Gradually, the luminous discharge from Medusa increased in brilliancy until the planet became a ball of fire. Giant sheets of yellow light, like aurora streamers, drove off from its surface as the deadly ray bored against it until the asteroid resembled a vast volcanic eruption. Under the fierce blast from the Ring, its surface was melting away, and driving out into space a glowing mass of incandescent gas. Burning thus, out in the blackness of space, it resembled a conflagration--the burning-up of a powder factory--seen at a safe distance through the night. A safe distance? Unexpectedly, out of the darkness, a shower of moving points of light appeared in the ether, around the asteroid, darting hither and yon, growing larger momentarily as, shining in the light of the sun, they traced luminous lines across the sky. Medusa was returning the attack! The explosions upon the planet's surface were hurling great fragments of rock and stone in every direction, filling space with flaming missiles, contact with the smallest of which meant death to the daring voyagers in the Ring. Several of these molten fragments hurtled by the windows, blazing fiercely but making no sound, while some, encountering others in their flight, exploded silently, like distant rockets breaking in the zenith. Everywhere the heavens were a mass of shooting-stars of every conceivable color--green, purple, blue, orange, yellow, red, and lilac--a kaleidoscopic display of surpassing beauty, of fearful wonderment. It was as if some demigod had emptied a furnace into the heavens, scattering its glowing contents throughout the sky, or as if a million bombs at pointblank range were bursting on every side and discharging showers of fireworks about the Ring. But already Medusa had commenced her retreat, already her disk appeared smaller, and to prolong the bombardment meant only unnecessary danger to the occupants of the car. "I guess we've given her 'what for,'" commented Burke. "She's running away from us. Shall we let up?" Bennie signaled to Atterbury to throw off the current, and the conflagration on the asteroid ceased as suddenly as it had started. The volcanic bombs continued to fly by them at occasional intervals, but presently the last one passed, and they breathed freely again. They had escaped. Their work was done. The earth was saved. They could return. II "They could return." How easy to say the words--as easy as it had been to fly off by means of their radioactive power from the surface of the earth! But, now that the necessity of returning whence they had come presented itself, they suddenly realized difficulties which had hitherto not suggested themselves. While they had paralleled the course of Medusa, they had been headed straight for the earth, which hung in the sky above them, a gigantic crescent of a dazzling bluish white, its oceans and continents barely discernible through the haze of its atmosphere.