“And do you think,” asked Thorwald, “that the myriads of stars were also made simply to delight the eye of man?” “How do I know that they were not?” the doctor asked in reply. “Because of the absolute unreasonableness of the thought, if for no other reason,” answered Thorwald. “But now let me recall to your mind more of the knowledge possessed by the inhabitants of the earth. I think I know about what that knowledge is, from my acquaintance with the present state of your development. Astronomy has been our master science, and I can remember fairly well the extent of our knowledge when we had reached your stage. If I should fall into the error of attributing to you more than you have already discovered you can easily correct me. “If, now, you leave the little group of dark bodies which are so like the earth, and go out still further into space, what do you find? At distances so great that only the speed of light can be used as a measuring line, you discover vast numbers of self-luminous bodies, which you call stars. Your natural eye can tell but a small fraction of their number. For example, look at the constellation you have named the Pleiades and you see six or seven stars. View it through a three-inch telescope and you can count perhaps three hundred. Now attach a photographic plate to the telescope, and with an exposure of four hours the light coming from that small patch of sky falls upon the sensitive film with a cumulative effect until you have a picture of more than two thousand three hundred stars.” “Yes,” broke in the doctor, “you are gauging correctly the state of our knowledge. Our largest telescopes reveal in the entire sky, it is said, one hundred million stars.” “Then,” answered Thorwald, “if the glories of the heavens were made merely to delight the eye of man, why was not the eye created of sufficient power to behold them? As it is, only a small proportion of the stars can be seen without the aid of instruments too costly and too delicate for general use. “But have you the means of establishing any likeness between the earth and those distant bodies? You have discovered that the law of gravitation is universal and that the motions of the stars resemble those of the solar system. Have you made any discoveries tending to prove the existence of other systems like our own?”