Physics in the USSR

1917–1937

E. V. Shpolsky, Moscow

The Great October Revolution opened a new epoch in the development of science in the USSR, and physics belongs among those sciences for which the historical date of October 1917 is especially significant. Indeed, looking back at the development of physics in Russia, it is not difficult to see that the contribution made by Russian physicists to the development of their science before 1917 was very modest. The reason for this, of course, lay not in a lack of talents—the many-millioned mass of the peoples of the USSR always had enough of them—but in the cultural and technical backwardness of old Russia. It would be difficult to write the history of physics in Russia before the second half of the nineteenth century, since the most important thing was absent: continuity. Therefore, even if a genius arose from the depths of the popular masses, as, for example, Lomonosov did, he remained unrecognized and isolated; in his own country he had neither predecessors nor immediate successors. If, on the other hand, a major scientist was invited from the West, he likewise found no soil for himself in Russia and continued to work for the West. It is enough to recall that Euler was a member of the Petersburg Academy, but his works, widely used abroad, found no response in Russia.

During the nineteenth century one can point to a few names of major scientists who enriched physics with valuable works or discoveries. Vasily Petrov, professor of the Medical-Surgical Academy in Saint Petersburg, who built “in a different way an enormous voltaic battery,” invented the voltaic arc in 1803. But this discovery remained little known, and historical tradition connected it with another name—H. Davy—who, independently of Petrov, built a voltaic arc. A. G. Stoletov is credited with exemplary investigations of the photoelectric effect, which played a major role in clarifying the nature of this important phenomenon. A. S. Popov, in 1899, somewhat earlier than Marconi, was the first to carry out radiotelegraphy between Petersburg and Kronstadt, but this discovery, just like the discovery of Vasily Petrov in its time, remained unnoticed and was not used. Raz—

it is; these three names do not exhaust all of nineteenth-century Russian physics, but it would be difficult to add many names to them (one may mention Golitsyn, Avenarius, and Lenz).

This weak development of physics in nineteenth-century Russia was no accident. Physics there had no soil of its own. The meager technology and industry of pre-revolutionary Russia, to a significant degree in the hands of foreign capitalists or of poorly cultured Russian merchants, did not need its own physics as a basis for development. The advanced physicist in Russia was terribly isolated; he had no milieu, and, in the end, he did not have sufficient means for developing his work. That is why, even at the beginning of the twentieth century, when a noticeable revival in the field of physics began to appear, in Russia there was almost no one from whom to learn, and the majority of the major physicists of pre-revolutionary Russia (Lebedev, Michelson, Goldhammer) received their scientific education abroad.

A certain turn, as has been said, began to take shape only in the twentieth century. In Petersburg, Moscow, Odessa, and several other cities, university physics institutes were built according to the European model. A number of major scientists (Umov, Lebedev, Eichenwald, Goldhammer, Kolla) occupied university chairs. Special credit for the development of pre-revolutionary physics in Russia belongs to P. N. Lebedev, who not only enriched science with his own classic works, but also for the first time created in Moscow a genuine scientific laboratory. From his school came a number of scientists, many of whom are known throughout the Union (P. P. Lazarev, T. P. Kravets, V. K. Arkadiev, A. K. Timiryazev, V. I. Romanov, N. N. Andreev, A. B. Mlodzeevskii, V. D. Zernov).

At the same time, in the Petersburg of that period, there appeared a number of brilliant scientists (A. F. Ioffe, D. S. Rozhdestvenskii, P. S. Ehrenfest), who brought a strong revival into the stagnant scientific atmosphere of bureaucratic Petersburg.

Development of the Network of Scientific Research Institutes

A characteristic feature of the development of physics before the revolution was that physics was a university science. Individual physicists and entire laboratories were directly connected either with universities or—in rarer cases—with technical higher schools (for example, the well-known works of A. A. Eichenwald were carried out in the laboratory of the Moscow Engineering School). Such, for the most part, was the path of the development of physics abroad as well.

Such an organization of scientific work, along with certain advantages, also has very substantial shortcomings. If earlier, in the nineteenth century, a physicist could work in the modest laboratory of a higher school, then at the present time, for work in most areas of physics, the setting up of experiments at a very high technical level and often on such a large scale is required that it is not feasible for the laboratories of a higher school.

