But, it must be confessed, after Tom and Ned had spent the rest of that
day in and about the burned shed, they were little wiser than when they
started. They found the place where the fire bomb had evidently been
placed, right inside the main entrance to the shed. Tom knew it had
been there because there were peculiar marks on the charred wood, and a
certain queer smell of chemicals that confirmed his belief.

"They put the bomb there to prevent anyone going in at the first alarm
and saving anything," Tom said. "They didn't count on the roof burning
through first, giving me a chance to use the sand. I made the roof of
the red shed flimsy just on that account, so the force of the explosion
if one ever came, would be mostly upward. You know the expanding gases,
caused by an explosion or by rapid 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