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.
Even as they watched it, they could observe its rotation as one can detect the movement of the minute-hand of a clock. The moon had presented no such problem. It was dead, almost without axial motion. But the earth was very much alive, whirling on its axis with a speed at the equator of a thousand miles an hour—nearly that of a shell from a rifled cannon. How could they land upon it? Theirs seemed to be the superhuman task of the clown who tries to climb upon the revolving table at the circus—an impossibility. When they had left the earth, they had assimilated this axial motion, and, in steering their course through the ether, they had allowed for it, as the navigator allows for the tide or the set of the current. But now, on their arrival at the globe's surrounding atmosphere, they would be attempting to land upon a ball revolving with a velocity of ten or fifteen times that of the fastest express-train.
"We could land at either of the poles," suggested the research professor. "Of course there wouldn't be any motion there!"
"Yes; we might do that," agreed Bennie; "or"—and he scratched his head—"we can navigate the Ring toward the earth in a spiral orbit. Anyhow, the Ring has got to follow the earth in her orbit around the sun."