"Oh, it will probably be harmlessly conducted down on the heavy wires," said Mr. Parker. "We are in no danger, at present, though ultimately I expect to see the whole mountain shattered by a lightning bolt."
"Cheerful prospect," murmured Tom.
There was a terrific crash outside. The rocky floor of the cave trembled.
"Here she comes!" cried Folwell. "Get back, everybody! I'm going to throw over the switch now!"
The men retreated well away from the steel box. Folwell threw over the lever—the same one Mr. Jenks remembered pulling. Then the man ran to the electric switch on the wall, and snapped that into place, establishing a connection.
There was a moment's pause, as Folwell ran to join the others in their place of safety. Then from without there came a most nerve-racking and terrifying crash. It seemed as if the very mountain would be rent into fragments.
Watching with eager eyes, the adventurers saw sparks flash from the steel box. Instantly it became red hot, and then glowed white and incandescent. It was almost at the melting point.
Then came comparative quiet, as the echoes
