They had not lost their love for making queer voyages, and one of their greatest desires was to help the professor turn out a craft even more wonderful than the Electric Monarch, the Porpoise or the Flying Mermaid. It was in this connection that Jack was experimenting on the new gas, when the slight accident happened. "Are you going to try that again?" asked Mark, as he and his chum walked along to their geometry class. "Sure," replied Jack. "I want that to succeed. I know I am on the right track." "You came near getting blown off the track," remarked his companion, which was as near to a joke as he ever would come, for, though Jack was jolly and full of fun, Mark was more serious, inclined to take a sterner view of life. "Oh, I'll succeed yet!" exclaimed Jack. "And when I do--you'll see something--that's all." "And feel it, too," added Mark, putting his hand on his head, the book having raised quite a lump. It was several days after this before the boys had the chance to work alone in the laboratory again, and Jack had to promise not to try his experiment with the new gas before this privilege was granted him. "Want any help?" asked Dick Jenfer, another student, as he saw Jack and Mark enter the laboratory. "Yes, if you want to hold a test tube for me," answered Jack. "I'm going to try a new way of making oxygen." "No, thanks! Not for mine!" exclaimed Dick as he turned away. "I don't want to be around when you try your new experiments. The old way of making oxygen is good enough for me." "Well, I have a new scheme," went on Jack. Soon he and Mark, whom he had again induced to help him, were busy with test tubes, rubber hose, Bunsen flames, jars of water, and all that is required to make oxygen. Somewhat to his own surprise, the experiment Jack tried was a success. He collected a jarful of oxygen, generated in a way he had thought out for himself. It was much simpler than the usual method. Just as he concluded the test, some one opened the laboratory door. It was Professor Lenton. "I have a telegram for you," he said. "A telegram?" "Yes. It just arrived." Jack tore open the yellow envelope. "It's from Professor Henderson," he said. "Is anything the matter?" asked Mark. "I don't know," answered Jack. "It says: 'Come home at once.' I wonder what's wrong?" "I hope nothing serious," said Professor Lenton. "You may both prepare to leave this afternoon. I am sorry. Let me hear from you when you reach Professor Henderson. I trust nothing has happened to him. He is too great a scientist for us to lose." CHAPTER III WASHINGTON MEETS THE BOYS All thoughts of experiments were driven from the minds of Jack and Mark by the telegram. They imagined that something had happened to their old friend, and it worried them. If he was dangerously hurt, as might be, for he was constantly experimenting in a small way, it would mean that a great change must take place in their lives.