med
Ned Newton, with a laugh.

This was several days after our friends had returned from the
disastrous gun test at Sandy Hook. Tom had at once gotten to work on
the problem that confronted him--a problem of his own making--to build
a giant cannon that would make the longest shots on record. And he had
first turned his attention to the powder, or explosive, to be used.

"For," he said, "there is no use having a big gun unless you can fire
it. And the gun I am planning will need something more powerful in the
powder line than any I've ever heard of."

"Stronger than the kind General Waller used?" inquired Ned.

"Yes, but I'll make my cannon correspondingly stronger, too, so there
will be no danger."

"Bless my shoe buttons!" exclaimed Mr. Damon. "You boys must have had
your nerve with you to stay around Sandy Hook after that gun went up in
the air."

"Oh, the danger was all over soon after it began," spoke Tom, with a
smile. "But now I'm going to test some of this powder. If you want to
run away, Mr. Damon, I'll have Koku take you up in one of the airships,
and you'll certainly be safe a mile or so in the air," for Tom had
instructed his giant servant how to run one of the simpler biplanes.

"No--no, Tom, I'll stick!" exclaimed the eccentric man. "I'll not
promise not to hide behind the fence, or something like that, though,
Tom; but I'll stick."

"So will I," added Ned. "How are you going to make the test, Tom?"

"I'll tell you in a minute. I want to do a little figuring first."

Tom had, before going to Sandy Hook, made some experiments in powder
manufacturing, but they had not been very satisfactory. He had not been
able to get power enough. On his return he had undertaken rather a
daring innovation. He had mingled two varieties of powder, and the
resulting combination would, he hoped, prove just what he wanted.

The powder was in gelatin form, being made with nitro-glycerine as a
base. It looked, as Mr. Damon had said, like a bunch of excelsior, only
it was yellow instead of white, and it felt not unlike pieces of dry
macaroni.

"I have shredded the powder in this manner," Tom explained, "so that it
will explode more evenly and quickly. I want it to burn as nearly
instantaneously as possible, and I think it will in this form."

"But how are you going to tell how powerful it is unless you fire it in
a cannon?" asked Ned. "And you haven't even started your big gun yet."

"Oh, I'll show you," declared T