They were gone all that day, returning very much discouraged at dusk, saying that they could get no trace of him. "I don't see where he can be!" exclaimed Jack desperately, for, though the two lads were not related, they had been friends so long, and had shared so many pleasures and dangers together, that they were like brothers. "You won't start for the moon until you find him, will you, Professor?" asked Jack. "No, indeed; though we could start to-morrow if he was here," replied the aged scientist. "The special tools came to-day, and the motor has been repaired. We have tested it, and the Cardite power works even better than did the Etherium apparatus." "Then we can start as soon as Mark is found?" asked Andy Sudds. "Yes, for everything has been put inside the projectile, and all that remains is to haul it out of the shed, point it at the moon, and start the motor." "Then I guess I'll give my gun a final cleaning, and get ready. There may be good hunting on the moon," said the old hunter. Jack was tired from his long tramp that day, searching for his missing chum, but before he went to bed he wanted to go out and take a look at the big projectile, which was now ready to start for the moon. As he turned around the corner of the immense shed to enter the door, he was startled by seeing a figure coming toward him. Jack started, rubbed his eyes, and peered again. "Is it possible? Can I be mistaken?" he whispered. The figure came nearer. Jack, who had come to a halt, broke into a run. "Mark! Mark!" he cried joyously. "Oh, you've come back! Where have you been?" Jack was about to clasp his chum in his arms when he saw that Mark's arm was in a sling, and that his face was all bandaged up, so that scarcely any of his features showed. Had it not been for the clothes, and a certain stoutness of which Mark never could seem to get rid, Jack would scarcely have known his friend. "Why, Mark, what happened?" cried Jack. "Have you met with an accident? Where have you been? In a hospital? What became of you? Why didn't you wait for me?" "I can't answer all those questions at once," was the reply, and Jack thought Mark's voice was curiously muffled and hoarse, entirely unlike his usual tones. But he ascribed that to the bandages around the mouth. "Well, answer one at a time then," said Jack, and there was an undefinable, strange air about his chum which cooled Jack's first impulse of gladness. "Whatever happened to you, Mark? Are you hurt?" "I was--yes," came the reply, in short, jerky tones. "I had an accident, and I've been in a hospital. That's why I couldn't send you word. But I'm all right now. When does the projectile start?" "To-morrow, now that you're here. But tell me more about it. Where were you hurt?" "On my head and arm." "No; I mean where did the accident occur?" "Oh, in the old house where I went to--to look for that man." "Did you find him?" asked Jack eagerly. "No. He's not there now."