Page:Popular Science Monthly Volume 31.djvu/141

Rh trust "The Open Court" will become a potent influence favoring the reduction to a scientific platform of the principles and precepts of these great departments of human interest.

We do not understand that the presentation of the "Monistic philosophy" is intended to make the successor of "The Index" an organ of any theory of knowledge or being; for, while philosophy is not to be disparaged, it is far better to stand firmly upon science, and thence reach outward and onward to philosophy with much caution. If the prime object of the journal is the scientific study of morals and religion, it is not likely to become conspicuously a vehicle for the expression of speculation, but will, as "The Index" used to do, make the practical work of improving men's lives and promoting the organic growth of society its chief end, quite irrespective of philosophical or metaphysical doctrine.

general problem of the chemical constitution of the sun's atmosphere, to which the author has given a large share of his attention for many years, is among the newest and freshest, as well as one of the grandest and most fascinating, questions which science has yet attempted to answer. Although astonishing progress has already been made in this field, considering the difficulties encountered, yet the work is so vast that the time of many observers must be devoted to it before it can be said to be more than begun. The first step in the direction of spectrum analysis was taken by Kepler, who, one hundred and fifty years before Newton, observed the decomposition of white light by the prism. Nothing further was done till Newton took up the subject, and by reasoning and experiment greatly enlarged our knowledge of it. Another period of a century and a half elapsed, and then Wollaston discovered that the spectrum of sunlight is divided into several portions by dark lines. In 1814 and the following years the first great advances in spectrum examination were made. Fraunhofer constructed a map of the solar spectrum, on which he marked no less than five hundred and seventy-six dark lines, and these have ever since been known as Fraunhofer lines. His attempts to account for the lines satisfied him that they were not due to any terrestrial cause, but that "they have their origin in the nature of the light of the sun." He introduced the use of the telescope for observing the beam of light after its passage through the prism. He also introduced the method of observing stellar spectra which is still employed, and he investigated the spectra of artificial light-sources. Sir David Brewster discovered that dark lines were produced in the spectrum when nitrous-acid gas was interposed between the prism and the source of light. Many of these lines seemed to him to be identical in position with some of the Fraunhofer lines in the solar spectrum, and he accordingly felt himself justified in announcing the discovery of nitrous-acid gas in the atmosphere of the sun. This was the first chemical touch in solar inquiry. He also stated his belief that all the Fraunhofer lines were due to some absorption at the sun. Foucault then discovered that the bright lines from a colored light had the same places as the dark absorption bands from the same source. In 1852 Professor Stokes first proposed an explanation of this phenomenon, and the same idea was published by Ångström in the following year. The famous discoveries of Kirchhoff and Bunsen began to appear in 1859. Among the earliest of these was that the absorber must be cooler than the radiator. Stokes had suggested that the presence of many terrestrial elements might be detected in the sun's atmosphere by a comparison of the spectra of these elements with the Fraunhofer lines, in the way that sodium had already been detected. Kirchhoff attacked this problem vigorously and obtained abundant results, finding nine terrestrial metals present in the solar atmosphere. Ångström and his collaborator, Thalèn, were occupied with similar inquiries.

About this time Mr. Lockyer's work on solar phenomena began. He applied to the examination of sun-spots and faculæ the device of throwing an image of the sun, or of any desired part of the sun, on the slit