The bird is safe from the tempest for a brief moment, but immediately passes from winter to winter again. So man’s life appears for a little while, but of what is to follow, or of what went before, we know nothing. If, therefore, a new doctrine tells us something certain, it seems to deserve to be followed. These words, originally spoken in advocacy of the Christian religion, describe what is perhaps the main interest of astronomy to-day. Man only knowing Life’s little lantern between dark and dark wishes to probe further into the past and future than his brief span of life permits. He wishes to see the universe as it existed before man was, as it will be after the last man has passed again into the darkness from which he came. The wish does not originate solely in mere intellectual curiosity, in the desire to see over the next range of mountains, the desire to attain a summit commanding a wide view, even if it be only of a promised land which he may never hope himself to enter; it has deeper roots and a more personal interest. Before he can understand himself, man must first understand the universe from which all his sense perceptions are drawn. He wishes to explore the universe, both in space and time, because he himself forms part of it, and it forms part of him. We may well admit that science cannot at present hope to say anything final on the questions of human existence and human destiny, but this is no justification for not becoming acquainted with the best that it has to offer. It is rare indeed for science to give a final “Yes” or “No” answer to any question propounded to her. When we are able to put a question in such a definite form that either of these answers could be given in reply, we are generally already in a position to supply the answer ourselves. Science advances rather by providing a succession of approximations to the truth, each more accurate than the last, but each capable of endless degrees of higher accuracy. To the question, “where does man stand in the universe?” the first attempt at an answer, at any rate in recent times, was provided by the astronomy of Ptolemy: “at the centre.” Galileo’s telescope provided the next, and incomparably better, approximation: “man’s home in space is only one of a number of small bodies revolving round a huge central sun.” Nineteenth-century astronomy swung the pendulum still further in the same direction, saying: “there are millions of stars in the sky, each similar to our sun, each doubtless surrounded, like our sun, by a family of planets on which life may be kept in being by the light and heat received from its sun.” Twentieth-century astronomy suggests, as we shall see, that the nineteenth century had swung the pendulum too far; life now seems to be more of a rarity than our fathers thought, or would have thought if they had given free play to their intellects.