It suffices to recall work in the field of nuclear physics, where experimental installations often require special buildings, or the work of P. L. Kapitsa with strong magnetic fields, the organization of which required very considerable funds and extensive premises. In addition, a physicist-professor usually has a considerable load in the form of lectures and examinations—a load which for many outstanding scientists was burdensome. That is why, even before the revolution, the idea arose of creating special scientific-research institutes of physics not connected with higher education.

P. N. Lebedev, who in 1911 was forced to leave the university as a result of its being broken up by the minister of public education, wrote on this subject: “Large physical laboratories intended exclusively for scientific research have long existed in the West—in England, Germany, and America. Steadily working out scientific problems, they, as experience has shown, enrich technology in a completely unexpected way.... Unfortunately, we still have no such national physical laboratory, but both the need for it and the necessary scientific forces are present. That is why Russian society should take care to create such a laboratory, having first discussed the size and character of this new institution” (P. N. Lebedev, Collected Works, Moscow, 1913, pp. 353–354).

However, the tsarist government did not respond to this appeal in any way, and only through public initiative was the “Moscow Society for a Scientific Institute” created, and with the private donations collected the organization in Moscow of a research institute of physics was begun.

Unfortunately, P. N. Lebedev, who died in 1912, did not see this institute, and after leaving the university he was forced to work in the modest laboratory of the Shanyavsky Municipal University.

From the very beginning of the revolution the organization of scientific-research institutes of physics was undertaken on a broad scale. In 1918, at the height of the struggle against counterrevolution and intervention, amid the numerous economic difficulties inherited by the revolution from the world imperialist war and the tsarist government, the largest institutes were created, which quickly raised scientific work in physics to an entirely different level. With the support of the People’s Commissariat of Health, in 1918 P. P. Lazarev organized in Moscow the Institute of Physics and Biophysics. This institute conducted extensive work in various fields of physics (molecular physics, acoustics, photochemistry), biophysics (physiology of the sense organs), and geophysics. At approximately the same time two major institutes were founded in Leningrad: the X-ray and the Optical. The first institute from the very beginning had two large departments: medical-biological (M. I. Nemenov) and physical-technical (A. F. Ioffe). As the institute developed, these departments became less and less connected, and, in the end, from

from the physico-technical X-ray department there grew a powerful Physico-Technical Institute, which played an outstanding role in the development of Soviet physics. The Optical Institute, founded by a small group of enthusiasts of scientific and applied optics headed by D. S. Rozhdestvenskii and, at the beginning of its existence, of modest size, quickly grew into the largest institute in the world, enriching science with many most important investigations, and the economy of our country with valuable practical achievements. Alongside these institutes there arose a special institute for the study of radium—the State Radium Institute—and an entire system of so-called branch scientific-technical institutes, which are often, in essence, institutes of technical physics. Some of them (for example, the All-Union Electrotechnical Institute), like the Optical Institute, are the foremost in the world in their scale and richness of equipment.

The system of physical and physico-technical institutes experienced especially rapid growth from the beginning of the first five-year plan. The extraordinarily increased demands of socialist technology, the attention and care of the Party and the government—all this created exceptionally favorable conditions for the development of physics in the USSR. It was precisely in this period that, alongside the Leningrad Physico-Technical Institute, a whole network of physico-technical institutes and hundreds of factory laboratories was created. Large institutes were established in Tomsk (the Siberian Physico-Technical Institute), in Kharkov (the Ukrainian Physico-Technical Institute), in Dnepropetrovsk, and in Sverdlovsk.

Some of these institutes quickly grew into powerful and richly equipped scientific research institutions. Thus, for example, the Ukrainian Physico-Technical Institute established a number of excellent laboratories, namely: a laboratory for the study of nuclear processes, a low-temperature laboratory, and a laboratory of electrical oscillations. The Leningrad Physico-Technical Institute itself in 1932 spun off from itself a new large institute—the Institute of Chemical Physics. Alongside this, university physics institutes in Moscow and Leningrad developed into independent large research institutes; in Kiev, under the Ukrainian Academy of Sciences, a Research Institute of Physics was created.

