So, you see, the myth story of Phaeton foreshadowed, in a way, the science story of Laplace. For, according to the Laplace theory, the world _was_ on fire; and a big rain storm, lasting for ages, with plenty of thunder and lightning, did help put it out. This theory of Laplace was long accepted as the true one. Indeed, it was only yesterday, comparatively, that other explanations were offered as to how we came to have a world to stand on. The broadest of these new theories--the one that undertakes to explain the most--is that of Professor Chamberlin, of the University of Chicago. [Illustration: THE SUN AND HIS PEBBLE WORLDS However the worlds of our solar system may have been made, when they were done there was the sun in the centre and his worlds travelling around him in their ordered orbits. Nearest the sun is Mercury. Then Venus, Earth, Mars, Jupiter, Saturn, Uranus; then, finally, Neptune nearly 3,000,000,000 miles away and with an orbit so big that Christmas comes only once in 60,000 years! ] YOU CAN SEE THESE WORLDS IN THE MAKING Owing to the more powerful telescopes of to-day, and the amount of exploring among the worlds that has been going on since the time of Laplace, several things have been discovered that have brought his theory into question. For one thing, many more nebulæ have been found in space than were known when Laplace worked out his great conception, and among them all not one has been found with a central mass surrounded by a ring. Moreover, our sharp-eyed telescopes show that Saturn's ring, which Laplace thought was a solid mass, is really made up of a great number of small satellites: baby worlds. The greater number of these nebulæ are like the ones you see in the illustration on page 5. They consist of very bright centres with spirals streaming out from opposite sides. Just take a look at the picture. Doesn't the shape of those spirals suggest that the central mass is whirling? And notice the little white lumps here and there. The thinner, veil-like portions of the mass, as well as the "lumps," are supposed to be made of particles of matter, but the lumps to be more condensed. All the particles, big and little, are known to be revolving about the central mass, much as the earth revolves about the sun. The little white lumps, or knots, in the filmy skein are supposed to be worlds in the making. Being larger than the other particles, they draw the smaller to them, according to the same law of gravitation which makes every unsupported thing on earth fall to the ground, because the earth is so much bigger than anything there is on it. Since these bright little lumps behave so much like the worlds we know as planets, and yet are relatively so small, they are called planetessimals, or "little planets." So Professor Chamberlin's idea of the origin of worlds is known as the "planetessimal theory." [Illustration: HOW YOU CAN WATCH THE WORLD TURN ROUND