“Wait until I get my revolver,” whispered Jerry. “We’ll soon see if it’s a ghost or not.”

“Don’t fire,” cautioned the professor. “It may be some one trying to scare us, but we have no right to fire at any one.”

“I’ll give ’em a warning, at any rate,” said the lad. He went to the opening and called down:

“Tell us who you are or I’ll shoot, do you hear?”

A groan and the clanking of chains was the only answer. This was followed by a violent agitation and shaking of the ladder.

“Bang!” went Jerry’s revolver. He had fired into the air.

Succeeding the report there was a silence. This was broken by a further clanking of chains. Then came a crash, and when the echo of this died away the sound of feet running away could be heard.

“Pretty solid footsteps for a ghost,” commented Ned.

“Look! Look!” cried Bob, pointing out of the window.