“We seem to have lost a good bit of speed during the night, captain,” Zavotle reported from the pilot’s station. “The rip line is getting quite taut — though, of course, you can’t rely on it much any more.”

“It’s time for the jet, anyway,” Toller said. “From now on, until turn-over, we’ll use the burner only enough to keep the balloon inflated. Where’s Rillomyner?”

“Here, captain.” The mechanic emerged from the other passenger compartment. His pudgy figure was partially doubled over, he was clutching the partitions and his gaze was fixed on the floor.

“What’s the matter with you, Rillomyner? Are you sick?”

“I’m not sick, captain. I… I just don’t want to look outside.”

“Why not?”

“I can’t do it, captain. I can feel myself being drawn over the side. I think I’m going to float away.”

“You know that’s nonsense, don’t you?” Toller thought of his own moment of unmanning fear and was inclined towards sympathy. “Is this going to affect your work?”

“No, captain. The work would help.”

“Good! Carry out a full inspection of the main jet and the laterals, and make very sure we have a smooth injection of crystals — we can’t afford to have any surges at this stage.”

Rillomyner directed a salute towards the floor and slouched away to fetch his tools. There followed an hour of respite from the full burn rhythm while Rillomyner checked the controls, some of which were common to the downward-facing jet. Flenn prepared and served a breakfast of gruel studded with small cubes of salt pork, all the while complaining about the cold and the difficulty he was having in keeping the galley fire going. His spirits improved a little when he learned that Rillomyner was not going to eat, and as a change from lavatorial humour he subjected the mechanic to a barrage of jokes about the dangers of wasting away to a shadow.

True to his earlier boast, Flenn seemed quite unaffected by the soul-withering void which glimmered through chinks in the decking. At the end of the meal he actually chose to sit on the gondola wall, with one arm casually thrown around an acceleration strut, as he goaded the unhappy Rillomyner. Even though Flenn had tethered himself, the sight of him perched on the sky-backed rim produced such icy turmoil in Toller’s gut that he bore the arrangement for only a few minutes before ordering the rigger to descend.

When Rillomyner had finished his work and retired to lie down on the sandbags, Toller took up his position at the pilot’s station. He entered the new mode of propulsion by firing the jet in two-second bursts at wide intervals and studying the effects on the balloon. Each thrust brought creaks from the struts and rigging, but the envelope was affected much less than in experimental firings at low altitudes. Encouraged, Toller varied the timings and eventually settled on a two-four rhythm which acted in much the same manner as continuous impulsion without building up excessive speed. A short blast from the burner every second or third minute kept the balloon inflated and the crown from sagging too much as it nosed through the air.

“She handles well,” he said to Zavotle, who was industriously writing in the log. “It looks as though you and I are going to have an easy run for the next day or two — until the instability sets in.”

Zavotle tilted his narrow head. “It’s easier on the ears, too.”

Toller nodded his agreement. Although the jet was firing for a greater proportion of every minute than the burner had been doing, its exhaust was not being directed into the great echo chamber of the balloon. The sound of it was flatter and less obtrusive, quickly absorbed by the surrounding oceans of stillness.

With the ship behaving so docilely and according to plan Toller began to feel that his forebodings of the night had been nothing more than a symptom of his growing tiredness. He was able to dwell on the incredible idea that in a mere seven or eight days, all being well, he was due to have a close look at another planet. The ship could not actually touch down on Overland, because doing so would involve pulling out the rip panel, and with no inflation facilities it would be unable to depart again. But it was to go within a few yards of the surface, dispelling the last traces of mystery about conditions on the sister planet.

The thousands of miles of air separating the two worlds had always made it difficult for astronomers to say much more than that there was an equatorial continent spanning the visible hemisphere. It had always been assumed, partly on religious grounds, that Overland closely resembled Land, but there remained the possibility that it was inhospitable, perhaps because of surface features beyond the resolving power of telescopes. And there was the further possibility — an article of faith for the Church, a moot case for philosophers — that Overland was already inhabited.

What would the Overlanders look like? Would they be builders of cities? And how would they react on seeing a fleet of strange ships float down from the sky?

Toller’s musing was interrupted by the realisation that the coldness in the gondola had intensified in a matter of minutes. Simultaneously, he was approached by Flenn, who had the pet carble clutched to his chest and was visibly shivering. The little man’s face was tinged with blue.

“This is killing me, captain,” he said, trying to force his customary grin. “The cold has got worse all of a sudden.”

“You’re right.” Toller felt a stirring of alarm at the idea of having crossed an invisible danger line in the atmosphere, then inspiration came to him. “It’s since we eased off on the burner. The blow-back of miglign was helping to keep us warm.”

“There was something else,” Zavotle added. “The air streaming down over the hot envelope would have helped as well.”

“Damn!” Toller frowned up into the geometric traceries of the balloon. “This means we’ll have to put more heat in there. We have plenty of green and purple — so that’s all right — but there’s going to be a problem later on.”

Zavotle nodded, looking gloomy. “The descent.”

Toller gnawed his lip as, yet again, difficulties unforeseen by the earthbound S.E.S. scientists confronted him. The only way for the hot-air craft to lose altitude was through shedding heat — suddenly a vital commodity as far as the crew were concerned — and to make matters worse the direction of the air flow would be reversed during the descent, carrying the reduced amount of warmth upwards and away from the gondola. The prospect was that they would have to endure days in conditions very much worse than those of the present — and there was a genuine possibility that death would intervene.

A dilemma had to be resolved.

Was the fact that so much depended on the outcome of the proving flight an argument for going on and on, even at the risk of passing an imperceptible point of no return? Or was there a higher obligation to be prudent and turn back with their hard-won store of knowledge?

“This is your lucky day,” Toller said to Rillomyner, who was watching him from his usual recumbent position in a passenger compartment. “You wanted work to occupy your mind, and now you’ve got it. Find a way of diverting some heat from the burner exhaust back down into the gondola.”

The mechanic sat up with a startled expression. “How could we do it, captain?”

“I don’t know. It’s your job to work out things like that. Rig up a scoop or something, and start right now — I’m tired of seeing you lie around like a pregnant gilt.”

Flenn’s eyes gleamed. “Is that any way to talk to our passenger, captain?”

“You’ve spent too much time on your backside, as well,” Toller told him. “Have you needles and thread in your kit?”

“Yes, captain. Big needles, little needles, enough threads and twines to rig a sailing ship.”

“Then start emptying sandbags and making over-suits out of the sacking. We’ll also need gloves.”