After securing Ned's searchlight which, owing to its waterproof covering, was not damaged, the boys proceeded more cautiously.
In a short time they found the passage partly blocked by huge masses of stone, evidently the remains of masonry dislodged by the invaders' shells. A faint odor of powder clung to the place.
"Here's where the opening to the old portion of the castle was located, or I'm no good guesser!" ventured Jimmie.
Although careful search was made for an opening none was discovered, and the party continued along the tunnel-like place. Directly Ned paused and held out a warning hand, stopping the advance.
"I heard a noise," he explained, "and could not make out what it might be. Can any of you tell what that noise is?"
Listening carefully, the boys distinctly heard a whirring rumble, but could not determine its cause nor what it indicated.
"Oh, I've got it!" gleefully announced Jimmie directly. "The Duke de Wun Lung had nothing else to do, so he installed his own power plant! This stream of water comes from a spring in the hill back there somewhere, and the old chap just led it along here. It runs through a water wheel, and the waste water runs out a nice little hole in the cellar wall! Pity he didn't put in a ram and have water in the house!"
"I believe you're right, Jimmie!" agreed Ned. "Let's see!"
Following the passage a short distance, the boys discovered that Jimmie's guess had been correct. A complete apparatus was found, operated by the power of the stream flowing through the tunnel.