With the transfer of the All-Union Academy of Sciences from Leningrad to Moscow, the small Physics Institute of the Academy of Sciences of the USSR turned into a major scientific center for theoretical work in physics. Finally, quite recently, under the same Academy of Sciences there was created a specially equipped Institute of Physical Problems, where P. L. Kapitsa continues his investigations in the field of intense magnetic fields and low temperatures—investigations that have brought him worldwide fame. Designed for a small number of scientific workers, this institute is brilliantly equipped and provides its workers with unlimited opportunities in setting up investigations1

As a result, by the twentieth anniversary of the revolution, we have a ramified network of physical, physico-technical, and branch technical institutes, and an entire army of scientific workers engaged in them in the study of the manifold problems of theoretical and applied physics. The decree of the Party and the government of June 23, 1936, opens new possibilities for the development of scientific work, and for higher-education departments, which must join the ranks of scientific-research institutions. Expenditures on scientific-research work in all specialties reach a billion rubles, and of these a considerable share goes to work in physics, which belongs among the most “expensive” sciences.

General Characterization of the Results Obtained

To give a complete survey of all the results obtained by Soviet physicists in a single article written by one author is an impossible task. Without striving for exhaustive completeness, we shall attempt to characterize the most essential results that have already entered into the common stock of world science.

The basic problem of modern physics—the problem of the structure of matter—has been widely and intensively developed by Soviet physicists. The period from 1917 to the present is characterized by a brilliant development of the theory of atomic structure. In this development, especially in its later stages, after the creation of the new quantum mechanics, Soviet theoretical physicists took an active and fruitful part. Here, first of all, it is necessary to note the works concerning various problems of quantum mechanics. As is known, Schrödinger’s equation for many bodies in principle makes it possible to calculate the structure of any atom, whatever the number of its electrons. However, as the number of electrons increases, the problem very quickly becomes mathematically so complex that its exact solution is impossible. To illustrate this complexity, it is enough to recall the example given by V. A. Fock: to find the energy levels of a sodium atom containing 11 electrons, it is necessary to find 2048 functions, each of 33 variables; and for a copper atom with 29 electrons it is necessary to seek already more than half a billion functions, each of 87 variables. It is clear that this is a practically insoluble problem. V. A. Fock developed approximate methods that make it possible to solve such problems sufficiently rapidly and with entirely satisfactory accuracy. Fock’s first method, representing a significant improvement of the method proposed by Hartree, is at present an indispensable tool for all theoretical physicists engaged in calculating the structure of the electronic shell of the atom. By means of this method, V. A. Fock’s collaborators at the State Optical Institute calculated the atoms of lithium (3 electrons) and sodium (11 electrons), the computed values differing from

experimental ones by only 1–2%. Fock’s second method, based on the symmetry of hydrogen-like atoms, gives somewhat less accurate results, but is distinguished by remarkable elegance and considerably shortens the calculations. By this method the atoms of sodium, aluminum, copper, and zinc have already been calculated.

Of great importance are V. A. Fock’s works in the field of quantum electrodynamics. Starting from the idea that every interaction between particles occurs not directly, by way of “action at a distance,” but through the interaction of these particles with the surrounding field, i.e., with light quanta, Fock constructed a very general theory that includes quantum mechanics proper, i.e., the laws of interaction of electrons and nuclei, as well as the laws of interaction of charged particles with light quanta, i.e., the theory of radiation.

Perhaps the most curious thing is that the ordinary Coulomb electrostatic forces are also obtained automatically from this theory. If one recalls that the theory is based on the idea that every interaction occurs exclusively through the surrounding field, then one may say that, in accordance with the spirit of modern physics, electrostatic interactions in this theory are regarded not as forces of “action at a distance,” but as forces of “action at close range.” Thus one may say that Fock’s theory is a modernized theory of “action at close range,” embracing a broad range of very diverse phenomena.

To the same circle of general problems of modern physics belong the works of L. D. Landau, published by him jointly with R. Peierls. In these works a profound analysis is given of such concepts as “measurement” in quantum mechanics, and those changes are outlined to which the customary elementary concepts of physics will have to be subjected in the future relativistic theory of quanta.

