"Well, here's where I look for diamonds," called Jack, as he stepped boldly out, followed by Mark. "Let's see who'll find the first sparkler." "All right," agreed his chum, and they strolled away together, slightly in advance of the two professors and Andy, who remained together, the scientist discussing the phenomena on every side and the hunter looking in vain for something to shoot. But he had come to a dead world. Almost before they knew it Jack and Mark had gone on quite some distance. Though they were not aware of it at that moment, it was much easier to walk on the moon than it was on the earth, for they weighed only one sixth as much, and the attraction of gravitation was so much less. But suddenly Jack remembered that curious fact, and, stooping, he picked up a stone. He cast it from him, at the same time uttering a yell. "What's the matter?" called Mark. "Look how far I fired that rock!" shouted Jack. "Talk about it being easy! why, I believe I could throw a mile if I tried hard!" "It goes six times as far as it would on the earth," spoke his chum, "and we can also jump six times as far." "Then let's try that!" proposed Jack. "There's a nice level place over there. Come on, I'll wager that I can beat you." "Done!" agreed Mark, and they hurried to the spot, their very walking being much faster than usual. "I'll go first," proposed Jack, "and you see if you can come up to me." He poised himself on a little hummock of rock, balanced himself for a moment, and then hurled himself through space. Prepared as he was, in a measure, for something strange, he never bargained for what happened. It was as if he had been fired from some catapult of the ancient Romans. Through the air he hurtled, like some great flying animal, covering fifty feet from a standing jump. "Say, that's great!" yelled Mark. "Here I come, and I'll beat----" He did not finish, for a cry of horror came from Jack. "I'm going to fall into a crater--a bottomless pit! I'm on the edge of it!" yelled the lad who had jumped. And, with horror-stricken eyes, Mark saw his chum disappear from sight beyond a pile of rugged rocks, toward which he had leaped. The last glimpse Mark had was of the life-torch, which Jack held up in the air, close to his head. "Jack--in a crater!" gasped Mark, as he ran forward, holding his own life-torch close to his mouth and nose. CHAPTER XXI WASHINGTON SEES A GHOST Advancing by leaps and bounds, and getting over the ground in a manner most surprising, Mark soon found himself on the edge of the great, yawning crater, into which his chum Jack had started to slide. I say started, for, fortunately, the lad had been saved from death but by a narrow margin.