As they drifted along the now familiar corridor of the Alpha Airlock complex, Norton wondered if they had let impatience overcome caution. They had waited aboard Endeavour for forty-eight hours—two precious days—ready for instant departure if events should justify it. But nothing had happened; the instruments left in Rama had detected no unusual activity. Frustratingly, the television camera on the Hub had been blinded by a fog which had reduced visibility to a few metres and had only now started to retreat.

When they operated the final airlock door, and floated out into the cat’s-cradle of guide-ropes around the Hub, Norton was struck first by the change in the light. It was no longer harshly blue, but was much more mellow and gentle, reminding him of a bright, hazy day on Earth.

He looked outwards along the axis of the world—and could see nothing except a glowing, featureless tunnel of white, reaching all the way to those strange mountains at the South Pole. The interior of Rama was completely blanketed with clouds, and nowhere was a break visible in the overcast. The top of the layer was quite sharply defined; it formed a smaller cylinder inside the larger one of this spinning world, leaving a central core, five or six kilometres wide, quite clear except for a few stray wisps of cirrus.

The immense tube of cloud was bit from underneath by the six artificial suns of Rama. The locations of the three on this Northern continent were clearly defined by diffuse strips of light, but those on the far side of the Cylindrical Sea merged together into a continuous, glowing band.

What is happening down beneath those clouds? Norton asked himself. But at least the storm, which had centrifuged them into such perfect symmetry about the axis of Rama, had now died away. Unless there were some other surprises, it would be safe to descend.

It seemed appropriate, on this return visit, to use the team that had made the first deep penetration into Rama. Sergeant Myron—like every other member of Endeavour’s crew—now fully met Surgeon-Commander Ernst’s physical requirements; he even maintained, with convincing sincerity, that he was never going to wear his old uniforms again.

As Norton watched Mercer, Calvert and Myron “swimming” quickly and confidently down the ladder, he reminded himself how much had changed. That first time they had descended in cold and darkness; now they were going towards light and warmth. And on all earlier visits, they had been confident that Rama was dead. That might yet be true, in a biological sense. But something was stirring; and Boris Rodrigo’s phrase would do as well as any other. The spirit of Rama was awake. When they had reached the platform at the foot of the ladder and were preparing to start down the stairway, Mercer carried out his usual routine test of the atmosphere. There were some things that he never took for granted; even when the people around him were breathing perfectly comfortably, without aids, he had been known to stop for an air check before opening his helmet. When asked to justify such excessive caution, he had answered: “Because human senses aren’t good enough, that’s why. You may think you’re fine, but you could fall flat on your face with the next deep breath.”

He looked at his meter, and said “Damn!”

“What’s the trouble?” asked Calvert.

“It’s broken—reading too high. Odd; I’ve never known that to happen before. I’ll check it on my breathing circuit.”

He plugged the compact little analyser into the test point of his oxygen supply, then stood in thoughtful silence for a while. His companions looked at him with anxious concern; anything that upset Karl was to be taken very seriously indeed.

He unplugged the meter, used it to sample the Rama atmosphere again, then called Hub Control.

“Skipper! Will you take an O2 reading?”

There was a much longer pause than the request justified. Then Norton radioed back: “I think there’s something wrong with my meter.”

A slow smile spread across Mercer’s face.

“It’s up fifty per cent, isn’t it?”

“Yes, what does that mean?”

“It means that we can all take off our masks. Isn’t that convenient?”

“I’m not sure,” replied Norton, echoing the sarcasm in Mercer’s voice. “It seems too good to be true.” There was no need to say any more. Like all spacemen, Commander Norton had a profound suspicion of things that were too good to be true.

Mercer cracked his mask open a trifle, and took a cautious sniff. For the first time at this altitude, the air was perfectly breathable. The musty, dead smell had gone; so had the excessive dryness, which in the past had caused several respiratory complaints. Humidity was now an astonishing eighty per cent; doubtless the thawing of the Sea was responsible for this. There was a muggy feeling in the air, though not an unpleasant one. It was like a summer evening, Mercer told himself, on some tropical coast. The climate inside Rama had improved dramatically during the last few days…

And why? The increased humidity was no problem; the startling rise in oxygen was much more difficult to explain.

As he recommenced the descent, Mercer began a whole series of mental calculations. He had not arrived at any satisfactory result by the time they entered the cloud layer.

It was a dramatic experience, for the transition was very abrupt. At one moment they were sliding downwards in clear air, gripping the smooth metal of the handrail so that they would not gain speed too swiftly in this quarter-of-a-gravity region. Then, suddenly, they shot into a blinding white fog, and visibility dropped to a few metres. Mercer put on the brakes so quickly that Calvert almost bumped into him—and Myron did bump into Calvert, nearly knocking him off the rail.

“Take it easy,” said Mercer. “Spread out so we can just see each other. And don’t let yourself build up speed, in case I have to stop suddenly.”

In eerie silence, they continued to glide, downwards through the fog. Calvert could just see Mercer as a vague shadow ten metres ahead, and when he looked back, Myron was at the same distance behind him. In some ways, this was even spookier than descending in the complete darkness of the Raman night; then, at least, the searchlight beams had shown them what lay ahead. But this was like diving in poor visibility in the open sea.

It was impossible to tell how far they had travelled, and Calvert guessed they had almost reached the fourth level when Mercer suddenly braked again. When they had bunched together, he whispered: “Listen! Don’t you hear something?”

“Yes,” said Myron, after a minute. “It sounds like the wind.”

Calvert was not so sure. He turned his head back and forth, trying to locate the direction of the very faint murmur that had come to them through the fog, then abandoned the attempt as hopeless.

They continued the slide, reached the fourth level, and started on towards the fifth. All the while the sound grew louder—and more hauntingly familiar. They were halfway down the fourth stairway before Myron called out: “Now do you recognize it?”

They would have identified it long ago, but it was not a sound they would ever have associated with any world except Earth. Coming out of the fog, from a source whose distance could not be guessed, was the steady thunder of falling water.

A few minutes later, the cloud ceiling ended as abruptly as it had begun. They shot out into the blinding glare of the Raman day, made more brilliant by the light reflected from the low-hanging clouds. There was the familiar curving plain—now made more acceptable to mind and senses, because its full circle could no longer be seen. It was not too difficult to pretend that they were looking along a broad valley, and that the upward sweep of the Sea was really an outward one.