steel workers, who had helped in casting many big guns. "No cannon ever made can equal it. You win, Tom Swift!"
"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 bomb-proof, 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 pro-
