Bibliography

Nasledov, D. N. Lecture Notes on Physics (Optics and Atomic Structure). Published by the Military Red Banner Budyonny Academy of Communications. Leningrad, 1947, 180 pp., 106 figures.

The title of the book is in keeping with its content. The book indeed contains material whose scope does not exceed what can be presented in 15–17 lectures assigned, under existing programs, to optics and atomic structure in the general physics course at technical educational institutions.

The need for this kind of textbook is beyond doubt. Alongside textbooks, detailed accounts, and detailed presentations of the subject, the student should have at hand a book in which the material presented to him in lectures is set out concisely and clearly, and is in principle sufficient for mastering the course being taught. Optics and atomic structure usually make up one quarter of the general physics course. In this book they occupy 11 printer’s sheets. It would be highly desirable to create a physics course of 40–45 sheets in length. We do not have such a course, and therefore the book under review is of special interest.

The book consists of 13 chapters, to a sequential consideration of which we now turn. The first, introductory chapter sets forth Newton’s corpuscular theory of light, Huygens’ mechanical wave theory, and the electromagnetic theory of light. At this point the account of the nature of light for some reason breaks off. It seems obvious to us that the time has long since come not to single out quantum ideas about light as a special novelty at the end of the book. If the author considered it expedient to preface optics with a historical survey of the nature of light, then he should have carried it through to the end.

Further, in the introductory chapter there is a paragraph on the classification of waves and on the measurement of the speed of light. A very essential element is lacking in this introductory chapter: a strictly experimental definition of concepts. A general physics course can be taught in a technical higher educational institution only as a course in experimental physics. It would be an unquestionable mistake to construct it as a simplified course in theoretical physics. Therefore the task of the lecturer and the author of a textbook is, from our point of view, to show the necessity of introducing one or another concept directly from experiment. This is especially important for modern optics, which operates alternately with the concepts of wave and quantum. Therefore, at the very beginning of the optics course, one should show the experimental meaning of the concepts “wavelength,” “wave intensity,” and “spectrum,” explaining that different theoretical content may be put into these concepts depending on the language—quantum or wave—in which we describe the phenomenon.

In the second chapter, “Reflection and Refraction of Light,” the geometric laws of reflection and refraction of light are given without any analytical or geometric proof. As their consequences, likewise only from the geometric side, the phenomena of total internal reflection, the path of rays in a plate, a prism, and a thin prism are considered. The last paragraph describes the construction of Abbe and Pulfrich refractometers.

The exposition of the material in this chapter raises a decisive objection. Why should a student of a four- or, at the very least, three-semester course not know the questions of reflection and refraction of light? In the very same space, by throwing out the material taught in secondary school, it would have been possible to give not a description but an explanation of these phenomena. It is not at all difficult to speak about investigations of total internal reflection or about measurements of the coefficients of reflection and transmission of light that lead to confirmation of Fresnel’s formula.

In the third chapter the dispersion of light is likewise presented formally and descriptively. No attempt is made to approach, either from the theoretical side or from the experimental side, the resonant nature of absorption. At the same time, almost half of this small chapter is devoted to the tedious algebraic derivation of the group-velocity formula. The other half of the chapter contains the most elementary information presented in the secondary-school course.

The following chapter, entitled “Geometrical Optics,” sets out in full school material, namely the geometry of reflection from a plane and spherical mirror, as well as the geometry of a lens and of a system of lenses. This is quite excessive, especially since these questions do not even figure in the programs approved by the Ministry of Higher Education.

The chapter on the interference of light is more successful. The concept of optical length is well explained, as are Fresnel’s experiments. In the exposition of interference from a plate there is no explanation (even an energetic one) of the loss of a half-wave upon reflection. The question of the causes of interference coloration is passed over in silence.