Quantum mechanics deals not only with general fundamental problems of physical science and not only with questions connected with the structure of the electron shells of atoms and molecules. It has proved extraordinarily fruitful in application to the most diverse physical phenomena. And in this direction Soviet physicists have done much. We shall give here only a few characteristic examples. As is well known, one of the first applications of quantum mechanics was to the theory of the electrical properties of metals. Ya. I. Frenkel was the first to give a wave-mechanical theory of the electrical resistance of metals. A number of works by I. E. Tamm were also devoted to the theory of metals; he also gave a theory of photoelectric phenomena.

Another example of the fruitful application of the methods of quantum mechanics is the problem of the nature of chemical forces. The forces of homopolar chemical valence could not be explained within the framework of classical physics. Heitler and London, using the example of the hydrogen molecule, were the first to show that these forces of homopolar valence are a manifestation of completely peculiar “wave-mechanical” exchange forces, which have no

analogies in classical physics, but whose existence follows automatically from the peculiarities of the wave equation of matter and the complete identity of electrons. This idea served as the impetus for the creation of an entire new field—quantum chemistry, whose task is to explain the electronic structure of chemical molecules. In this field Soviet physicists are responsible for a number of important works, among which one must mention the works of Rumer and Gelman.

From the electron shell of atoms and molecules we pass to the atomic nucleus, which at the present time is the central problem of physics. We were first introduced to nuclear processes by the phenomena of radioactivity. But what is the nature of these phenomena, what is the mechanism of radioactive decay? Why does uranium have a half-life of \(10^{-18}\) sec., while radium C′, which is only a few places away from uranium in the periodic system, has a period of only \(10^{-5}\) sec.? Until comparatively recently there was no answer to these questions. The theory of radioactive \(\alpha\)-decay was first given by Soviet physicists. The basic idea underlying these works was expressed in general form by L. I. Mandelstam and M. A. Leontovich, who successfully used the formal analogy between the behavior of light waves under total internal reflection at the boundary of two media and the behavior of elementary particles obeying Schrödinger’s wave equation. On the basis of this idea a complete theory of radioactive \(\alpha\)-decay was then given. The circle of concepts used in these works—the idea of the “potential barrier” of the nucleus and of the passage of particles through “forbidden regions”—has firmly entered the language of modern physics, and the theory itself is already expounded in all textbooks and popular books.

A powerful impetus to the experimental study of the atomic nucleus, as is well known, was given by the work of Rutherford and his collaborators on the artificial transformation of atomic nuclei. As soon as Cockcroft and Walton succeeded in carrying out the artificial transformation of lithium by fast protons, these experiments were reproduced in two laboratories of the Union: at the Ukrainian Physico-Technical Institute in Kharkov by A. K. Walter and K. D. Sinelnikov, and at the Leningrad Physico-Technical Institute by I. V. Kurchatov. In the case of lithium the disintegration of the nucleus is accomplished already at relatively low accelerating potentials, but for the destruction of heavier nuclei accelerating fields of hundreds of thousands and even millions of volts are required. Hence there naturally followed the task of creating modern high-voltage laboratory installations. This difficult task has been solved with the greatest success at the Kharkov Physico-Technical Institute, where recently it has proved possible to build an electrostatic generator giving more than 4 million volts, and a pulse generator giving likewise up to 4 million volts.

With the discovery of the neutron, completely new possibilities were found for the artificial transformation of nuclei. The neutron has no charge, and therefore no potential barrier exists for it.

With the aid of neutrons a large number of nuclear reactions were carried out, and Fermi and his co-workers were able in this way to obtain a large number of artificially radioactive isotopes. In studying artificial transformations under the action of neutrons, I. V. Kurchatov obtained a number of interesting and fundamentally important results. Thus, for example, in all cases investigated before Kurchatov’s work the artificially radioactive nucleus obtained underwent a single transformation ending in a stable nucleus. On irradiating ruthenium with neutrons, I. V. Kurchatov succeeded in observing an entire chain of $\beta$-transformations of the radioactive isotope $\mathrm{Ru}^{105}$ that arose, in complete analogy with natural radioactive transformations. Furthermore, in the study of artificially radioactive isotopes of bromine obtained by neutron bombardment, it was discovered that three different radioactive isotopes are produced, whereas one might have expected the occurrence of only two, since bromine has only two stable isotopes: $\mathrm{Br}^{79}$ and $\mathrm{Br}^{81}$. Kurchatov put forward the supposition that nuclear isomers may exist, i.e. nuclei which, with completely identical composition, possess different structure and therefore different degrees of stability. It is very interesting that quite recently Bothe and Gentner also obtained three radioactive isotopes of bromine by the reverse operation—the splitting off of neutrons from the stable bromine isotopes $\mathrm{Br}^{79}$ and $\mathrm{Br}^{81}$ under the action of hard $\gamma$-rays. This shows that Kurchatov’s explanation is correct and that, in this way, he discovered a fact of great fundamental importance.

