There was no difficulty in conversation. With the plate glass window in front of the pilot's seat and the hatch to the motor-room closed, the compartment was practically cut off, both from external and internal noises. Except for the muffled pulsations of the motors and the subdued roar from the propellers, there was little to indicate that the flying-boat was cutting through the air at eighty-five miles an hour. "It's a jolly lucky thing we didn't carry on in the motor-boat," remarked Peter. "Look down there." He pointed to the sinuous course of the river. Even at that height it was quite easy to see that the Rio del Morte above the lake was not easily navigable. There were rapids at about every half-mile, the foaming water showing up distinctly in the strong sunlight. It was doubtful whether a small boat, or any boat, could force her way against that furious torrent, rendered even more formidable by the numerous rocks that split the swiftly-running water into dangerous cascades. "Yes," agreed Uncle Brian gravely, "we did the right thing. But don't forget--more than likely the air station at San Antonio is in touch with us by means of the magnetic detectors. We've got to bear in mind the possibility of being pursued." "But they won't know what has happened," said Peter. "All they know is that the 'bus is proceeding up-country, following the course of the river. They would naturally conclude that the original crew are in pursuit of our late and unlamented 'egg-box'. Until the air station people get to hear from the fellows we left on the island--by the by, what will happen to them?" "That's not our affair now," replied Uncle Brian. "In a few days another flying-boat will be dispatched to look for them. They've plenty of water, so they won't be thirsty; and, if they're hungry--well, there's the hound. In a way, he is responsible for their present plight." "Talking of hunger," observed Peter, "isn't it about time we piped to dinner? I think I heard a suggestion about grub a couple of hours ago." His uncle agreed, and went aft to the store and provision room. A few minutes later, thanks to the stabilizing device that enabled the flying-boat to hold on her course both as regards altitude and direction, Peter and Uncle Brian were enjoying a plain but satisfying meal of the food originally intended for the ill-fated Rioguayan captain. Nor was the motor-mechanic neglected, although, when Peter opened the trap-hatch to pass the food down to him, he cowered and trembled in a state of utter funk. "Now," remarked Uncle Brian, after consulting a map, "we ought to be approaching the scene of preliminary operations. The pipe-line should be about here, running in a north-west to south-east direction. It may be overgrown with tropical growth, but I know for a fact that it was laid on the surface and not buried." "Bad system, that," observed Peter.