"Bless my armor plate!" gasped Mr. Damon. "What attacking ship against the Panama Canal could float after a shot like that."
"Not one," declared Tom; "especially after I put a bursting charge into the projectile. We'll try that next."
By means of compressed air the gases and some particles of the unexploded powder were blown out of the big cannon. Then it was loaded again, the projectile this time carrying a bursting charge of another explosive that would be set off by concussion.
Once more they retired to the bombproof, and again the great gun was fired. Once more the ground shook, and they were nearly deafened by the shock.
Then, as they looked toward the distant hillside, they saw a shower of earth and great rocks rise up. It was like a sand geyser. Then, when this settled back again, there was left a gaping hole in the side of the mountain.
"That does the business!" cried Tom. "My cannon is a success!"
The last shot did not go quite as far as the first, but it was because a different kind of projectile was used. Tom was perfectly satisfied, however. Several more trials were given the gun, and each one confirmed the young inventor in his belief that he had made a wonderful weapon.
"If that doesn't fortify the Panama Canal nothing will," declared Ned.
"Well, I hope I can convince Uncle Sam of that," spoke Tom, simply.
The muzzle velocity and the pressure were equal to Tom's highest hopes. He knew, now, that he had hit on just the right mixture of powder, and that his gun was correctly proportioned. It showed not the slightest strain.