The Properties of Matter as Illustrated by the Stars

When Professor Aitken and Dr. Evermann did me the honor to ask me to speak before you today, I chose a large subject. I hope that you will not conclude that my motive was that of the inexperienced preacher who always took a whole chapter for his text, so that he was persecuted in one city, he might flee to another/' But let me proceed to my topic, saying only that most of what I will say deals with other men's work, and but little with my own. Among the many properties of matter which are illustrated by the stars, I shall confine myself to those which are primarily properties of atoms, for there has been an amazing development in the last decade or two, both in our knowledge of the stars and in that of atoms, and the two are becoming more and more intimately associated, as I hope to show you this afternoon. Let us begin with a bit of history. Rather more than fifty years ago, we first found ourselves in possession of a means of investigating the properties of matter in distant regions of the universe, by means of the spectroscope. We all know how the absorption in the atmosphere of the stars of the light which comes from deeper down, produces the dark in the spectra, and that each individual constituent of the atmosphere, whether element or compound, absorbs its own distinctive the same which it would emit if its vapor were raised to a high enough temperature. The pioneer work of the sixties showed at once that many of the familiar terrestrial elements hydrogen, iron, sodium, calcium, and so on were present in the atmospheres of the Sun and the stars. Later investigations have revealed the presence of about fifty of the terrestrial elements in the Sun, and of many in the stars, and practically all the in these spectra (except the faintest, which have not yet been fully studied) are now identified with known lines which can be produced in the laboratory.