“Now what you must understand is that light can be reflected, refracted, polarized, but never destroyed.” He pointed to his instruments on one of the tables. “_I_ can do all those things to it—and a thousand more—but I cannot destroy it.” “Right,” said Tubby. “But if you put it out you can’t never get it back, can you now?” The professor beamed on him genially. “Your brain works too keenly,” he said. “You anticipate me. No, _I_ cannot get it back. But it comes back. That’s just the point—it comes back. That’s what nobody in the world knows except me—me and you. “The sun,” he went on, “gives us most of our light—it gets here to the earth from the sun in a few minutes. The moon gives us reflected sunlight. It is the same light, only it comes to us from the sun by way of the moon. It takes a little longer that way.” “How much?” Tubby asked. “Not much—just a few seconds—the moon is not far away. Now all this light that strikes the earth is reflected back into space. In a hundred years—less or more according to the distance—it strikes the different stars. There it mingles with other light. And then, mark me well, and then”—the professor paused impressively—“then in another hundred years it comes back to us again—the same light—mixed with other light of course—but some of the same light we had two hundred years before. Do you understand?” “No—yes,” said Tubby. “That,” said the professor, “is the _Oats Theory of the Rationality of Light_. I call it that because it _is_ rational—it is in accordance with all known physical laws. “Some others I could name”—the professor’s voice shook with suppressed passion; his eyes gleamed again wickedly—“some others are not so scrupulous. _Their_ theories do _not_ coincide with recognized physical laws—they transgress them all. Mere astronomical outcasts—mathematical lepers—scientific pariahs—” “Oh—you mean that other guy?” said Tubby. The professor calmed himself with an effort. He pulled a huge black silk handkerchief from his pocket and mopped his dripping forehead. “We won’t talk of him,” he said after a moment. “No, we better leave him out of it,” Tubby agreed. “Ain’t I right?” The professor nodded. “Now we come to _my_ great discovery. I’ll tell you about that now. “When this sunlight is reflected from the moon to us, it brings with it an image of the moon, which was not in the light when it left the sun. Do you understand?” “No—yes,” said Tubby. “That’s why we can see the moon—the light brings us the image. All light carries an image of something—that’s why we can see things. “Now when light leaves the earth and goes out into space it takes with it an image of the earth and everything that is happening on the earth.” “Right,” said Tubby. “Go on.”