He was going over the southwest end of the mine, with a large lantern in his hand.

All at once, it seemed to him that a light was suddenly extinguished, some hundred feet before him, at the end of a narrow passage cut obliquely through the rock.

He darted forward.
His search was in vain.

As Harry would not admit a supernatural explanation for a physical occurrence, he concluded that certainly some strange being prowled about in the pit.

But whatever he could do, searching with the greatest care, scrutinizing every crevice in the gallery, he found nothing for his trouble.
If Jack Ryan and the other superstitious fellows in the mine had seen these lights, they would, without fail, have called them supernatural, but Harry did not dream of doing so, nor did his father.