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 partial explosions," 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, ten years older, often saw the last
'monk' working in the mine. He was called so because he wore a long robe
like a monk. His proper name was the 'fireman.' At that time there was
no other means of destroying the bad gas but by dispersing it in little
explosions, before its buoyancy had collected it in too great quantities
in the heights of the galleries. The monk, as we called him, with his
face masked, his head muffled up, all his body tightly wrapped in a
thick felt cloak, crawled along the ground. He could breathe down there,
when the air was pure; and with his right hand he waved above his head
a blazing torch. When the firedamp had accumulated in the air, so as to
form a detonating mixture, the explosion occurred without being fatal,
and, by often renewing this operation, catastrophes were prevented.
Sometimes the 'monk' was injured or killed in his work, then another
took his place. This was done in all mines until the Davy lamp was
universally adopted. But I knew the plan, and by its means I discovered
the presence of firedamp and consequently that of a new seam of coal in
the Dochart pit."

All that the old overman had related of the so-called "monk" or
"fireman" was perfectly true. The air in the galleries of mines was
formerly always purified in the way described.

Fire-damp, marsh-gas, or carburetted hydrogen, is colorless, almost
scentless; it burns with a blue flame, and makes respiration im