"Wow! Then maybe we'd better not go," said Jack, with a shiver. "What will we do, if we get thirsty?" "Oh, I guess we can manage, with all the apparatus we have, to distill enough water," said Professor Henderson, with a smile. "Then, too, we will take plenty with us, and, of course, tanks of oxygen to breathe. But it will be interesting to see if there are people on the moon." "If there are any, they must have a queer time," went on Mark. "Why?" asked Jack, who wasn't very fond of study. "Why? Because the moon is only about one forty-ninth the size of the earth. Its diameter is 2,163 miles--only a quarter of the earth's--and, comparing the force of gravity, ours is much greater. A body that weighs six pounds on the earth, would weigh only one pound on the moon, and a man on the moon could jump six times as high as he can on this earth, and throw a stone six times as far." "What's dat?" inquired Washington White quickly, nearly dropping some packages he was carrying into the projectile. "What was yo' pleased t' saggasiate, in remarkin' concernin' de untranquility ob the densityness ob stones jumpin' ober a man what is six times high?" he asked. "Do you mean what did I say?" asked Mark solemnly. "Dat's what I done asked yo'," spoke the colored man gravely. "Well, you didn't, but perhaps you meant to," went on the youth, and he repeated his remarks. "'Scuse me, I guess I'd better not go on dish yeah trip after all," came from Washington. "Why not?" demanded Professor Henderson. "'Cause I ain't goin' t' no place whar ef yo' wants t' take a little jump yo' has t' go six times as far as yo' does when yo' is on dis yeah earth. An' s'posin' some ob dem moon men takes a notion t' throw a stone at me? Whar'll I be, when a stone goes six times as far as it does on heah? No, sah, I ain't goin'!" "But perhaps there are no men on the moon," said Mark quickly. "It is only a theory of astronomers that I'm talking about." "Oh, only a theory; eh?" asked Washington quickly. "That's all." "Oh, if it's only a theory, den I reckons it's all right," came from the colored man. "I didn't know it were a theory. Dat makes it all right. It's jest in theory, am it, Massa Mark, dat a stone goes six times as far?" "That's all." "Oh, well, den, why didn't yo' say so fust, dat it was only a theory? I don't mind theories. I--I used t' eat 'em boiled an' roasted befo' de wah." And, with a contented smile on his face, Washington went into the projectile, to finish stowing things away in his kitchen lockers. The big projectile was housed in the shed where it had been constructed, and the professor and the boys were working over it there, carefully guarded from curious eyes, for the German inventor did not want the secret of his Cardite motor to become known. The work went on from day to day, good progress being made. The boys were of great assistance, for they were practical mechanics, and had had considerable experience.