Sure enough, there was a dark underground channel through whose center rushed the eternal current of hot volcanic air. This channel probably had its source somewhere in the still-mysterious depths of the Moon's core. It wound and forced its way upward doubtless to dissipate somewhere, as the cold of the surface bore away its warmth, probably to wind up downward again as a mass of cold gas. There was barely enough room at the side of the tunnel for a man to stand flat against the wall, without touching the blast. Robin, who had gone through to examine it, came back out into the light of Korree's cave. "Well," he asked Peter, "what do we do now?" His brother nodded. "I think we can get to the surface all right. Just get in the blast and let ourselves be blown along upward. When we find that break, we'll get out of the current and we'll be able to reach our rocket." "Uh huh," said Robin, "and then how do we get back down here again?" Peter shrugged. "I don't know. There must be a way." The two returned to their own place and talked it over. But the opportunity was too good to pass up. "Sooner or later," said Robin, "we're going to do it. So we may as well face that. As for getting back, perhaps we could simply walk all the way down the channel, keeping carefully to the side of dead air just beyond the blast." Peter frowned. "I don't think you'll find much of that. There can't be many places where such a dead air channel exists. On the other hand, if we attack the problem of returning by the old route, we may be able to find a way through it from that end--or make a new one. Back at the rocket there are explosives, better tools than those we have. I think we should risk it." "Yes," Robin added, "I think so too. Besides, we ought to fire off some more flares. Our signals may never have been seen." That being settled, the two Earthlings again donned their space suits, equipped themselves, tied themselves together with a length of cord. They returned to Korree's cave, explained their project and gravely shook hands with their Glassie friend. Then Robin carefully eased himself through the break into the dark channel. Peter squeezed through after him, as Robin flattened himself along the wall and moved aside. Their helmets sealed, Robin counted to three, and then both leaped forward. Instantly the racing wind current caught them up, snatched them off their feet. They found themselves being blown madly along the darkness like leaves before a gale. The air was hot and Robin felt himself almost scorched as he was hurled along, his elbows and legs occasionally scraping the wall, once feeling himself somersaulting upward, twisting and turning in the horrible blast.