The grave profile of the astronomer showed through the dim light from the shrouded electric lamp like the head of an ancient statue of some Greek philosopher. Before him lay a litter of white papers covered with figures and an open book of logarithms. Immured in the interior of the great dome, with its monumental walls like those of an ancient Egyptian pyramid, they could hear no sound save the slow tick of the sidereal clock and the faint whir of the complicated machinery that drove the telescope in its infallible following of the movements of the solar system. For upward of two minutes, Thornton remained unconscious of Hooker's presence. Then, with a sigh, he laid down his pencil and, looking up, observed his friend for the first time. "Hello, Bennie," he exclaimed, with a suggestion of excitement in his ordinarily calm voice; "pull your chair up here! We've got something big--the biggest thing, in fact, that has ever happened in astronomy! We got the elements of Battelli's comet yesterday. Unless I've made some mistake in my figures, there's going to be a smash-up in the universe!" From Thornton, the conservative, such a declaration had immeasurable significance. "You mean it's going to hit the earth?" asked Hooker, with interest. "No," answered Thornton; "but it looks as if it would strike one of the smaller asteroids in a head-on collision--and if it does--" "Something will drop," finished Hooker. "Which asteroid?" "Medusa--one I've been following in its orbit for more than two years--a small planet, largely composed of pitchblende." Hooker pursed his lips into a whistle. "What do you really suppose will happen?" he inquired. "No one can tell," replied, the astronomer. "The collision might check Medusa in its orbit and cause it to fall into the sun. In falling, it might cross the earth's path and strike us--it might mean the end of the world!" "Gee whiz!" ejaculated Professor Hooker. "When is this interesting event going to take place?" "I calculate that the comet and the asteroid will come into collision at three o'clock on the morning of the eighteenth of next month. You can come over and see it if you like." "I'll be here," Bennie assured him, jotting down the date. "And now," he added, pulling his note-book from his pocket, "be a good fellow and solve this equation for me, will you?" "Good Lord!" protested Thornton. "Really, don't you think it's almost bedtime? I'm no good outside my own line, anyway." "This _is_ your line," retorted Bennie. "Look here, Thornton; don't go back on me. All this fooling-around of mine with radium and that sort of stuff has weakened my mathematics. I've simply got to solve this equation. I almost solved it this morning," he added, with a shamefaced recollection of the girl in the tan suit. "There's no use your calling on me," answered Thornton definitely. "It would take a week for me to catch up with you, anyhow." Hooker's face clearly showed his disappointment.