“Yes,” replied the doctor, “our recent investigations of the periods of some of the variable stars show irregularities in brightness, period, and proper motion. A close study of these irregularities has convinced some of our astronomers that there are invisible bodies near them, evidently planets circling around a central sun. The theory is that the dark bodies cause slight perturbations in the star, which account for the irregularities in period, motion, etc. So Neptune was discovered by the effect it had upon the observed movements of Uranus. This is the first evidence we have had tending to prove that there are other groups of worlds like ours, and it is considered quite significant.” “I can readily believe it,” said Thorwald, “and I know how helpful every bit of evidence is, in your search for knowledge. But if I mistake not you have the aid of another instrument, which is destined to play an important part in your future studies. You get much nearer those distant orbs when a spectroscope is placed at the end of the telescope, and the ray of light coming from sun and star is widened out into a band of color, which tells a marvelous story. That light, that has been for years, and perhaps for centuries, on its way to you, now discloses the very nature of the substances which compose those fiery globes. And what are those substances? It must have been a startling truth to the man who first read from the spectrum of the star he was studying, that it contained matter with which he was familiar, materials of which the earth itself is made. By this science you have learned beyond doubt that many of the commonest elements of the earth’s crust exist also in other worlds, and, what is of great significance, that the materials most closely connected with living organisms on the earth, such as hydrogen, sodium, magnesium, and iron, are the very ones which are found most widely diffused among the stars. I think I am not wrong in assuming that you are somewhat acquainted with the spectroscope and have made these discoveries.” “You are quite right,” said the doctor. “This branch of scientific investigation has already been carried so far with us, and the results of the experiments are so constant and uniform, that when it is asserted, for example, that such and such a metal is present in a state of vapor in the sun’s atmosphere, it is estimated that the chances in favor of the correctness of the assertion are as 300,000,000 to 1.”