Frigate checked the altimeter and then rotated a metal drum set in the overhead. This was attached by a rope to a wooden valve in the neck of the bag. It opened, releasing some gas. The balloon sank. It would shortly begin rising again, though, which meant more gas would have to be valved off. This called for operation of the torch at intervals, and also for shutting off the torch and feeding hydrogen into the balloon.
It required cool and accurate judgment to know just how much gas to valve and how much to replace. Too much valved off meant a too fast fall. Too much new gas meant that the craft could ascend beyond the pressure height. A safety valve on top of the bag would automatically release gas to prevent bursting of the bag-if the valve hadn’t frozen-but the balloon would then become, possibly, too heavy.
In addition, the pilot had to watch out for unexpectedly warm layers of air. These could lift the Jules Verne too swiftly and carry it above the pressure height. A sudden cooling off could precipitate the craft downward.
The pilot could in the latter situation order ballast thrown out, but this might result in a yoyo morion. And if he lost all his ballast, he was in trouble. The only way to lose altitude quickly was to release more gas. Which meant that the burner might not be able to expand the hydrogen quickly enough.
Nobody Knows the Troubles I’ve Seen would be his swansong. However, the day passed without any nerve-wracking emergencies. The sun sank, and the Jules Verne, its hydrogen cooling, did likewise. The pilot had to run the burner just enough to raise it now and then and keep the vessel above the tropopause. Those off-duty snuggled under heavy cloths and slept according to their natures. Being the only one awake at night was eerie. The illumination was feeble. The starlight poured into the ports, but this, with some small lights above the gauges and dials, was not enough for comfort. The alloy hull amplified every noise: the impact of a hand on the deck as somebody turned over and flung out an arm; Pogaas muttering Swazi; Frisco grinding his teeth; Rider softly whinnying horselike; the fan whirring.
When Frigate ignited the torch, the sudden explosion and succeeding roar startled everybody from sleep. Then it was his turn to burrow under the cloths, to sleep, to be roused momentarily by the torch or a nightmare of falling.
Dawn came. The crewmen got up at different times, used the chemical toilet, drank hot instant coffee or tea, and ate food saved from the grails, supplemented by acorn bread and dried fish. The wastes from the toilet were not jettisoned. Opening a hatch at this altitude meant a possibly fatal drop in air pressure, and any weight loss increased the lift.
The Frisco Kid, whose eye was best at estimating ground speed, though they were clipping along at 50 knots.
Before noon, the vessel was gripped by a wind that took them backward for several hours before it curved the craft around northeast again. After three hours they were going southward again.
“If this keeps up we’ll whirl around here forever,” Frigate said gloomily. “I don’t understand this.”
Late that afternoon they were back on the proper course. Frigate said that they should descend to the surface winds and try their luck there. They were far enough north to be where the winds generally flowed toward the northeast.
By letting the burner stay off, the gas slowly cooled. The Jules Verne sank at a minuscule rate at first, then began dropping swiftly. Nur turned the burner on for a few minutes to check its descent. At 13 kilometers altitude, the wind lessened. It picked up again and in an opposite direction, the wrong one for them. It also gave the craft a counterspin. Nur allowed it to sink until it was about 2000 meters above the mountaintops. Now they moved at an angle across the valleys, which were running straight north and south in this area.
“We’re going northeast again!” Frigate said happily.
At high noon of the third day they were sailing along at an estimated 25 kmph or more than 15 mph. Only the Jules Verne could have gotten this far. Any other type of balloon would not have been able to ascend to the stratosphere or descend to the surface winds without losing too much gas to go on.