but the
trouble is that it's only a theory. Wait a few seconds."

Anxiously they lingered, the echoes of the blast still in their ears,
and a peculiar smell in their nostrils.

"But there's no smoke," said Mr. Damon. "Bless my spyglass! I always
thought there was smoke at an explosion."

"This is a sort of smokeless powder," explained Tom. "It throws off a
slight vapor when it is ignited, but not much. I guess it's safe to go
out now. Come on!"

He dropped the pushbutton connected with the igniting battery, and,
followed by the others, raced to the scene of the experiment. A curious
sight met their eyes.

A great hole had been torn in the hillside, and another where the
improvised gun had stood. The gun itself seemed to have disappeared.

"Why--why--where is it?" asked Ned.

"Burst to pieces I guess," replied Tom. "I was afraid that charge was a
bit too heavy."

"No, here it is!" shouted Mr. Damon, circling off to one side. "It's
been torn from the carriage, and partly buried in the ground," and he
indicated a third excavation in the earth.

It was as he had said. The terrific blast had sheared the gun from its
temporary carriage, thrown it into the air, and it had come down to
bury itself in the soft ground. The carriage had torn loose from the
concrete base, and was tossed off in another direction.

"Is the gun shattered?" asked Tom, anxious to know how the weapon had
fared. It was, in a sense, a sort of small model of the giant cannon he
intended to have cast.

"The breech is cracked a little," answered Mr. Damon, who was examining
it; "but otherwise it doesn't seem to be much damaged."

"Good," cried Tom. "Another steel jacket will remedy that defect. I
guess I'm on the right road at last. But now to see what became of that
armor plate."

"Dinner plate not here," spoke Koku, who could not understand how there
could be two kind of plates in the world. "Dinner plate gone, but big
hole here, and he indicated one in the side of the hill.

"I expect that is where the armor plate is," said Tom, trying not to
laugh at the mistake of his giant servant. "Take a look in there, Koku,
and, if you can get hold of it, pull it out for us. I'm afraid the
piece of nickel-steel armor proved too much for my projectile. But
we'll have a look."

Koku disappeared into the miniature cave that had been torn in the side
of the bill. It was barely large enough to allow him to go in. But Tom
knew none other of them cou