The remarkable properties of slow neutrons, which possess an especially high probability of penetrating into the nucleus, were investigated in the works of P. I. Lukirsky in Leningrad, and also by Leipunsky in Kharkov. Making use of the rich resources of the low-temperature laboratory of the UPTI, Leipunsky was able to “freeze” neutrons down to very low temperatures (down to $20^\circ,4\,\mathrm{K}$) and under these conditions discovered a number of interesting and fundamentally important phenomena.

For understanding the nature and structure of the atomic nucleus, the study of the energy levels of the nucleus is essential. Information about them can be obtained by studying the spectra of $\gamma$-rays. Just as spectroscopy of visible and ultraviolet rays provided abundant material on which the theory of the structure of the atom’s electron shell is based, one may expect that $\gamma$-ray spectroscopy will provide the key to the study of nuclear structure. An unexpected path to establishing the energy levels of the nucleus was opened when the connection was understood between $\gamma$-rays and the so-called long-range $\alpha$-particles. The latter “slip through,” passing through the potential barrier from high energy levels. Thus, by comparing the energy of normal and long-range $\alpha$-particles, one can directly find the difference of the corresponding energy levels, which turns out to be equal to the energy of the quantum of the emitted $\gamma$-rays.

Another path is connected with the study of γ-ray spectra. However, because of the short wavelength of γ-rays, the usual methods of X-ray spectroscopy prove inapplicable here. One has to resort to studying the velocity spectra of electrons produced by γ-rays, and from these, by an indirect route, to find the spectrum of the γ-rays themselves. D. V. Skobeltsyn successfully used for this purpose the measurement of the energy of Compton electrons produced in the scattering of γ-rays. By placing a Wilson chamber in a uniform magnetic field, he bent the trajectories of the Compton electrons and, from the radii of curvature, could directly determine the energy of these electrons. In Skobeltsyn’s hands this method yielded a large amount of material concerning γ-ray spectra and became widely used. The study of Compton electrons arising in the Wilson chamber as γ-rays passed through it enabled Skobeltsyn to solve an important question about the correctness of the formula for the absorption of γ-rays established by Klein and Nishina with the aid of Dirac’s relativistic wave equation.

Studying Compton electrons in a Wilson chamber placed in a magnetic field, Skobeltsyn was the first to discover “ultra-β-particles” of enormous energy, which proved to be particles of cosmic rays. At the same time he discovered that such particles have a tendency to appear simultaneously in groups. However, the magnetic fields used by Skobeltsyn were insufficient to bend the trajectories of these particles and determine their energy. Using Skobeltsyn’s method, but applying considerably more intense magnetic fields, Anderson in America, Kunze in Germany, and Blackett in England not only confirmed Skobeltsyn’s observations, but also discovered a new elementary particle—the positron. The paired trajectories observed by Skobeltsyn proved to be a special case of the phenomenon of particle “showers,” first discovered on a large scale by Blackett and Occhialini.

The discovery of the positron gave impetus to the detection of a whole series of new and astonishing phenomena. The positron is a particle of an entirely special kind. It has the ability to be “born” simultaneously with an electron under the action of hard γ-rays and, conversely, upon meeting an electron, to “annihilate,” giving rise, in most cases, to two γ-quanta. A number of works by Alikhanov and his collaborators were devoted to the study of these processes of positron production in the field of atomic nuclei and their “annihilation.” A. I. Alikhanov, A. I. Alikhanyan, and L. A. Artsimovich showed that in the process of annihilation two photons are indeed emitted, flying apart in exactly opposite directions. The fundamental significance of this experiment consists in the fact that it demonstrates with complete clarity the applicability of the law of conservation of momentum to elementary acts. The experiment was especially timely, since it was carried out at a moment of sensation caused by Shankland’s experiments (which proved to be incorrect), from which there supposedly followed the inapplicability of the conservation laws to the elementary acts of scattering of photons by electrons. — The ingenious combination of the method

