An explosion that shook the ground followed almost instantly. From the bed of the river a geyser of mud and water and rocks spouted up, showering everything for a radius of several yards. The explosion the professor had dreaded had taken place; but, by a miracle, no one was hurt. No doubt the fact that the detonation took place below the river bank accounted for this fact.
But the lecture that Ding-dong received! And he admitted that he deserved it.
“If you ever catch me mo-mo-monkeying with that h-h-high-diddle-diddle g-g-g-gas again you can ber-ber-ber-blow me up with it,” he declared.
“That ‘high-diddle-diddle gas,’ as you call it, is much too precious for that,” said the professor with a laugh he could not restrain, “but I shall adopt other measures.”
The boys had a good opportunity then to see the destructive force stored in one of those innocent-looking cylinders. Peering over the river bank they could see that a great hole had been blown in its bed, and rocks riven and split in every direction.
“It’s as explosive as dynamite,” exclaimed Nat.
“It is, indeed,” said the professor. “The condition of that river bed gives mute evidence of that.”
“Just think what would happen if a spark should ever enter that gas bag of ours,” said Nat, with a slight shudder.
“We wouldn’t be able to think,” said Joe succinctly.
“Come, let us get back to work,” suggested the professor, “roll that gas cylinder closer to the filler tube and we will make the connections.”