A. A. EIKHENVALD. Electricity. Revised and enlarged edition, GIZ, Moscow—Leningrad, 1927, pp. VIII + 758, price in binding 8 rubles.

The well-known course by A. A. Eikhenvald has appeared in a new, fourth edition. The book has been greatly enlarged in that part which treats of new phenomena, partly discovered and partly attracting special attention during the last decade.

The last 200 pages have been written almost anew, even externally set apart as a special, third part, bearing the title “Electrons.” And credit must be given to the author: with his characteristic mastery he has managed, over the course of these two hundred pages, to present an enormous amount of experimental and theoretical material with extraordinary clarity, simplicity, and sufficient completeness.

The special difficulties connected with the exposition of questions of this kind consist, as is well known, in the necessity of touching upon a subject in which the most diverse “branches” of physics are intertwined. A. A. Eikhenvald has resolved this difficulty by introducing into the text a brief exposition of all the information from molecular physics, optics, etc., necessary for understanding the matter. The device is simple in conception, but requires from the author exceptional pedagogical talent, since one has to steer between the Scylla of incomprehensibility and the Charybdis of boundless swelling of the book. A. A. Eikhenvald has safely guided his ship through and has produced, in 758 pages, a textbook excellent in completeness and intelligibility.

It would be superfluous to enumerate all the numerous additions and supplements that have entered into the 4th edition of the book under review. I should like only to dwell briefly on the plan of exposition, which in its essential features has remained the same as in the previous editions. The first two parts (530 pages) are devoted to an exposition of material that might be called formal. Only the last 200 pages contain those modern “electronic” ideas which pour concrete content into these “forms.”

Of course, such an exposition has its advantages. On the basis of conceptions still only in the process of formation, it would hardly be possible to set forth, with such completeness and orderliness, the whole aggregate of information as the formal theory of the electric field permits. But, on the other hand, electronic ideas have to such a degree become an organic part of modern physics that it is hardly desirable to postpone acquaintance with them until the end of the course.

And perhaps the finished orderliness of formal electrostatics and magnetostatics does not mean so very much for the second-year student, whom A. A. Eikhenvald’s book will primarily serve. From this point of view, an exposition not so orderly, but operating from the very beginning with the electron as a physical reality, could probably yield no smaller, and perhaps even greater, results.

As regards particular passages in the book, I should like to draw attention to only two points.

The first point concerns the electromagnetic character of the mass of the electron (pp. 638 and 692). But should this point be used to elucidate the electromagnetic character of mass in general? In any case, since the law of variation of mass with velocity is a general law, Kaufmann’s experiments cannot serve as proof that the electron is “pure electricity.”

The second passage concerns the clarification of the concept of two systems of units (pp. 218 and 294). This point is often difficult for students. And it seems to me that it should have been emphasized with greater clarity that at the basis of electrical

of the system lies Coulomb’s first law, while at the basis of the particle system lies Coulomb’s second law, whereas the Biot–Savart law is only the point of meeting of the two systems: it makes it possible to determine the electrical unit of magnetism if we already have at our disposal an electrical unit of current, or to serve for determining the magnetic unit of current if the magnetic unit of magnetism has already been established.

The appearance of the book is extraordinarily pleasant. The paper, type, and figures are very good. Misprints are quite unnoticeable. Only in the table of chemical elements, hafnium (72) has accidentally fallen into the cell of the rare earths and, moreover, has retained there the obsolete name Tu II, although in the main table it is called Hf.

Gr. Landsberg.