Robin put the end of the air tube in his mouth. Peter pushed the homemade helmet down over his head, secured it tightly, almost painfully, until no space was left for air to escape. Then Peter reached behind Robin to the small tank strapped there and turned a petcock. Instantly Robin started to choke as he felt something being rammed down his lungs. He caught himself, recognizing that his lungs were being forcibly inflated. He struggled to get control of his diaphragm to expel the excess air pressure. He managed finally to do so, feeling a whiff of air rush through his nostrils. He fought a bit more with the unpleasant current, felt himself getting a grip on it. Through the plate of his helmet he saw Peter watching him anxiously. Then Peter rapidly tied the nylon cord around his own waist, let it out a few feet, and tied the other end around Robin's. Peter snapped shut the visor of his own helmet, touched the air controls of his own suit, and nodding to Robin, stepped out into the tunnel. Robin followed closely, conscious of the tight, restricting bands, still fighting the unpleasant pressure of the air tube blowing down his lungs. Peter walked a few steps, pointed a gloved hand across the passage, shone his light. There was a narrow black gap across there. Through it Robin caught a glimpse of bright white specks--the stars! Then Peter made a dash, seemed to be picked up by a giant hand and whirled wildly across the passage. The cord tightened and Robin jumped into the space to avoid being pulled off his feet. He was struck at once by a terrific onrush. A hot, violent blast slammed into him. He lost his footing, felt himself being hurled headlong into a furious tornado. The cord leaped out, and Peter pulled on it hard. Robin swung about, fetched up against the other side of the wall of the cave with a bang, was pulled to his feet before he had even started to fall, and was propelled right through the gap in the wall. Suddenly all was still. The whistling of the wind, the roar of the current as it struck him, had vanished. Only the sucking and rushing of the oxygen in his own helmet could be heard. He was outside, on the surface of the Moon at last! The gap opened from the wall of a cliff. Above him, the cliff soared to become a mountainous edge of a deep, wide crater. He turned his head, but Peter was impatient. He felt the pull of the cord, turned and followed Peter, who was moving away from the crater wall in long, low strides, strides that ate up distance like an Earthly giant in seven-league boots. Robin adjusted his pace, followed closely. For a while he forgot his personal danger and simply gazed around at the fabulous moonscape. The crater's other wall was maybe a dozen miles away, but the thin air--the almost indetectably tenuous air that clustered at the bottom of this crater made the distance seem nothing. He could even make out details of the far edge.