The black flyer had been hit. That much was certain. It lurched and staggered in the air, losing altitude all the while. Then the pilot seemed to regain control. He swung swiftly to one side and began to rise. All the time the anti-aircraft guns were firing viciously. The tossing boat made a poor platform for the gunners, however, and their aim was inevitably poor. The guns kept up a ceaseless roaring. Puff after puff of white smoke showed where their shells burst near Varrhus. He began to swerve, to zigzag, using tactics strangely like those of a dragon fly. Suddenly he darted to a point exactly above the small boat, and a smoky cloud began to dart down from below his machine. Varrhus passed on, but the cloud fell swiftly, precisely like the cloud of liquified gas he had poured down on Teddy and Davis above New York harbor. "Flares!" cried Davis in an agony of apprehension, though his voice was only audible to Teddy by means of the telephone connection between the two helmets. As he spoke the men on the boat shot up the little fire balls that had protected the aëroplane in its former fight. A dozen balls of light sped up to meet the menacing cloud of liquified gas. They reached it, sped into it, glowing feebly! The white cloud did not ignite, but fell on toward the boat. It reached and enveloped the little vessel, and suddenly the guns were still. "Damn him!" said Teddy in a voice that shook with rage. "He's not using hydrogen. We can't close in on him now. Our flares are no good." Davis tilted the nose of his machine upward, and Teddy stared down his sights. He pulled the trigger. The gun kicked backward, but the recoil cylinders did their work. The tracer shell left a little line of smoke behind it. It passed below the black body. "Too low," said Teddy grimly, and fired again. Varrhus began to climb. Straight up his machine went, but with the picric acid giving added impetus to the explosions in the cylinders the two-seater climbed as rapidly. Varrhus' ascent swerved. He was directly over the aëroplane. A whitish cloud appeared below his machine and blotted it out for an instant. "We zoom," said Davis almost gayly, and the fighting plane seemed to be dancing on its tail for an instant. The cloud of gas unfolded itself down to the surface of the water, barely twenty yards before the space in which Davis had checked his course. Around and around a huge circle. The biplane had caught up with the black flyer, and Davis turned toward it for an instant to give Teddy an opportunity to fire. There was a flash at the stern of the slender black body, and the symmetry of the glistening form was marred by a ragged edge where the tip of the tail had been blown off. "Almost," said Teddy grimly. "He'll dive now."