Bibliography

Course of Physics, Vol. 2, edited by Academician N. D. Papaleksi, OGIZ—State Publishing House of Technical-Theoretical Literature, 1947, 694 pp., 408 figs., with index.

This textbook appeared as the result of a revision of Michelson’s course of physics. Even in the last edition of Michelson’s course there remained no more than a fifth of the original text. The subsequent work on the course led the authors very far from that textbook, and thus an entirely new book arose.

The course of physics under review is intended to serve as a textbook in higher technical educational institutions and in the physics-and-mathematics faculties of universities, in the first and second years of study.

Unfortunately, it must be stated that, although the book market has been enriched by a generally useful book, the principal task—to compile a textbook for a course in general physics—has remained unresolved.

As in most cases when authorship belongs to several persons, the book under review suffers from considerable heterogeneity. The style of presentation in the sections “Electricity” (S. M. Rytov) and “Optics” (V. L. Levshin) is quite different. Whereas Levshin’s exposition, in its use of mathematical calculations and in its general direction, is sufficiently close to the character of lectures read in the first years, the part of the book written by Rytov is an introduction to the theory of the electromagnetic field, but in no way a course in electricity forming an integral part of a course in experimental physics.

The entire construction of this part—the style of exposition, the distribution of the material, the order in which concepts are introduced—corresponds to a course in the theory of the electromagnetic field, with small excursions into electron theory.

The difference from a textbook on the theory of the electromagnetic field (Tamm, Becker) consists only in the simplification of calculations, and where such simplification is impossible, in the presentation of the results of computations not actually carried out.

There is no doubt that students of physics-and-mathematics faculties studying theoretical physics will be grateful to the author and will read the chapters he has written with great benefit to themselves. But we fear that such gratitude the author will not receive from first-year students (to say nothing of those in higher technical institutions). In most higher technical institutions, by the time students listen to the course on electricity (second semester), they do not have the mathematical knowledge necessary for reading this book; but even if they do possess this knowledge (in university physics faculties), the abstractness of the exposition characteristic of theoretical physics will be a great obstacle for the beginning student studying physics for the first time.

In addition to all this, it should be remembered that students of higher technical institutions become acquainted with physics only in this course, while university students, in subsequent study, receive information only in specialized physics. Thus, from our point of view, it is quite wrong to teach a student in the first years of an educational institution only separate elements of physical theory. Physics is an experimental science, and one’s first acquaintance with it must be built—

...be based on experiment. Only after becoming acquainted, from experiment, with the emergence of the basic physical concepts will the student correctly assess the genesis, role, and place of physical theory.

The manner of exposition adopted in the part “Electricity” does not allow the author to explain, for example, in the chapter “Electrostatics,” how capacitance, induction, and the dielectric constant are measured. In the exposition of electromagnetic induction, a large (and, in general, very good) paragraph is devoted to explaining the fact that the work expended on the displacement of a conductor in a magnetic field is returned in the form of the work of the electromotive force of induction, but not a single line is devoted to the phenomenon of electromagnetic induction as a means of measuring the quantity of electricity. Not a word is said about how magnetic permeability is measured. Further examples need not be given, since from what has been said it is quite clear that the author did not consider it necessary to set forth the elements of experimental physics, to explain the experimental origin of particular concepts, or to show the emergence of theory from experience.

No matter what simple things the author may present, the theoretical character of the exposition dominates over them. Here is a characteristic example. In presenting elementary electron theory of conductivity, one may, as is well known, show that Ohm’s law will hold only if it is assumed that the thermal velocities of the electrons are much greater than the velocity of ordered motion. The author presents this as follows: on p. 93 it is said that the thermal velocities of the electrons have such-and-such an order of magnitude. Where this is known from is not stated; nevertheless it may be understood, since we are dealing with a quantity not directly measured. Then on p. 100 it is said: as we indicated above, the thermal velocity is much greater than the velocity of ordered motion; consequently, we arrive at such-and-such a formula, which is Ohm’s law. This is, of course, a minor point, but a very characteristic one: precisely this is the style of exposition—first a hypothesis is introduced, and then facts are derived from it. It seems to us that the reverse course of exposition is more appropriate for a general course of physics—the consideration of facts in order to show how theory is born on their basis.

