"I'll take her down to eight thousand feet," continued Peter briskly. "Then I'll get you to stand by, Uncle. There's nothing to be done except to watch the altimeter and the compass. There's no need to bust along now. We've ten hours of darkness in front of us and we don't want to find ourselves miles out over the Atlantic when day breaks. I'll cut out the after motors." In spite of the fact that the interior of the fuselage was heated by pipes connected with the exhausts, the air within the cabins was bitterly cold, and the temperature fell yet lower after the rear pair of motors was shut down. Peter was now feeling very sleepy. Lack of proper rest, the excitement of the last two days, and the effect of the rarefied atmosphere all combined to reduce him to a state of resistless drowsiness. "You turn in," said his uncle peremptorily. "I'm good for another ten hours, if needs must. If there's anything requiring your attention, I'll wake you." The elder man "took on". Since the flying-boat was built largely after his designs, he was well acquainted with the technical part of the mechanism and construction, but he was quite a novice in the art of actual flight. As long as things went right, there was little for him to do. Peter, wrapped in half a dozen blankets in addition to a leather flying-coat, was soon sound asleep in spite of the low temperature. He had not slept for more than ten minutes when his uncle roused him. "She's faltering--both engines," announced Uncle Brian laconically. Peter rose stiffly to his feet. He had not the trained ear for mechanism that his uncle possessed, and as far as he could hear, the motors were still keeping up their rhythmic purr. "Look at the gauge of the main fuel tank," suggested Uncle Brian. His nephew picked up an electric torch and made his way to the 'midship compartment. He went sceptically enough, but on consulting the indicator, the state of the gauge fairly startled him. It stood at zero. That meant that only one of the auxiliary tanks contained any kerosene, and owing to its position was useless unless the flying-boat was diving steeply or in an inverted position while "looping". The tanks were three-quarters full when the flying-boat had passed out of Rioguayan control; and since only a few hours had elapsed, it was a matter of impossibility for the four motors even running all out to "mop up" anything like the quantity that had gone somewhere. A hasty examination revealed the cause of the leakage. A drain-cock was half open, allowing a steady stream of kerosene to flow into space. At first thoughts, Peter attributed the leakage to the Rioguayan mechanic, until he remembered that the fellow had been locked up when left alone on board. But there was little time for speculation.