"I wonder if we'd better go in now, or wait until Professor Henderson is through talking to Mr. Roumann?" asked Mark.
"Yo' am to go right in," remarked Washington. "Dem's de orders I got when I went t' de statione t' meet yo'."
"All right," assented Jack. "Come on, Mark. We'll find out what's wanted of us."
The two boys entered the library, whence the voices of Professor Henderson and Mr. Roumann could still be heard in earnest discussion. Mr. Henderson looked up as his protégés advanced to the middle of the apartment.
"Jack! Mark!" he exclaimed. "I am very glad you came so promptly. I have something very important to communicate to you—something that I hope will make up for the loss you suffer in being taken away from college in the middle of the term. Or, to be more correct, Mr. Roumann will impart most of the information, for it is at his suggestion that I sent for you."
"Are these the young assistants of whom you spoke?" asked the other man, and the boys noticed that he was a big, burly German, with a bushy, gray beard, and penetrating, blue eyes.
"This is Jack Darrow," said the professor, indicating the stout youth, "and the other is Mark Sampson. They have lived with me several years now, and we have had many adventures together."
"Ha! Hum! Yes!" murmured Mr. Roumann, then he said something in German.
"I beg your pardon," he went on quickly. "I have a habit of talking to myself in my own language once in a while. What I said was that I did not know the lads were so young. I am somewhat apprehensive—"
"Do not be alarmed on the score of their youth," cried Professor Henderson. "I assure you that they have had a peculiar training, and, in some scientific attainments, they know as much as I do. You will not find them too young for our purpose, in case we decide that the thing can be done."