“Mr. Starr,” said Harry Ford, “it seems to me that stone was thrown, thrown as by the hand of man!”

“Thrown!” exclaimed James Starr. “What do you mean, lad?”

“Nothing, nothing, Mr. Starr,” replied Harry evasively, his anxious gaze endeavoring to pierce the darkness. “Let us go on. Take my arm, sir, and don’t be afraid of making a false step.”

“Here I am, Harry.” And they both advanced, whilst Harry looked on every side, throwing the light of his lamp into all the corners of the gallery.

“Shall we soon be there?” asked the engineer.

“In ten minutes at most.”

“Good.”

“But,” muttered Harry, “that was a most singular thing. It is the first time such an accident has happened to me.

“That stone falling just at the moment we were passing.”

“Harry, it was a mere chance.”