Thus fed, he sat down and began to map out his course. I must do things systematically, he told himself. I must keep track of time, set up a regular pattern of living, find a permanent base of operations. I shall have to explore this cavern and those beyond it, find all possible enemies and invent ways and means of defending myself. I shall have to breed my rabbits in quantity, find a way of using their pelts and fur. I shall have to determine a use for everything left from the rocket's material--metals and the like. For, he continued telling himself, my one aim shall be to stay alive long enough to be found some day by exploring rockets from Earth. I am a Robinson Crusoe of a new world. Crusoe waited twenty-eight years for rescue, I must be as courageous. In his case, he had no evidence that any ship would ever bother to call on him. In my case I know that rockets are being made that will eventually lead to further Moon trips. I know that men are planning to come here. I must wait it out, even for twenty-eight years. But it was not that simple and he knew it. But first things first, and the first task was to survive. With the monkey scampering on ahead, he set out to walk to the cavern wall. He found it to be dark and glistening, a lavalike sheet resembling the bubble it was. Leaning against it and looking upward, he saw that it curved gradually up, and that indeed he was in a flaw within a very porous world. Like the inside of a Clark candy bar, he thought, with a wry smile. Astronomers on Earth had always been puzzled by the lightness of the Moon. They had speculated on it as being mainly pumice. Lately there had been much speculation and opinion holding forth the theory that the Moon was porous, had these bubbles and air pockets all through it, that the Moon's water and atmosphere had all gone underground to be sealed off in these hollow spaces. He now knew they were right. Most of these Moon bubbles, large enough to hold cities, must be entirely sealed off. But others were linked, sometimes broken into by quakes or the volcanic action which was still going on in the depths of what had once been considered a dead world. This particular cavern was such a bubble. Robin walked along the outer wall and saw a dark black spot in it, and then others. He came to them, found they were breaks in the surface, pocks caused by smaller bubbles. He looked into one that opened at the base. Using his flashlight, he could see that it was a small, almost entirely spherical cave. He found others pocking the walls of the cavern bubble. This then was the ideal spot for a permanent home. Not that he needed shielding from the elements, for obviously there were no elements here--no rain, snow, clouds, or weather oddities. Neither was there night or day.