. "I not only think, but I feel
convinced, that the mischief has begun. Moreover, I am determined that
it shall end before it goes any further. I am most anxious to discover
who is at the bottom of it, and in this I want you to help me."

"Want _me_ to help!" exclaimed Derrick, in astonishment.

"Yes, you," answered Mr. Jones, smiling. "Your very youth and
inexperience will render you less likely to be suspected than an older
person. I am certain that I can count upon the son of my old friend
Gilbert Sterling to perform truly and faithfully any duty which his
employers may see fit to intrust him with. Is it not so, Derrick?"

"Yes, sir, it is," cried the boy. "Just tell me what you want me to do,
and if I don't succeed it won't be because I haven't tried my best."

"That is just what I expected you to say," remarked the mine boss,
quietly. "Now we will lay our first plans. I suppose you have had enough
of the breaker, haven't you?"

"Indeed I have, sir."

"Very well. For a change I am going to offer you a job in the mine where
I will give you a bumping-mule to drive. Your wages will be five dollars
a week."

"A bumping-mule?" queried Derrick, in a tone of perplexity not unmixed
with disappointment. From the preceding conversation he had expected to
be intrusted with something very different from mule-driving; nor had he
any idea what sort of an animal the one in question might be.

This time Mr. Jones not only smiled but laughed outright; for, from the
boy's face and tone, he easily understood what was passing in his mind.

"A bumping-mule," he explained, "is the animal that draws the loaded
coal-cars from the chambers, or breasts, to where they are made up into
trains. These trains are then hauled by a team of mules to the foot of
the slope. Then, when the empty cars are brought back, the bumping-mule
distributes them to the several places where they are required. I
suppose his title comes from his causing the cars to bump together as he
makes them up into trains. In attending to your duties as driver of this
most important mule, I can assure you that your time will be fully
occupied from the minute you go into the mine until you leave it.

"I suppose," he added, with a humorous twinkle in his eyes, "that our
conversation led you to think you were to be appointed 'air boss' of the
mine, or placed in charge of a gang at the very least?"

"No, sir," answered Derrick, a little hesitatingly; "I ain't quite such