t I have a few hours to spare before the
doctor can get here, I'm going to make an examination."

"Bless my penwiper, but I'll help you."

Tom went into the house, to inquire of Mrs. Baggert, for probably the
tenth time that morning, how his father was doing. Mr. Swift was still
in a semi-conscious condition, but he recognized Tom, when the youth
stood at his bedside.

"Don't worry about me, son," said the brave old inventor, as he took
Tom's hand. "I'll be all right. Go ahead and get ready for the race. I
want you to win!"

Tears came into Tom's eyes. Would his father be well enough to allow
him to take part in the big event? He feared not.

By daylight it was seen that quite a hole had been burned in the
aeroplane shed. Tom and Mr. Damon, accompanied by Mr. Jackson, walked
through the place.

"And you say the fire broke out right after you had seen the mysterious
airship hovering over the house?" asked the eccentric man.

"Well, not exactly after," answered Tom, "but within an hour or so. Why
do you ask?"

But Mr. Damon did not answer. Something on the floor of the shed, amid
a pile of blackened and charred pieces of wood, attracted his
attention. He stooped over and picked it up.

"Is this yours?" he asked Tom.

"No. What is it?"

The object looked like a small iron ball, with a tube about half an
inch in diameter projecting slightly from it. Tom took it'.

"Why, it looks like an infernal machine or a dynamite bomb," he said.
"I wonder where it came from? Guess I'd better drop it in a pail of
water. Maybe Eradicate found it and brought it here. I never saw it
before. Mr. Jackson, please hand me that pail of water. We'll soak this
bomb."

"There is no need," said Mr. Damon, quietly. "It is harmless now. It
has done its work. It was that which set fire to your shed, and which
caused the stifling fumes."

"That?" cried Tom.

"Yes. This ball is hollow, and was filled with a chemical. It was
dropped on the roof, and, after a certain time, the plug in the tube
was eaten through, the chemicals ran out, set the roof ablaze, and,
dripping down inside spread the choking odors that nearly prevented you
from getting out your aeroplane."

"Are you sure of this?" asked the young inventor.

"Positive. I read about these bombs recently. A German invented them to
be used in attacking a besieged city in case of war."

"But how did this one get on my shed roof?" asked Tom.

"It was dropped there by the myste