Abraham. Theory of Electricity.

(M. Abraham. Theorie der Elektrizität. Zweiter Band. Elektromagnetische Theorie der Strahlung. Dritte Auflage, 1914. (Teubner)).

The third edition of the second volume of Abraham’s classical course has been greatly expanded and altered in comparison with the second. Some of these changes had already been foreshadowed by the reworking to which the fourth edition of the first volume, published in 1912, was subjected. Thus, for example, the theory of wireless telegraphy was transferred to the first volume and now, naturally, is absent from the second volume. The rearrangement of the chapter on the electrodynamics of moving bodies had been indicated by the transfer of this chapter to the first volume. But in addition to such and other minor changes and additions, natural for any new edition (new experimental data, references to the latest literature, etc.), in the third edition we find a large number of far more important changes and additions. These changes were prompted by the rapid development, in recent years, of the electrodynamics of moving bodies, in which, alongside Einstein, Minkowski, and other outstanding physicists, the author himself took a large part, as well as by the new major successes of electron theory. They found expression in a whole series of new paragraphs included in the book, and sometimes in a fundamental reworking of other paragraphs and even chapters. In view of the exceptional importance of the questions that have undergone new treatment and consideration—such as, for example, the magneton theory and the generalized principle of relativity—it seems, of course, desirable briefly to indicate the principal changes. The most important of them are the following.

In the chapter on the dynamics of electrons, § 23 deserves special attention; it sets forth the doctrine of the momentum of the energy flow and of its inertia, which the author justifies independently of the principle of relativity.

It should further be noted that in the second edition the rigorous theory of the vapor-like electron according to R. Hertz and A. Sommerfeld has now been omitted. Of great interest are §§ 25, 26, and 27, in which the theoretical foundations of the doctrine of magnetons are set out in detail, with special attention given to the radiation of such rotating systems of electrons. The relations derived in these paragraphs then served as the basis for the magneton theory of the magnetization of diamagnetic bodies, presented in § 31, as well as for the theories of paramagnetic bodies by Langevin and of ferromagnetic bodies by Weiss.

The chapter on the electrodynamics of moving bodies has undergone extensive revision. Here, in setting forth the interrelation of the fundamental equations of electrodynamics for moving bodies, given by E. Cohn, H. Lorentz, and H. Minkowski, the author has made use of the results of his own work on this question, published in the Rendiconti del circolo matematico del Palermo.

Finally, § 51, devoted to the exposition of the theory of the extraordinarily important question of the “weight” of energy, which is closely connected with the question of the nature of gravitation, is of special interest. In this paragraph the author gives a brief account of the generalized theories of relativity—the theories of the fundamental electrodynamic equations for bodies moving in the field of gravity. Abraham here considers both the theories of gravitation of Einstein and of the author, which reject the postulate of the constancy of the velocity of light, and the theories of G. Mie and G. Nordström, which seek to preserve this postulate and thus to remain on the basis of Einstein’s original principle of relativity.

Such are the principal changes introduced by Abraham into his book, giving it an unquestionably new and greater interest.

N. Papaleksi.