So they changed places, and the mule was so greatly pleased at having got his own way that he began to plunge down the stairs with great rapidity. Derrick felt almost as though he were being rushed through space on the tail of a comet, and shuddered to think of the broken limbs and general destruction that must inevitably follow such reckless travelling. The mule, however, seemed to know what he was about as well as the man who led him, and took such good care of himself that Derrick soon plucked up courage, and even began to enjoy the situation. As he was thinking that they must be somewhere near the centre of the earth, the mule gave an unusually violent plunge forward, and then stopped so suddenly that poor Derrick found himself sprawling on the animal's back, with both arms clasped tightly about his neck. With this the mule began to caper and shake himself so violently that the boy was forced to loose his hold and fall to the ground, amid roars of laughter from a score of miners who witnessed the scene. Greatly confused, Derrick scrambled to his feet, gave a reproachful glance at the mule, which was calmly gazing at him with a wondering look in his wide-open eyes, and turned to see in what sort of a place he had been so unceremoniously landed. At the same moment Mr. Jones, dressed in miner's costume, and looking as grimy as any of the others, stepped from the laughing group and said, "My boy, I congratulate you on being the first person who ever rode into this mine on mule-back, I am glad you found the travelling-road so good. Came on your own mule too. How did you know this was the bumping-mule you were to drive?" "I didn't know what sort of a mule he was until just as we got here and he bumped me off his back," replied Derrick; "and I begin to think that he knows more about driving than I do." "Well, you have made a notable beginning," said the mine boss, "and I am sure you two will get along capitally together. Harry Mule, this is Derrick Sterling, who is to be your new driver, and I want you to behave yourself with him." Then to Derrick he said, "Harry has the reputation of being the most knowing, and at the same time the most perverse, mule in the mine. I believe though he only shows bad temper to those who abuse him, and I have selected you to be his driver because I know you will treat him kindly, and give him a chance to recover his lost reputation. If he does not behave himself with you, I shall put him in the tread-mill. Now stand there out of the way for a few minutes, and then I will show you where you are to work."