magnetic focusing with the method of two counters operating in coincidence, carried out by A. I. Alikhanov and M. S. Kozodaev, made it possible conveniently to study extremely weak and rare phenomena. In this way Alikhanov and his collaborators studied in detail the aforementioned process of positron production in the field of atomic nuclei. Various aspects of this phenomenon were investigated: its

zing trace—an elastic aftereffect. How is this contradiction to be explained? First of all, solid bodies in which aftereffect, fatigue, and other phenomena are observed are in fact by no means homogeneous crystals. A. F. Ioffe, in one of his early works, showed that in a quartz crystal no true aftereffect is observed. Thus all phenomena occurring beyond the limits of elasticity are the result of the physical inhomogeneity of the solid body.

With a sufficiently large deformation a solid body begins to flow, like a viscous liquid. The mechanism of such plastic deformation was also revealed by A. F. Ioffe, who for the first time applied X-ray analysis for this purpose, observing on a fluorescent screen the Laue pattern during the stretching of rock salt. It turned out that when the tensile force passes a certain limit (the yield point), the spots of the radiograph suddenly split in two, then multiply, and finally are drawn out into whole tails. This shows that the mechanism of plastic deformation consists in the whole crystal breaking up into separate small crystallites, which shift and rotate relative to one another. These works of A. F. Ioffe gave impetus to the development of an entire new field (X-ray analysis of plastic deformation), to which hundreds of works carried out in all countries have been devoted. We have no opportunity here to characterize the numerous subsequent works of A. F. Ioffe’s students and collaborators in this direction. We shall note only two facts. First, I. V. Obreimov, by means of a fine optical method developed by him, showed that slips along definite crystallographic planes begin long before distortions appear in the X-ray picture. Second, A. F. Ioffe discovered, and M. V. Klassen-Neklyudova investigated in detail, an entirely new effect: the discontinuity of the deformation process. Under a continuously applied load, deformation proceeds in jumps, repeating after strikingly equal intervals of time and accompanied by a slight sound reminiscent of the ticking of a clock. This phenomenon was studied by a whole series of Soviet scientists (N. N. Davidenkov, Stepanov), as well as abroad. Its theory was given by N. Davidenkov and M. Klassen-Neklyudova.

A large number of works, also carried out in other laboratories, were devoted to the mechanical properties of solids. Let us note here the numerous works of V. D. Kuznetsov and his collaborators. They developed convenient methods for measuring hardness and other mechanical constants of solids, and studied the influence of various factors on the elastic limit of monocrystals.

their authors. We shall note only a few works that were pioneering in character. To S. T. Konobeevsky and N. E. Uspensky belongs the first detailed work in the literature on the application of X-ray analysis to the study of the internal mechanism of metal-working processes (rolling). N. Ya. Selyakov and G. V. Kurdyumov were the first to show that hardened steel has a crystalline lattice different from the lattice of iron. G. V. Kurdyumov is the author of important works devoted to the mechanism of transformations in alloys. He organized in Dnepropetrovsk a large laboratory and created an entire school of physicists who have been very successfully studying these questions of great importance for metallurgy. One cannot fail also to note the great cultural work carried out in this field. X-ray analysis is at present an indispensable aid to every production process. An X-ray laboratory at a plant, especially a metallurgical one, performs a very important function. Thanks to the development in our country of work in the field of X-ray analysis, factory X-ray laboratories have received cadres of trained workers, and significant work has been done in organizing these laboratories themselves and in propagating their importance in production.

The works of A. F. Ioffe on the study of the strength of solids attracted very great attention in the USSR and abroad. The theory of the crystal lattice, developed by Born, made it possible to calculate what stresses are necessary for the rupture of crystals. These calculated values of the stresses turned out to be many times greater than those actually observed. Thus, rock salt should theoretically withstand stresses up to 200 kg/mm², whereas in reality it ruptures under a load of only 400 g/mm². A. F. Ioffe showed that this discrepancy is explained by the properties of the surface of the crystal. By immersing a crystal of rock salt in warm water, he achieved a strengthening of it by a factor of 10–12. A. F. Ioffe explained this strengthening by the dissolution of the surface layer and the consequent destruction of surface cracks, which greatly lower the limit of strength. These works made a great impression throughout the world and provoked an acute polemic. The fact of strengthening was thereby fully confirmed, but the explanation of it given by A. F. Ioffe was disputed by a number of physicists. A long series of works, both in the USSR and abroad, was devoted to clarifying this question. We cannot dwell on these works, all the more since this question has been repeatedly discussed in the pages of our journal. We shall note only the works of P. A. Rebinder, who independently showed what an enormous role surface conditions play in the strength of a specimen: the introduction onto the surface of an insignificant quantity of surface-active substances lowers the strength many times over.

