The air grew stifling, for the expended energy of the enemies' rays must needs be absorbed. It could not disintegrate them nor decompose their bodies, but the contacts were many and the liberation of heat enormous. They were suffocating! But Karl would not desist. They drove on, now beneath, now above an enemy ship. He lost count. One of his own vessels was in trouble. The report came to him from the little speaker at his ear. He looked around in alarm. A glowing object reeled uncertainly over there between two of the aeros of the Zar. The concentration of beams of vibrations was too much for the sturdy craft. It was red hot and its occupants burned alive where they sat. Suddenly it slipped into a spin and went slithering down into the city, leaving a gaping opening where it fell. This sobered him somewhat, but he went into the battle with renewed fury. * * * * * How many had they brought down? Fifteen? Sixteen? He tore his purple jacket from his body. The perspiration rolled from his pores. His own ship would be next. But what did it matter? Kill! Kill! He shouted once more into the microphone, then dived into battle. Another and another! In Heaven's name, how many were there? It was maddening. If only he could breathe. His lungs were seared; his eyes smarting from the heat. And then it was over. Three of the Zar's aeros remained, and these turned tail to run for it. No! They were falling, nose down, under full power; diving into the city from which they had come. Suicide? Yes. They couldn't face the recriminations that must come to them. And anything was better than facing that burning death from the strange little fighters which had come from out the skies. Dorn was a mass of wreckage. Karl tore at the fastenings of the ports, searing his fingers on the heated metal. His pilot had collapsed, the little aero heading madly skyward with no guiding hand. Air! They must have air! He loosened the pilot's jacket; slapped frantically at his wrists in the effort to bring him to consciousness. Then he was at the controls of the vessel, tugging on first one, then the other. The aero circled and spun, executing the most dangerous of sideslips and dives. A little voice was speaking to him--the voice of the radio--instructing him. In a daze he followed instructions as best he could. The whirlings of the earth stabilized after a time and he found he was flying the vessel; climbing rapidly. * * * * * A sense of power came to him as the little voice of the radio continued to instruct. Here were the controls of the electronic motor; there the gravity-energy. He was proceeding in the wrong direction. But what did it matter? He learned the meaning of the tiny figures of the altimeter; the difference between the points of the compass. Still he drove on.