Even without disputing with the author about the character of the presentation of the material, several remarks may be made concerning the section on electromagnetism. Among the awkward points one may include the fact that the magnetic field in a vacuum is first presented, and only afterward is the medium introduced. The impression may arise, for example, that the formula for the elementary intensity of a magnetic field is valid only for a vacuum. The following will also remain unclear: if the intensity of the magnetic field is determined by the rotational moment acting on the frame with current, then why is there no experimental coefficient of proportionality in the Biot–Savart formula, which relates already previously determined quantities? The connection between these two formulas ought to have been shown. The paragraph on the ponderomotive (whether this word is needed at all, by the way) interaction of current elements is wholly superfluous; it considers a case that has no significance either for theory or, still less, for experiment, and illustrates the generally incorrect idea that, for forces, the equality of action and reaction may fail to hold. The complete neglect of the practical system of electrical units is certainly inadmissible. Even in the special section devoted to systems of units, nothing is said about the fact that in practical electrical engineering the coefficient 4π is introduced into other formulas, that by lines of force in this system only lines of electrostatic induction are meant. The values of the dielectric constant and magnetic permeability of vacuum are not given. One should nevertheless make it easier for the student to read the enormous literature on theoretical electrical engineering.

Our criticism of this part of the book is criticism of a textbook of physics for the first years of universities and higher technical schools. If one forgets the purpose of the book, the impression will be quite good. As an introduction to theoretical physics, the chapters we have...

These sections, written by Rytov, leave something to be desired. One may note a number of especially successful paragraphs, for example alternating current in an unclosed circuit, the electric field of a steady current outside conductors, and many others. Consistency in the presentation of the theory, rigor without excessive formalism—all these are undoubted merits of this part of the book.

The exposition of optics has, as was already indicated at the beginning of the review, an entirely different character (this part also includes the chapter on the structure of the atom, written by E. L. Feinberg). Most of the chapter is devoted to a description of the essence of the experiments in this field, the calculation of these experiments, and the presentation of theoretical views on the subject. The authors use a very modest mathematical apparatus and do not set themselves the task of a systematic exposition of the theory of the question. After a brief introduction, questions of observation and calculation of interference curves are considered. Next the simplest cases of diffraction by a Fresnel and a Fraunhofer aperture are described (the formulas for the intensity distribution are not derived). Diffraction of X-rays is considered here as well. In this paragraph the space lattice is for some reason called a volume lattice. The Debye diagrams shown in the figure are unpleasantly striking in their poor execution, their appearance being quite inconsistent with the instructions of the text (p. 388). Further, geometrical optics and the construction of optical instruments are set out in detail. A short chapter is devoted to resolving power. After a generally customary textbook presentation of the questions of dispersion and polarization, as well as a chapter on the optics of moving media (S. M. Rytov), there follows a chapter devoted to quantum phenomena. Here it is shown very well and clearly why wave conceptions of the nature of light are insufficient (using the Compton effect and the inertia-free character of the photoelectric effect as examples). The principal experiments proving the quantum nature of light are perhaps described somewhat too briefly. In the chapter, the impossibility of a vulgar interpretation of light quanta as “little balls” is carefully emphasized.

In considering the questions of light emission and the structure of the atom, the authors refrain from analyzing the systematics and nomenclature of spectral terms. This seems to us entirely correct, since this part of the doctrine of light is mastered only in practical work, while memorizing this systematics gives nothing toward understanding the foundations of physics. At the same time, the main thing has been done: namely, the concept of the energy levels of the atom is explained in detail, and their discreteness is demonstrated through the description of experiments. These sections contain many interesting and memorable experimental data on the questions of luminescence and absorption spectra.

In the chapter on the structure of the atom, as well as in the chapter devoted to quantum optics, special attention is paid to showing the reasons for the impossibility of classical theory. It is also shown why the planetary model of the atom is impossible.

In § 3, when considering the formation of an electron diffraction pattern, it is persistently emphasized that the wave properties of the electron, like those of a quantum of light, are connected with a statistical understanding of the process. In our view, the author has quite successfully managed to explain the fundamental basis of quantum mechanics. It is shown with sufficient clarity that the essence of the uncertainty principle “lies not in the limitation of our knowledge, but in the complex properties of the electron itself.”

In the last part—“Physics of the Atomic Nucleus” (L. V. Groshev)—in a scope and style fully corresponding to a university course in physics, the questions of radioactivity and the artificial transformation of elements are presented.

A. I. Kitaigorodskii