The electrical properties of solids were likewise subjected to diverse investigation, mainly by A. F. Ioffe and his collaborators. The tangled picture observed when current passes through a dielectric was to a significant degree

clarified by these works. It turned out that in various anomalies the cause was volume charges accumulating in different places. Thus, for example, the decrease in current strength over time, observed in most dielectrics, is explained by the emergence of a counter electromotive force caused by volume charges accumulating near the electrodes. The presence of an insignificant quantity of foreign impurities leads to the accumulation near them of ions that create a volume charge and complicate the picture of current flow.

The study of the electrical properties of dielectrics gave impetus to the investigation of the problem, important for technology, of electric strength. The appearance, discovered by A. F. Ioffe, of fields of enormous intensity (of the order of several million V/cm) in thin layers (of the order of \(10^{-3}\) mm) near the electrodes showed that a dielectric is capable of withstanding fields considerably exceeding the material electric-strength limit known from practice. On the other hand, from theoretical considerations one could expect that a significant decrease in the thickness of the insulating layer should greatly increase its electric strength. Hence the attempts to create “thin-layer insulation,” distinguished by especially favorable properties. These expectations were not justified in practice, but the enormous work carried out in connection with the study of the problem of electric strength, both from the theoretical standpoint (the so-called “thermal theory” of breakdown, developed by N. N. Semenov and V. A. Fock) and from the experimental standpoint (the works of A. F. Walter, B. M. Vul, and others), represents a very significant contribution to science.

From other points of view, and also with great success, the same problem of the electric strength of solids is being studied by the Moscow group of physicists under the direction of F. Kvitner (All-Union Electrotechnical Institute).

Alongside the problem of the conductivity of insulators and metals, in recent years the problem of electronic semiconductors has come to the fore as extremely important in both scientific and technical respects. A semiconductor occupies an intermediate position between a dielectric and a metal. Therefore the study of semiconductors is necessary for clarifying the mechanism of current flow in both classes of solids. From the technical standpoint, the study of semiconductors is important, since they have found wide application as rectifiers and photoelements. A considerable number of works have been devoted to the study of semiconductors, carried out both at the Leningrad Physico-Technical Institute (A. F. Ioffe, D. N. Nasledov, and others) and at the Physical Institute of the All-Union Academy of Sciences (A. G. Goldman). Without dwelling, for lack of space, on their characterization, we shall note the theoretical works of Ya. I. Frenkel, A. F. Ioffe and Ya. I. Frenkel, and the experimental works of D. N. Nasledov, A. G. Goldman and his collaborators, and others.

Quite distinctive phenomena were discovered by I. V. Kurchato-

while studying the electrical properties of Rochelle salt and certain mixed crystals. It turned out that these substances behave in an electric field in a manner entirely analogous to the way ferromagnets behave in a magnetic field. Their dielectric constant has enormous values (in Rochelle salt up to 200,000); the dependence of the dielectric constant on temperature is completely analogous to the dependence of the magnetic permeability of ferromagnets on temperature; they exhibit hysteresis, and so on. This highly remarkable phenomenon, named by Kurchatov ferroelectricity, was subjected to comprehensive investigation, and its theory was given. There can hardly be any doubt that, like ferromagnets, ferroelectrics will find extensive applications in technology.

