sniffed contemptuously.

"That's nothing," he retorted. "I've got it figured out already. Only it'll take a special lens, not just a concave one. Because now it doesn't just reverse letters like a mirror; it transposes them—"

"All right, all right!" The professor threw up his hands in despair. "This is one time you've invented something worth while, and you seem to have some kind of notion of how it works, for a change."

"How you talk!" Henry was suddenly cocky. He sneered. "I always know how my inventions work—"

His gaunt friend glowered.

"I was afraid of this," he grunted. "Give you half a compliment and there's no living with you." Then: "However, I won't waste time and energy bringing you down to earth right now. The main thing is, get your notes together. I want you to show them to Major Coggleston tonight; I think maybe the army can use this invention of yours."

And, as Henry again raised the glasses in the direction of the nudist camp:

"But get rid of those glasses for now. I don't want to catch you ogling blonde beauties, or any other kind. Those people in that camp put up that fence because they wanted privacy. So put those binoculars away right now. Do you understand?"

"Oh, all right," fretted Henry. "I'll get rid of them."

Dinner was a thing of the past, and Major Coggleston, Professor Paulsen and Henry were settled comfortably on the front porch, enjoying the quiet of the summer evening.

"If these glasses of yours work as well as you say they do, the Army certainly can use them," commented the major thoughtfully. "Such an invention would completely revolutionize espionage and its counter-measures. Nothing would be safe! Why, a spy could stand half-a-mile from the laboratory I'm supposed to be protecting, look through the walls to the records room, and steal the formulae for our latest explosives right from under our noses, with none of us the wiser."

"Yes." The professor nodded. "I can see how much it would mean. That's why I had you over tonight—wanted you to have a chance to investigate." A pause. "By the way, how's the work coming at the laboratory?"

"Better than we'd hoped for, Joe. We've got a young fellow in charge who's a genius on explosives." The major hesitated for a moment, then continued: "Confidentially, I understand he's just developed a new powder that makes TNT look like something to use for loading firecrackers. It's the greatest thing in years. The Nazis and Japs would give their eye-teeth for it. It's simpler to make than gunpowder, even—"

Brrrnng!

"I'll answer," said Henry. He skittered inside to the telephone.

A minute later he was back.

"It's for you, Major Coggleston."

The officer hurried to answer. When he returned, his face was tense with worry.

"Something's wrong!" he rapped. "It looks like the Nazis have made a play for that formula already! I've got to get right back to the laboratory!"

Henry and the professor still were excitedly discussing this news when, half an hour later, the 'phone rang again. This time the tall scientist answered. He returned to the porch frowning.

"That was Coggleston," he reported. "Apparently the spy didn't get the formula, but he made a clean getaway, and he killed a sentry to do it."

"Oh, that's terrible!" Henry was afire with indignation. "Of all things! Killing a sentry—"

"Yes." The professor nodded. "The trouble is, Coggleston says they don't have much to go on. No description, except that he was big and had red hair—"

"Red hair!"

"Yes. Red hair." The savant eyed Henry suspiciously. "Why does that surprise you so?"

"Why ... er ... oh, it doesn't. I mean—"

"What do you mean?"

"Really, Joseph, it's nothing." The little man squirmed nervously, his goatee hanging guiltily to one side. "I'm not surprised at all. Really I'm not!"

"Oh, you're not, aren't you?" Professor Paulsen started across the room with grim