Twice in one month, Harry, whilst visiting the west end of the pit,
distinctly heard distant reports, as if some miner had exploded

a charge of dynamite. The second time, after many careful researches,
he found that a pillar had just been blown up.

By the light of his lamp, Harry carefully examined
the place attacked by the explosion. It had not been made

in a simple embankment of stones, but in a mass of schist,
which had penetrated to this depth in the coal stratum.

Had the object of the explosion been to discover a new vein?
Or had someone wished simply to destroy this portion of the mine?

Thus he questioned, and when he made known this occurrence
to his father, neither could the old overman nor he himself

answer the question in a satisfactory way.
"It is very queer," Harry often repeated. "The presence of an

unknown being in the mine seems impossible, and yet there can
be no doubt about it. Does someone besides ourselves wish to find

out if a seam yet exists? Or, rather, has he attempted to destroy
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 physicaloccurrence, 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 phenomenon的复数">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 principalgallery 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 tunnel. It was like a nave,

the roof of which rested on woodwork, covered with white moss.
It followed very nearly the line traced by the course of the river Forth,

fifteen hundred feet above.
"So we are going to the end of the last vein?" said James Starr.

"Ay! You know the mine well still."
"Well, Simon," returned the engineer, "it will be difficult to go

further than that, if I don't mistake."
"Yes, indeed, Mr. Starr. That was where our picks tore out the last

bit of coal in the seam. I remember it as if it were yesterday.
I myself gave that last blow, and it re-echoed in my heart more

dismally than on the rock. Only sandstone and schist were round
us after that, and when the truck rolled towards the shaft,

I followed, with my heart as full as though it were a funeral.
It seemed to me that the soul of the mine was going with it."

The gravity with which the old man uttered these words impressed
the engineer, who was not far from sharing his sentiments.

They were those of the sailor who leaves his disabled vessel--
of the proprietor who sees the house of his ancestors pulled down.

He pressed Ford's hand; but now the latter seized that of
the engineer, and, wringing it:

"That day we were all of us mistaken," he exclaimed. "No! The old
mine was not dead. It was not a corpse that the miners abandoned;

and I dare to assert, Mr. Starr, that its heart beats still."
"Speak, Ford! Have you discovered a new vein?" cried the engineer,

unable to contain himself. "I know you have! Your letter could
mean nothing else."

"Mr. Starr," said Simon Ford, "I did not wish to tell any
man but yourself."

"And you did quite right, Ford. But tell me how, by what signs,
are you sure?"

"Listen, sir!" resumed Simon. "It is not a seam that I have found."
"What is it, then?"

"Only positive proof that such a seam exists."
"And the proof?"

"Could fire-damp issue from the bowels of the earth if coal
was not there to produce it?"

"No, certainly not!" replied the engineer. "No coal, no fire-damp.
No effects without a cause."

"Just as no smoke without fire."
"And have you recognized the presence of light carburetted hydrogen?"

"An old miner could not be deceived," answered Ford. "I have met
with our old enemy, the fire-damp!"

"But suppose it was another gas," said Starr. "Firedamp is almost
without smell, and colorless. It only really betrays its presence

by an explosion."
"Mr. Starr," said Simon Ford, "will you let me tell you

what I have done? Harry had once or twice observed something
remarkable in his excursions to the west end of the mine.

Fire, which suddenly went out, sometimes appeared along the face
of the rock or on the embankment of the further galleries.

How those flames were lighted, I could not and cannot say.
But they were evidently owing to the presence of fire-damp,

and to me fire-damp means a vein of coal."
"Did not these fires cause any explosion?" asked the engineer quickly.

"Yes, little partialexplosions," replied Ford, "such as I
used to cause myself when I wished to ascertain the presence

of fire-damp. Do you remember how formerly it was the custom
to try to prevent explosions before our good genius, Humphry Davy,

invented his safety-lamp?"
"Yes," replied James Starr. "You mean what the 'monk,' as the men

called him, used to do. But I have never seen him in the exercise
of his duty."

"Indeed, Mr. Starr, you are too young, in spite of
your five-and-fifty years, to have seen that. But I,