Notes

Abstract

ON Monday last, October 31, twenty-live years had elapsed since Prof. P. Zeeman's first observations of the decomposition of spectral lines by a magnetic field were communicated to the Amsterdam Academy of Sciences in a paper that appeared shortly afterwards in the Philosophical Magazine under the title “On the Influence of Magnetism on the Nature of the Light emitted by a Substance.” By this important advance in magneto-optics, the first made since the days of Faraday and Kerr, a new and vast field of research of uncommon interest was opened. In commemoration of this development a reprint of Prof. Zeeman's original papers has now been published by the physicists of the Netherlands, conjointly with many scientific men of other countries. Prof. Zeeman has also been honoured by a special issue of the Dutch journal Physica, containing contributions by C. Cotton, G. E. Hale, Ph. Kohnstamm, T. van Lohnizen, H. A. Lorentz, A. van Maanen, E. E. Mogendorff, H. Kamerlingh Onnes, F. Paschen, and C. Runge. Some of these articles are devoted to an appreciation of Zeeman and his work or to the history of his discovery. In others the present state of magneto-optical theory and the latest results in the experimental investigation of the Zeeman effect are discussed. The bearing of the phenomenon on solar physics and the conclusions that have already been drawn concerning the magnetic field of sun-spots and the sun's general magnetic field are explained by Prof. Hale and Mr. van Maanen. Finally, Prof. Paschen describes a new phenomenon lately discovered by him, and consisting in the appearance, under the influence of a magnetic field, of certain spectral lines that cannot otherwise be produced. We are glad to avail ourselves of this opportunity of expressing our high appreciation of Prof. Zeeman's brilliant work, by which he has contributed most effectively to the development of modern physics.