been drawing diagrams at each other to the point of obstinacy.

"But don't you see?" insisted Howell angrily. "There can be no source other than a future time! You can't send short waves through three-dimensional space to a given spot and not have them interceptible between. Anyhow, the Compubs wouldn't work it this way! They wouldn't put us on guard! And an extra-terrestrial wouldn't pretend to be a human if he honestly wanted to warn us of danger! He'd tell us the truth! Physically and logically it's impossible for it to be anything but what it claims to be!"

Graves said doggedly:

"But a broadcast originating in the future is impossible!"

"Nothing," snapped Howell, "that a man can imagine is impossible!"

"Then imagine for me," said Graves, "that in 2180 they read in the history books about a terrible danger to the human race back in 1972, which was averted by a warning they sent us. Then, from their history-books, which we wrote for them, they learn how to make a transmitter to broadcast back to us. Then they tell us how to make a transmitter to broadcast ahead to them. They don't invent the transmitter. We tell them how to make it—via a history book. We don't invent it. They tell us—from the history book. Now imagine for me how that transmitter got invented!"

"You're quibbling," snapped Howell. "You're refusing to face a fact because you can't explain it. I say face the fact and then ask for an explanation!"

"Why not ask them," said Graves, "how to make a round square or a five-sided triangle?"

Sergeant Bellews pushed to a spot near Betsy. He put down his now-linked Mahon machines and began to move away some of the recording apparatus focused on Betsy.

"Hold on there!" said Howell in alarm. "Those are recorders!"

"We'll let 'em record direct," said the sergeant.

Lecky spoke feverishly in support of Bellews. But what he said was, in effect, a still-marveling description of the possibilities of Mahon-modified machines. They were, he said with ardent enthusiasm, the next step in the historic process by which successively greater portions of the cosmos enter into a symbiotic relationship with man. Domestic animals entered into such a partnership aeons ago. Certain plants—wheat and the like—even became unable to exist without human attention. And machines were wrought by man and for a long time served him reluctantly. Pre-Mahon machines were tamed, not domestic. They wore themselves out and destroyed themselves by accidents. But now there were machines which could enter into a truly symbiotic relationship with humanity.

"What," demanded Howell, "what in hell are you talking about?"

Lecky checked himself. He smiled abashedly:

"I think," he said humbly, "that I speak of the high destiny of mankind. But the part that applies at the moment is that Sergeant Bellews must not be interfered with."

He turned and ardently assisted Sergeant Bellews in making room for the just-brought