“No doubt he stole it from someone who is using it for stumping, or some such work as that.  He couldn’t buy it,” said Tom.

“But look at this fuse,” Jack cried.  “It looks as if it had been lighted.  Sure as you’re a foot high it has been lighted.”

“Why didn’t the stuff go off then?” queried Tom.

“I don’t know,” Jack admitted.  “I’m going to pull the end of the burned fuse out of this stick and see what’s the matter.”

Suiting the action to the word, Jack slowly extracted the end of the fuse from the stick of gelatine in which it had been thrust.

“Ha, Ha,” he laughed with a motion as if to slap his thigh.  Startled, he caught himself in time.  The laughter died away.

“What’s the matter, Jack?” inquired Frank.

“I almost dropped one of the sticks,” replied Jack.

“Well, what of it?” innocently Tom suggested.

“Nothing of it,” Jack gruffly responded.  “At least, I might say nothing of the Fortuna and her crew if I had dropped one of the sticks.  They’re only about an inch in diameter and seven or eight inches long, but one of them is enough to blow this vessel into chunks and the six would have blown her to little pieces.”

“But why would dropping it to the floor have done damage?” persisted Tom.  “I thought it had to have fire to explode it.”

“That’s where you’re wrong,” Jack explained.  “Most people have the same idea.  Evidently that was also the idea of the villain who planted this stuff here, for he neglected to put a cap on his fuse.”

“What’s a cap?” Tom eagerly asked.  “I don’t know about this.”

“I couldn’t help but notice it,” Jack scorned.  “Well, it’s just this way—­You see, dynamite will burn without exploding.  A very little jar, however, sometimes is sufficient to set it going and explode it.  When setting off a charge, a cap containing some fulminate of mercury is put over the end of the fuse.  That stuff will explode from fire.  When the fuse burns down to the cap, the cap explodes and the jar of its explosion sets off the dynamite.  See?”

“Thanks,” gratefully replied Tom.  “Now I’m enlightened.  Then the reason the Fortuna is still here is because the guy forgot to put his cap on his fuse?  Am I now correct?”

“Right you are, Tom,” answered Jack.  “Are there any further questions?  If not, the class in explosives is dismissed.”

“One more, Professor, if you please.”  Frank had the floor.  “What shall we do with the stuff?  We don’t want to keep it aboard.”

“That’s a problem,” Jack announced.  “We can’t merely throw it overboard; nor we can’t leave it in a fence corner.  I’ll confess I’m puzzled to know how we shall get rid of it.”

“Let’s leave it until morning,” Tom suggested.  “Just now I’m so worn out I can’t think.  I wish we had Wyckoff here, I’d put it in his pockets and then climb a telegraph pole with him and throw him down good and hard.  When he landed it would explode and he’d get his.”