combustion, always do just as electricity does, seek the shortest and easiest route. In this case I made the roof the easiest route."

"A lucky provision," observed Ned.

That night Tom had to confess himself beaten, as far as finding clues was concerned. The empty fire bomb was the only one, and that seemed valueless.

Close questioning of the workmen failed to disclose anything. Tom was particularly anxious to discover if any mysterious strangers had been seen about the works. There was a strict rule about admitting them to the plant, however, and it could not be learned that this had been violated.

"Well, we'll just have to lay that aside for a while," Tom said the next day, when Ned again came to pay a visit. "Now, what do you say to tackling, with me, that recoil problem on the aerial warship?"

"I'm ready, if you are," Ned agreed, "though I know about as much of those things as a snake does about dancing. But I'm game."

The two friends walked out toward the shed where Tom's new craft was housed. As yet Ned had not seen it. On the way they saw Eradicate walking along, talking to himself, as he often did.

"I wonder what he has on his mind," remarked Ned musingly.

"Something does seem to be worrying him," agreed Tom.

As they neared the colored man, they could hear him saying:

"He suah did hab nerve, dat's what he did! De idea ob askin' me all dem questions, an' den wantin' t' know if I'd sell him!"

"What's that, Eradicate?" asked Tom.

"Oh, it's a man I met when I were comin' back from de ash dump," Eradicate explained. One of the colored man's duties was to cart ashes away from Tom's various shops, and dump them in a certain swampy lot. With an old ramshackle cart, and his mule, Boomerang, Eradicate did this task to perfection.

"A man—what sort of a man?" asked Tom, always ready to be suspicious of anything unusual.

"He were a queer man," went on the aged colored helper. "First he stopped me an' asted me fo' a ride. He was a dressed-up gen'man, too, an' I were suah s'prised at him wantin' t' set in mah ole ash cart," said Eradicate. "But I done was polite t' him, an' fixed a blanket so's he wouldn't git too dirty. Den he asted me ef I didn't wuk fo' yo', Massa Tom, an' of course I says as how I did. Den he asted me about de fire, an' how much damage it done, an' how we put it out. An' he end up by sayin' he'd laik t' buy mah mule, Boomerang, an' he wants t' come heah dis arternoon an' talk t' me about it."

"He does, eh?" cried Tom. "What sort of a man was he, Rad?"

"Well, a gen'man sort ob man, Massa Tom. Stranger t' me. I nebber seed him afo'. He suah was monstrous polite t' ole black Eradicate, an' he gib me a half-dollar, too, jest fo' a little ride. But I aint' gwine t' sell Boomerang, no indeedy, I ain't!" and Eradicate shook his gray, kinky head decidedly.

"Ned, there may be something in this!" said Tom, in an excited whisper to his chum. "I don't like the idea of a mysterious stranger questioning Eradicate!"

CHAPTER VI

THE AERIAL WARSHIP

Ned Newton looked at Tom questioningly. Then he glanced at the unsuspicious colored man, who was industriously polishing the half-dollar the mysterious stranger had given him.

"Rad, just exactly what sort of a man was this one you speak of?" asked Tom.

"Why, he were a gen'man—"

"Yes, I know that much. You've said it before. But was he an Englishman, an American—or—"

Tom paused and waited for an answer.

"I think he were a Frenchman," spoke Eradicate. "I done didn't see him eat no frogs' laigs, but he smoked a cigarette dat had a funny smell, and he suah was monstrous polite. He suah was a Frenchman. I think."

Tom and Ned laughed at Eradicate's description of the man, but Tom's face was soon grave again.

"Tell us more about him, Rad," he suggested. "Did he seem especially interested in the fire?"

"No, sah, Massa Tom, he seemed laik he was more special interested in mah mule, Boomerang. He done asted how long I had him, an' how much I wanted fo' him, an' how old he was."

"But every once in a while he put in some question about the fire, or about our shops, didn't he, Rad?" Tom wanted to know.

The colored man scratched his kinky head, and glanced with a queer look at Tom.

"How yo' all done guess dat?" he asked.

"Answer my question," insisted Tom.

"Yes, sah, he done did ask about yo', and de wuks, ebery now and den," Rad confessed. "But how yo' all knowed dat, Massa Tom, when I were a-tellin' yo' all about him astin' fo' mah mule, done gets me—dat's what it suah does."

"Never mind, Rad. He asked questions about the plant, that's all I want to know. But you didn't tell him much, did you?"

Eradicate looked reproachfully at his master.

"Yo' all done knows me bettah dan dat, Massa Tom," the old colored man said. "Yo' all know yo' done gib orders fo' nobody t' talk about yo' projections."

"Yes, I know I gave those orders," Tom said, with a smile, "but I want to make sure that they have been followed."

"Well, I done follered 'em, Massa Tom."

"Then you didn't tell this queer stranger, Frenchman, or whatever he is, much about my place?"

"I didn't tell him nuffin', sah. I done frowed dust in his eyes."

Ned uttered an exclamation of surprise.

"Eradicate is speaking figuratively," Tom said, with a laugh.

"Dat's what I means," the colored man went on. "I done fooled him. When he asted me about de fire I said it didn't do no damage at all—in fack dat we'd rather hab de fire dan not hab it, 'case it done gib us a chance t' practice our hose drill."

"That's good," laughed Tom. "What else?"

"Well, he done sort ob hinted t' me ef we all knowed how de fire done start. I says as how we did, dat we done start it ourse'ves fo' practice, an dat we done expected it all along, an' were ready fo' it. Course I knows dat were a sort of fairy story, Massa Tom, but den dat cigarette-smokin' Frenchman didn't hab no right t' asted me so many questions, did he?"

"No, indeed, Rad. And I'm glad you didn't give him straight answers. So he's coming here later on, is he?"

"T' see ef I wants t' sell mah mule, Boomerang, yais, sah. I sort ob thought maybe you'd want t' hab a look at dat man, so I tole him t' come on. Course I doan't want t' sell Boomerang, but ef he was t' offer me a big lot ob money fo' him I'd take it."

"Of course," Tom answered. "Very well, Rad. You may go on now, and don't say anything to anyone about what you have told me."

"I won't, Massa Tom," promised the colored man, as he went off muttering to himself.

"Well, what do you make of it, Tom?" asked Ned of his chum, as they walked on toward the shed of the new, big aerial warship.

"I don't know just what to think, Ned. Of course things like this have happened before—persons trying to worm secrets out of Eradicate, or some of the other men."

"They never succeeded in getting much, I'm glad to say, but it always keeps me worried for fear something will happen," Tom concluded.

"But about this Frenchman?"

"Well, he must be a new one. And, now I come to think of it, I did hear some of the men speaking about a foreigner—a stranger—being around town last week. It was just a casual reference, and I paid little attention to it. Now it looks as though there might be something in it."

"Do you think he'll come to bargain with Eradicate about the mule?" Ned asked.

"Hardly. That was only talk to make Eradicate unsuspicious. The stranger, whoever he was, sized Rad up partly right. I surmised, when Rad said he asked a lot of questions about the mule, that was only to divert suspicion, and that he'd come back to the subject of the fire every chance he got."

"And you were right."

"Yes, so it seems. But I don't believe the fellow will come around here. It would be too