A whole series of the most important concepts is also absent from the following chapter on the diffraction of light. No theory of the diffraction grating is given, and therefore there is no resolving power of the grating. At the same time, Cornu’s construction is set out in detail. Nothing is said either about the resolving power of optical instruments. One should not think that the author avoids the exposition of these questions, considering them too difficult, since the diffraction of Fresnel, as well as Fraunhofer diffraction from a slit, are considered by him in great detail. Thus, in our opinion, the selection of material for this chapter is very unsuccessful.

The phenomena of the polarization of light are also considered very formally and, what is necessary, quite popularly. The causes of double refraction, indicated in one paragraph, are explained quite inadequately. The phenomena of circular and elliptical polarization are not considered at all. However, here the reviewer does not take it upon himself to assert boldly that the treatment of these questions in a course of general physics is necessary.

In Chapter 8, under the title “Thermal Radiation,” the concepts of emissivity and absorptivity of a body are defined, the exponential law of absorption is derived, and the practical construction of an absolutely black body is explained (incidentally, here it would not have been superfluous to mention the name of Prof. Michelson along with the names of Lummer and Pringsheim). As empirical laws, the laws of Kirchhoff, Stefan, and Wien are formulated. In the last paragraph, as is usually done, the necessity of introducing the quantum hypothesis is discussed. Planck’s formula is given. For some reason it is not even said that Stefan’s and Wien’s laws are consequences of this formula.

The author then turns to the question of the structure of the atom. The experimental basis of Rutherford’s model is well explained, and the necessity of abandoning classical ideas when considering the radiation of the atom is also clearly shown. Next the Bohr theory of the hydrogen atom and the Franck and Hertz experiments are considered. No modern conception of the atom is given. It seems to us absolutely necessary to give the reader an idea of the conventional nature of the concept “orbit of the atom.” The author has not done this, as a result of which the student will receive an oversimplified, to the point of distortion, picture of atomic structure.

In the chapter on X-rays, perhaps the most essential material for this field of knowledge has been selected. It might have been appropriate to dwell in somewhat greater detail on the applications of X-rays (although in a course on X-rays one need not raise the question of the refraction of X-rays). The derivation of Bragg’s formula is well given (one may note, however, that it would not have been superfluous to mention Wulff’s name in connection with this formula).

Chapter 11 is devoted to quantum phenomena. The photoelectric effect is set forth in sufficient detail, while the questions of fluorescence are treated briefly. A detailed algebraic derivation of the formula for the Compton effect is quite needlessly given. The main idea of this effect—the fact that in this experiment the necessity of ascribing a definite momentum to the quantum emerges clearly—is not emphasized sufficiently. Next, the question of the pressure of light is briefly presented. There is no account of Lebedev’s experiments. The Doppler effect is presented specifically in order to show the applicability of quantum theory in cases where wave theory leads to good results. Is this worthwhile?

Chapter 12 discusses the wave properties of the electron. The first paragraph of this chapter, in which geometrical electron optics is presented, is successful. From this a transition to the phenomena of electron diffraction is made quite naturally.

In Chapters 11 and 12, the student should have been given a clear notion of the essence of modern ideas about the motion of matter, and the inadequacy of the language borrowed from descriptions of motions visible to the eye for explaining the motion of elementary particles should have been shown. Instead, the author emphasizes the dualistic behavior of particles. The student inevitably gets the impression that there exist two theories, both of them imperfect. The term “dualism” should in general have been discarded from these chapters.

In the last, 13th, chapter, all the most essential information from the physics of the atomic nucleus is presented. This chapter is successful.

The chief shortcomings of the course under review are, as follows from what has been said above, the excessive elementary character of the exposition, the repetition of school material, and the absence of explanations of certain quite fundamental concepts (for example, resolving power). Despite the elementary character of the exposition, the course is nevertheless constructed as a simplified presentation of theoretical physics, not as an experimental course. There is no doubt that all these shortcomings could have been eliminated without increasing the volume. The merits of the book are its simple and clear language and the absence of errors.

A. I. Kitaigorodsky