what remains of the
Aberfoyle mines? But for what reason? I will find that out, if it should
cost me my life!"

A fortnight before the day on which Harry Ford guided the engineer
through the labyrinth of the Dochart pit, he had been on the point of
attaining the object of his search. 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. And when they
talked over these phenomena, evidently due to a physical cause, "My
lad," the old man would say, "we must wait. It will all be explained
some day."

However, it must be observed that, hitherto, neither Harry nor his
father had ever been exposed to any act of violence. If the stone which
had fallen at the feet of James Starr had been thrown by the hand
of some ill-disposed person, it was the first criminal act of that
description.

James Starr was of opinion that the stone had become detached from
the roof of the gallery; but Harry would not admit of such a simple
explanation. According to him, the stone had not fallen, it had been
thrown; for otherwise, without rebounding, it could never have described
a trajectory as it did.

Harry saw in it a direct attempt against himself and his father, or even
against the engineer.

CHAPTER VI. SIMON FORD'S EXPERIMENT

THE old clock in the cottage struck one as James Starr and his two
companions went out. A dim light penetrated through the ventilating
shaft into the glade. Harry's lamp was not necessary here, but it
would very soon be of use, for the old overman was about to conduct the
engineer to the very end of the Dochart pit.

After following the principal gallery for a distance of two miles,
the three explorers--for, as will be seen, this was a regular
exploration--arrived at the entrance of a narrow