Bibliography

KARL FÖRSTERLING. Lehrbuch der Optik, pp. XII + 610. S. Hirzel, Leipzig, 1928; price: 40 marks.

K. Försterling. Textbook of Optics.

A new, large, modern course in optics, written by an outstanding specialist in this field, is a long-awaited event in the physics literature. In recent decades so much that is new has been discovered in the science of light that it is impossible to make do with a simple, somewhat updated reissue of earlier excellent books on optics. The mechanical addition of several new chapters (as was done, for example, in the new edition of Schuster’s book) disrupts the style of the book and is in general a device hardly suitable for a textbook. What is needed is a new book, written entirely in the new era. The state of the theory of light, however, is still such that there is no possibility of arranging coherently and illuminating theoretically from a single point of view even the principal experimental material. The fusion of classical and quantum optics into a single integral doctrine of light is a task for the future; for the time being, the experimental data have to be classified not so much according to theoretical as according to empirical logic. It could have been expected in advance that the book under review would to a considerable extent lose the coherence and completeness that characterized books on light in the good old days. The author does not succeed in smoothing over the sharp break in the transition from the first part to the second, from wave optics to the theory of spectra. At the same time, however, the textbook character of the book is fully maintained. It is not a monograph and not a handbook, but a very valuable aid for a person beginning the serious study of optics. The calculations are carried out in great detail and present no difficulties for a reader who studies the book attentively. The text provides all necessary auxiliary information; in separate chapters the theory of Maxwell and the electron theory are set forth with sufficient completeness. The doctrine of quanta (including a very detailed exposition of Schrödinger’s theory) is the subject of the most extensive chapter of the book, comprising more than 100 pages. At the end of the text three special appendices are given: I. Voigt’s theory of the complex Zeeman effect. II. Maxwell’s equations in curvilinear coordinates (for the solution of diffraction problems). III. The canonical form of Lagrange’s equations. The chapter

on geometrical optics and the theory of optical instruments is quite appropriately separated from the main text and placed at the end. A textbook of optics may pursue three aims: 1) an exposition of the present state of the doctrine of light, 2) acquainting the reader with the theoretical and mathematical methods of this field, and 3) acquainting him with the distinctive experimental techniques and methods of optics. Försterling strives, to a certain extent, to satisfy all three requirements, but gives preference to the second. In this one may see either a merit or, conversely, a shortcoming of the book (if one takes into account the fundamental imperfection of the contemporary “theory” of light), but in any case the reader must bear this in mind when turning to the new textbook. In experimental terms it will not replace Wood’s famous book. As an exposition of the modern doctrine of light, Försterling has very many gaps. The book does not touch at all upon X-ray optics; it ruthlessly compresses (to a few pages!) the whole extensive section on the actions of light (light pressure, resonance radiation, fluorescence, the photoelectric effect); there is no mention at all of photochemical processes. There is no theory of molecular spectra; no idea is given of the classification of atomic spectra and of modern spectral notation (which would have been especially desirable in a modern textbook). There is no chapter at all on the scattering of light. The experimental data are insufficient, and sometimes overly schematized. The author, of course, knows these gaps in his book and points to many of them in the preface. They are caused by the need to combine the character of a textbook of acceptable length with a detailed exposition of mathematical theory, diffraction, crystal-optical phenomena, etc. In the classical part of the book Försterling often relies on the exposition of Drude and Focht. For pedagogical reasons, the phenomena of the optics of moving media are interpreted on the basis of Lorentz’s theory, and the principle of relativity is set forth very briefly. Thus the merits of Försterling’s book are its modernity and didactic character; its inevitable shortcoming is incompleteness. In any case, we now have a textbook by which modern optics can be studied at least “three quarters” of the way.

S. Vavilov.