down into the mine
again to-morrow."

"Indeed I think I must, sir," said Derrick, earnestly. "I don't believe
any one else can get along with Harry Mule as well as I can."

"Let me see. How many years have you been driving him?" asked Mr. Jones,
gravely.

"Only one day, sir," replied Derrick laughing, "but I think he's very
fond of me, and I know I am of him."

"All right; if you insist upon it, you shall go down again to-morrow to
your bumping-mule. Now I want to talk to you seriously."

The conversation that followed was long and earnest, and it was ended by
Mr. Jones saying, just before he left, "I must manage somehow or other
to be there on the 27th, and I want you to go with me, for I don't know
anybody else whom I dare trust. It only remains for us to discover a
way."

CHAPTER VIII

DERRICK STERLING'S SPLENDID REVENGE

The new breaker, in which Paul Evert now worked as a slate-picker, was
in general appearance very much like the old one, but its interior
arrangement was different, and of such a nature as to make life much
easier for those who worked in it. The greatest improvement was the
introduction of a set of machines called "jigs." The coal from the mine,
after being drawn to the very top of the breaker, first passed between
great spiked rollers, or "crushers;" then through a series of "screens,"
provided with holes of different sizes, that separated it into several
grades of egg, stove, nut, pea, buckwheat, etc. From the screens it was
led into the jigs. These are perforated iron cylinders set in tubs of
water, and fitted with movable iron bottoms placed at a slight angle. A
small steam-engine attached to each machine raises and lowers or "jigs"
this iron bottom a few inches each way very rapidly. The contents of the
cylinders are thus constantly shaken in water, and as the slate is
heavier than the coal, most of it settles to the bottom, and is carried
off through a waste chute. The wet coal runs out through other chutes
placed a little higher than that for slate, and extending down through
the length of the breaker to the storage bins at its bottom. Along these
chutes in the new breaker, as in the old one, sat rows of boys picking
out the bits of slate that had escaped the jigs, and among them was Paul
Evert.

When Derrick Sterling entered the new breaker on the afternoon of the
day following that which had brought such memorable adventures, he was
surprised at the comparative absence o