"Several years ago Professor Milton was in need of some dye for some obscure purpose. One of his assistants made a wisecrack to the effect that if Professor Milton was so smart, why couldn't he filter the dye out of ink and use that. Milton devised a filter capable of separating the dye from ink, and used it. So far the filter is useless for anything else but it will certainly remove the color from a bottle of ink, leaving the stuff in two useless quantities." "Interesting, but--" "Astronomically, the idea of separating the world into two hemispheres is disastrous." * * * * * "Why?" asked Ingalls. "I know little of astrology." Edwards glared at him. "Not astrology; astronomy. Astrophysics or celestial mechanics. Your half-apple of a world is unstable astronomically. Gravity would set in unfavorably upon the instant of division and separation and the half-apple would collapse into two smaller spheres, gradually assuming true spherical shapes in thousands of years as the rocks cold-flowed. But for the moment, the shock and the immediate crack-up would leave no city standing; huge crevices would be formed, and no living thing to remain. Understand, I'm a doctor of medicine and not an astrophysicist. My description may err but I can guarantee that the results would be disastrous. I suggest that if you don't believe me, call one of the big brains at Mount Palomar; they'll tell you the details." [Illustration: The shock of splitting the earth would leave no city standing; huge crevices would be formed, and no living thing would remain.] "It sounds impossible. But if the man is a maniac--" "Not a maniac," objected Doctor Harris. "Just completely single-track, literal-minded. Genius without judgement. Cares nothing for any problem that has not caught his fancy but will pursue anything he likes to the bitter end. Trying to keep up with what he fancies is like predicting which way a bar of bath soap will squirt when you step on it inadvertently. He's--" "Enough! Convinced or not, I'll aid you to re-collect the Professor. How shall we go about it?" "You're the man-hunter," said Edwards with a smile. "How do you go about it?" "Just what kind of thing will this mad genius use to divide the earth?" asked Ingalls. "Lord knows," grunted Harris. "Why?" "I was suggesting that we keep watch over the sale of certain materials." "Make it a watch over _all_ materials," snorted Edwards. "Field theory is an abstract subject and he'll try to reduce it to practise, I'd guess. Mechanical division is impossible, I'd state flatly. Gravity holds the earth together; slicing it would do no good for it would cold-pressure weld together once the knife passed. But with some sort of field to divide and direct the forces of gravity--Well, your guess is as good as mine."