"Oh, don't get nervous," laughed Tom. "It can't hurt you now.
But what does that smell like?"

Ned sniffed, sniffed again, thought for a moment, and then
sniffed a third time.

"Why," he said slowly, "I don't just know the name of it, but
it's that funny stuff you mix up sometimes to put in the oxygen
tanks when we go up in the rarefied atmosphere in the balloon or
airship."

"Manganese and potash," spoke Tom. "That and two or three other
things that form a chemical combination which goes off by itself
of spontaneous combustion after a certain time. Only the person
who put this bomb together didn't get the chemical mixture just
right, and it went off ahead of time; for which we have to be
duly thankful."

"Do you really think that, Tom?" cried Ned.

"I'm positive of it," was the quiet answer.

"Why--why--that would mean some one tried to set fire to the
red shed, Tom!"

"They not only tried it, but did it," responded Tom, more
coolly than seemed natural under the circumstances. "Only for the
fact that the mixture went off before it was intended to, and
found us all alert and ready--well, I don't like to think what
might have happened," and Tom cast a look about at his group of