nly to find that the letter has been
forged, presumably by a German.

"Question: Can the same German be the agent in both cases?"

"Bless my arithmetic! how concisely you put it!" exclaimed Mr. Damon.

"It is part of my training, I suppose," remarked the officer. "But it
strikes me that if we find your German spy, Tom, we will find the man
who played the joke on me. And if I do find him--well, I think I shall
know how to deal with him," and General Waller assumed his
characteristic haughty attitude.

"I believe you are right, General," spoke Tom. "Though why any German
would want to prevent my experiments, or even damage my property, and
possibly injure my friends, I cannot understand."

"Nor can I," spoke the officer.

"I am sorry you have had your trouble for nothing," went on Tom. "And,
if you are in this vicinity when I conduct my next test, I shall be
glad to have you come. I will send word by Mr. Damon, and then there
will be no chance of a mistake."

"Thank you, Tom, I shall be glad to come I do not know how long I shall
remain in this vicinity. If I knew where to look for the German I would
make a careful search. As it is, I shall turn this letter over to the
United States Secret Service, and see what its agents can do. And, Tom,
if you are annoyed again, let me know. You are a sort of rival, so to
speak, but, after all, we are both working to serve Uncle Sam. I'll do
my best to protect you."

"Thank you, sir," replied Tom. "On my part, I shall keep a good
lookout. It will be a bold spy who gets near my shop after this. I'm
going to put up my highly-charged protecting electric wires again. We
were just talking about them when you came in. Would you like to look
about here, General?"

"I would, indeed, Tom. Have you made your big gun yet?"

"No, but I am working on the plans. I want first to decide on the kind
of explosive I am to use, so I can make my gun strong enough to stand
it."

"A wise idea. I think there is where I made my mistake. I did not
figure carefully enough on the strength of material. The internal
pressure of the powder I used, as well as the muzzle velocity of my
projectile, were both greater than they should have been. Take a lesson
from my failure. But I am going to start on another gun soon, and--Tom
Swift--I am going to try to beat you!"

"All right, General," answered Tom, genially. "May the best gun win!"

"Bless my powder box!" cried Mr. Damon. "That's the way to talk."