Atomes et électrons. Rapports et discussions du Conseil de Physique tenu à Bruxelles du 1-er au 6 avril 1921 sous les auspices de l’Institut international de Physique Solvay. Paris. Gauthier Villars. 1923 VIII + 271 p.

Atoms and Electrons. Reports and discussions at the 3rd Physics Congress of the Solvay Institute.

In the physics congresses in Brussels, convened at the initiative of Solvay, there has apparently been found a fully rational solution to the difficulty with which scientific congresses are increasingly burdened from year to year. The growing number of scientific workers and the progressive differentiation of fields of research bring with them an enormous number of congress participants and a commensurately enormous number of papers. The latter are willy-nilly squeezed into 5–10-minute periods, pass without discussion, and appear in proper form only in journals—the congresses become to a considerable extent useless. The structure of the Solvay congresses is entirely different. First of all, these are congresses for

a definite topic, which is the main axis in the present development of physics (1st congress: theory of radiation and quanta; 2nd—structure of matter). Further, the number of members of the congress is extremely limited; only the authors of the most outstanding investigations in the given field take part in the congress. The content of the papers is, as far as possible, sent out in advance to those who desire it; the papers are compiled beforehand and preliminarily distributed to the participants for acquaintance. The center of gravity falls on the discussion of the papers. It is quite obvious that the results of the work of such a meeting must be exceptionally valuable; a living, direct art of outstanding specialists, of course, cannot be replaced by any printed polemic.

The president of the 3rd congress was H. A. Lorentz; members: Barkla, Bragg, Brillouin, de Broglie, Mme Curie, Ehrenfest, de Haas, Kamerlingh Onnes, Knudsen, Langevin, Larmor, Millikan, Perrin, Richardson, Rutherford, Siegbahn, F. A. Lindemann, Weiss, and Zeeman. In addition, Michelson was present as a guest at the congress.

The papers heard at the congress are the following: Lorentz.—Remarks on the new electronic theory; Rutherford.—Structure of the atom; de Broglie.—The relation \(h\nu=\varepsilon\) in photoelectric phenomena; Kamerlingh Onnes.—Paramagnetism at low temperatures; superconductors and the model of the Bohr–Rutherford atom; Bragg.—Intensity of reflection of X-rays by diamond; de Haas.—Moment of quantity of motion in a magnetic body; Bohr.—Application of the theory of quanta to atomic problems; Ehrenfest.—The correspondence principle.

Some of the papers, by the time they appeared in print, had already become somewhat obsolete (for example, the paper of Bohr and Rutherford). The chief interest of the book, however, lies not in the papers themselves, but in the discussions concerning them. These discussions occupy almost half the book; especially extensive debates took place after de Broglie’s paper. Millikan very skillfully divided his report on his numerous works in various fields over the past years in the form of special remarks during the discussions. It is, of course, not possible in a review to set forth the debates, which quickly pass from topic to topic. We shall note only a number of Langevin’s remarks concerning many papers (pp. 126, 127, 256, and others), brilliantly emphasizing a characteristic feature of the view expounded (for example, the correspondence principle) or else approaching the subject from a new, unexpected side (a thermodynamic interpretation of Millikan’s results). Larmor, noting the difficulties of the electronic theory in connection with Lorentz’s paper, makes the following remark, recalling the existence of an important unresolved problem: “If electricity can be explained by electrons, then the electron itself, in the final analysis, is not explained by electricity.”

It should be regretted that, in the first edition as well, German scholars could not take part: all the fundamental questions connected with the theory of quanta, raised and illuminated in the reports, had their origin precisely in Germany.

The absence of a subject index is also, unfortunately, a shortcoming of the book under review for purposes of rapid reference.

O. Vavilov.