"Are you in earnest in proposing this trip?" asked Professor Henderson of Jack. The lad, with flushed face and bright eyes, stood in the centre of the apartment, holding the paper which the aged scientist had returned to him. "I certainly am," was the reply. "It ought not to be a difficult undertaking, after our trip to the North Pole through the air, the one to the South Pole under water, our journey to the centre of the earth, and our flight to Mars. Why, a trip to the moon ought to be a little pleasure jaunt, like an automobile tour. Can't we go, Professor?" "From the standpoint of possibility, I presume we could make a trip to the moon," the scientist admitted. "It would not take so long, nor would it be as dangerous, as was our trip to Mars. And yet, I don't know that I care to go. I am getting along in years, and I have money enough to live on. Even a field of diamonds hardly sounds attractive to me." Jack's face showed the disappointment he felt. "And yet," went on the aged scientist with a smile, "there are certain attractions about another trip through space. I had hoped to settle down in life now, and devote my time to scientific study and the writing of books. But this is something new. We never have been to the moon, and----" "There are lots of problems about it that are still unsolved!" cried Jack eagerly. "You will be able to discover if the moon has an atmosphere and moisture; and also what the other side--the one that is always turned away from us--looks like." "It does sound tempting," went on the aged scientist slowly. "And we could do it in our projectile, the _Annihilator_. It is in good working order; isn't it, Professor Roumann?" "Couldn't be better. If you ask me, I, for one, would like to make a trip to the moon. It would give me a better chance to test the powers of Cardite, that wonderful red substance we brought from Mars. I can use that in the Etherium motor. If you left it to me, I'd say, 'go to the moon.'" "Well, perhaps we will," spoke Mr. Henderson thoughtfully. "You'll go, too, won't you, Mark?" asked Jack. "Oh, I'm not going to be left behind. I'll go if the rest do, but I don't believe you'll find any diamonds on the moon. If there ever were any, the Martians took them." For Mark had been partly convinced after the confirmation by the two professors of Jack's translation. "I'll take a chance on the sparklers," said his chum. "But now, let's go into details, and figure out when we can start. It ought not to take very long to get ready." As has been explained in detail in the other books of this series, Professor Amos Henderson and the two lads, Mark Sampson and Jack Darrow, had undertaken many strange voyages together. Sometimes they were accompanied by friends and assistants, while Washington White, a sort of servant, helper, and man-of-all-work, and Andy Sudds, an old hunter, always went with them.