Toller made no comment about the exchange. He knew the two were testing him to see what style of command he was going to favour on the voyage. A strict interpretation of flight regulations would have precluded any badinage at all among his crew, let alone grossness, but he was solely concerned with their qualities of efficiency, loyalty and courage. In a couple of hours the ship would be higher than any had gone before — if one discounted the semi-mythical Usader of five centuries earlier — entering a region of strangeness, and he could foresee the little group of adventurers needing every human support available to them.

Besides, the same subject had given rise to a thousand equally coarse jokes in the officers’ quarters, ever since the utilitarian design of the skyship gondola had become common knowledge. He himself had derived a certain amusement from the frequency with which ground-based personnel had reminded him that the toilet was not to be used until the prevailing westerlies had carried the ship well clear of the base.…

The bursting of the ptertha took Toller by surprise.

He was gazing at the globe’s magnified image when it simply ceased to exist, and in the absence of a contrasting background there was not even a dissipating smudge of dust to mark its location. In spite of his confidence in their ability to deal with the threat, he nodded in satisfaction. Sleep was going to be difficult enough during the first night aloft without having to worry about capricious air currents bringing the silent enemy to within its killing radius.

“Make a note that the ptertha has just popped itself out of existence,” he said to Zavotle, and — expressing his relief — added a personal comment. “Put down that it happened about four hours into the flight… just as Flenn was using the toilet… but that there is probably no connection between the two events.” Toller awoke shortly after dawn to the sound of an animated discussion taking place at the centre of the gondola. He raised himself to a kneeling position on the sandbags and rubbed his arms, uncertain as to whether the coolness he could feel was external or an aftermath of sleep. The intermittent roar of the burner had been so intrusive that he had achieved only light dozes, and now he felt little more refreshed than if he had been on duty all night. He walked on his knees to the opening in the passenger compartment’s partition and looked out at the rest of the crew.

“You should have a look at this, captain,” Zavotle said, raising his narrow head. “The height gauge actually does work!”

Toller insinuated his legs into the cramped central floorspace and went to the pilot’s station, where Flenn and Rillomyner were standing beside Zavotle. At the station was a lightweight table, attached to which was the height gauge. The latter consisted of nothing more than a vertical scale, from the top of which a small weight was suspended by a delicate coiled spring made from a hair-like shaving of brakka. On the previous morning, at the beginning of the flight, the weight had been opposite to the lowest mark on the scale — but now it was several divisions higher.

Toller stared hard at the gauge. “Has anybody interfered with it?”

“Nobody has touched it,” Zavotle assured him. “It means that everything they told us must be true. Everything is getting lighter as we go higher! We’re getting lighter!”

“That’s to be expected,” Toller said, unwilling to admit that in his heart he had never quite accepted the notion, even when Lain had taken time to impress the theory on him in private tutorials.

“Yes, but it means that in three or four days from now we won’t weigh anything at all. We’ll be able to float around in the air like… like… ptertha! It’s all true, captain!”

“How high does it say we are?”

“About three-hundred-and-fifty miles — and that agrees well with our computations.”

“I don’t feel any different,” Rillomyner put in. “I say the spring has tightened up.”

Flenn nodded. “Me too.”

Toller wished for time in which to arrange his thoughts. He went to the side of the gondola and experienced a whirling moment of vertigo as he saw Land as he had never seen it before — an immense circular convexity, one half in near-darkness, the other a brilliant sparkling of blue ocean and subtly shaded continents and islands.

Things would be quite different if you were lifting off from the centre ofChamteth and heading out into open space, Lain’s voice echoed in his mind. But when travelling between the two worlds you will soon reach a middle zone — slightly closer to Overland than to Land, in fact — where the gravitational pull of each planet cancels out the other. In normal conditions, with the gondola being heavier than the balloon, the ship has pendulum stability — but where neither has any weight the ship will be unstable and you will have to use the lateral jets to control its attitude.

Lain had already completed the entire journey in his mind, Toller realised, and everything he had predicted would come to pass. Truly, they were entering a region of strangeness, but the intellects of Lain Maraquine and other men like him had already marked the way, and they had to be trusted.…

“Don’t get so excited that you lose the burn rhythm,” Toller said calmly, turning to Zavotle. “And don’t forget to check the height gauge readings by measuring the apparent diameter of Land four times a day.”

He directed his gaze at Rillomyner and Flenn. “And as for you two — why did the Squadron take the trouble to send you to special classes? The spring has not altered in strength. We’re getting lighter as we get higher, and I will treat any disputing of that fact as insubordination. Is that clear?”

“Yes, captain.”

Both men spoke in unison, but Toller noticed a troubled look in Rillomyner’s eyes, and he wondered if the mechanic was going to have difficulty in adjusting to his increasing weightlessness. This is what the proving flight is for, he reminded himself. We are testing ourselves as much as the ship. By nightfall the weight on the height gauge had risen to near the halfway mark on the scale, and the effects of reduced gravity were apparent, no longer a matter for argument.

When a small object was allowed to drop it fell to the floor of the gondola with evident slowness, and all members of the crew reported curious sinking sensations in their stomachs. On two occasions Rillomyner awoke from sleep with a panicky shout, explaining afterwards that he had been convinced he was falling.

Toller noticed the dreamlike ease with which he could move about, and it came to him that it would soon be advisable for the crew to remain tethered at all times. The idea of an unnecessarily vigorous movement separating a man from the ship was one he did not like to contemplate.

He also observed that, in spite of its decreased weight, the ship was tending to rise more slowly. The effect had been accurately predicted — a result of the fading weight differential between the hot gas inside the envelope and the surrounding atmosphere. To maintain speed he altered the burn rhythm to four-eighteen, and then to four-sixteen. The pikon and halvell hoppers on the burner were being replenished with increasing frequency and, although there were ample reserves, Toller began to look forward to reaching the altitude of thirteen-hundred miles. At that point the ship’s weight, decreasing by squares, would be only a fourth of normal, and it would become more economical to change over to jet power until the zone of zero gravity had been passed.

The need to interpret every action and event in the dry languages of mathematics, engineering and science conflicted with Toller’s natural response to his new environment. He found he could spend long periods leaning on the rim of the gondola, not moving a muscle, mesmerised, all physical energies annulled by pure awe. Overland was directly above him, but screened from view by the patient, untiring vastness of the balloon; and far below was the home world, gradually becoming a place of mystery as its familiar features were blurred by a thousand miles of intervening air.