The black speck ahead of them was drawing no nearer, it is true, but it was not dwindling. The silvery wings of the biplane cut through the air with fierce impatience. It flew in the straightest of straight lines after the other craft. Dark-brownish smoke blew backward from the bellowing exhausts, tinged almost to saffron by the presence of the explosive acid. The sunlight kissed the upper surfaces of the wings of the pursuing plane. Below them the ocean rolled and tossed. Whistling wind and roaring engines. Speed, speed, speed! The biplane rushed with incredible swiftness through the air. The black flyer skimmed lightly on, barely in advance of its white-winged enemy. Twice Teddy essayed a shot, but the biplane trembled so that accuracy was impossible, and he could see by the smoke of his tracer shell that he had gone far wide of the black machine. The space between the black speck and the waves below it seemed to increase. "Rising," said Davis. "Now we'll get him." Teddy kept his eyes fixed on Varrhus' slender, needlelike craft. He was barely conscious of the upward tilt of the machine in which he was riding, but he saw that they were keeping pace with Varrhus as he rose in the air. "Four thousand feet," said Davis crisply. "And two hundred and twenty-nine miles an hour. There's land ahead." Teddy saw a mountainous coast line becoming visible far away. The black flyer continued to rise. "Six thousand feet," said Davis again, "and two hundred and thirty-two miles----" The pilot of the other machine saw that they were gaining. He dropped abruptly. "Now!" exclaimed Davis fiercely. He dived downward. The descent, coupled with the immense power of the engines--now delivering vastly more than the eight hundred horse power for which they were designed--made them shoot toward the black flyer with increasing speed. The other machine was barely more than half a mile away and every detail of its construction was visible. Teddy noticed for the first time a slender tube rising between the two center sustaining propellers. He instantly leaped to the conclusion that it was the means by which the jets of liquified gas had been shot out. He fired. "A hit!" cried Davis. There had been a flash from the top of the cabin. A jagged rent appeared in the polished roofing, and the slender tube vanished. The black flyer seemed to abandon all hopes of escape. It sped madly for a gap between two of the tall mountains that rose along the coast line. At the unprecedented speed with which both machines had been traveling the coast seemed fairly to rush at them. No villages were visible, but it seemed to be a habitable, if not an inhabited, land. The black flyer swept on across country, Varrhus evidently making every effort to gain even a few yards on his adversaries, and Davis just as fiercely determined that he should not. Once, twice, three times Teddy fired.