Energy Distribution in Spectra 1

Abstract

OUR knowledge of the structure of very fine spectrum lines is now on a secure and nearly comprehensive basis, from the points of view of both theory and of experiment, and it is very remarkable that so little is known of the distribution of energy in these lines, either in individual lines or as between the different lines contained in the spectrum of any atom. The analysis of the spectra of atoms, theoretically and in the laboratory, is now recognised as the most critical test to which any theory of atomic structure can be subjected, and we have recently had theories of the atom entirely based upon the wave-lengths of the radiations which they emit. A question of equal importance, to which I now wish to direct your attention, is the relative amounts of energy which the atom throws out in the form of radiation in the differentwave-lengths, for this is well known to vary in some cases very greatly according to the circumstances in which the atom is excited. I shall describe, in the first instance, a method designed by Dr. Merton for investigating the distribution of energy among spectrum lines, or in the breadth of an individual line, with great accuracy. It is possible by this means to obtain the long-desired object of an absolute scale of spectral intensity, independent of all the ordinary difficulties determined by such matters as the unequal behaviour of the photographic plate for light in different regions of the spectrum. Dr. Merton and I have been working together on this subject for the past three years, and I shall conclude the present lecture with an account of some of the more interesting results which have been reached, after an explanation of the method.