Finally, in recent years the problem of electrical conductivity in gases has acquired outstanding interest from both the theoretical and the applied points of view. On the one hand, great successes in the study of the structure of matter and the development of the most delicate experimental methods made it possible to pose the question of the elementary processes in a gas discharge; on the other hand, the role of the gas discharge in various electric-vacuum devices (amplifiers, thyratrons, gasotrons, etc.) and the intensive development of questions connected with the construction of new economical light sources drew attention to the study of the macroscopic characteristics of the gas discharge. Among the works of Soviet physicists in this field we shall note the works of N. A. Kaptsov (ignition of the gas discharge, corona), G. V. Spivak (the role of metastable atoms in a gas discharge, the theory of probes, accommodation coefficients), and N. D. Morgulis (cathode sputtering). Among the works connected with the problem of constructing economical gas-discharge lamps, it is necessary to note the works of V. A. Fabrikant (radiation of a discharge in metal vapors), B. N. Klyarfel’d, and A. M. Shemaev.

From the characterization of works devoted to the study of the electrical properties of matter, let us pass to works devoted to the phenomena of magnetism. The remarkable property of electrons, consisting in the fact that a gas of free electrons must possess paramagnetism, was first noted by Ya. G. Dorfman. In his widely known work, W. Pauli (Switzerland) later showed that this property of free electrons is one of the most important proofs of the correctness of the modern quantum theory of metals. But quantum mechanics also leads to another conclusion: L. D. Landau showed that a gas of free electrons in a metal, along with paramagnetic susceptibility, must also possess diamagnetic susceptibility. This conclusion of Landau’s, despite all its paradoxical character, received general recognition.

The most important problem in the theory of magnetism is the question of the nature of ferromagnetism. Quite some time ago, Weiss (Switzerland) showed that the phenomena of ferromagnetism testify to the existence of a special molecular field, but the nature of this field long remained mysterious. Ya. I. Frenkel was the first

discerned here the manifestation of specific quantum-mechanical exchange forces, which play an outstanding role in the most diverse atomic phenomena. Heisenberg’s theory of ferromagnetism, published shortly thereafter and based on the same physical hypothesis, has now received universal recognition.

A major step in the study of ferromagnetism was made thanks to the work of N. S. Akulov and his collaborators. In 1928 Akulov discovered a remarkable regularity that makes it possible to calculate the principal physical properties of ferromagnetic crystals—namely, electrical conductivity, thermoelectromotive force, the change in the shape of a crystal under the action of a magnetic field, and others. This regularity has now received in the physical literature the name “law of anisotropy.” Akulov then gave a complete theory of the magnetization curve of single crystals and polycrystalline bodies. This theory has received universal recognition and is presented not only in specialized monographs but also in general handbooks (for example, in Becker’s book on electron theory and in Møller-Poulsen’s textbook). On the basis of the “law of anisotropy” and with the aid of a special statistical method developed by Akulov and Kondorskii, Akulov finally gave a theory of various galvanomagnetic effects (the Nernst, Hall-Thomson, Righi-Leduc effects, and others).

The extensive field of theoretical and applied optics was developed very intensively by Soviet scientists. The study of optical spectra is one of the most important experimental methods for investigating the structure of atoms and molecules. Empirical data on spectra constitute the ground on which modern atomic physics has grown and strengthened. It was precisely against these data that all its conclusions were tested. In turn, the development of quantum physics had an enormous influence on spectroscopy. From a chaotic mass of empirical material the latter turned into an orderly discipline providing the most important and reliable data on the energy states of atoms and molecules.

Among works on atomic spectroscopy, we should first of all mention those of D. S. Rozhdestvenskii, devoted to the spectra of complex atoms. These works, which appeared during the flourishing of Bohr’s theory, established a whole series of highly important facts. Using the lithium atom as an example, it was shown that although the energy levels of an atom with several electrons differ substantially from the corresponding levels of a one-electron atom, nevertheless it may be asserted that the spectra of these complex atoms also arise from the motion of a single valence electron. In these same works the most important spectroscopic law—the displacement law—was outlined, according to which the “spark” spectra of atoms are analogous to the arc spectra of atoms preceding the given one in the periodic

system; in them the complex spectrum of neon, etc., was for the first time correctly interpreted.

The study of atomic spectra is not the only path to finding energy levels. The method of electron impact, which abroad received brilliant development in the hands of Franck and Hertz, Foote and Mohler, and others, makes it possible by a direct route to establish experimentally the energy states of atoms and molecules. This method, in a somewhat modified form, was applied by V. N. Kondrat’ev, and also by Kondrat’ev and Leipunskii, to the study of critical potentials and elementary processes in the excitation of the molecules \(J_2\) and \(N_2\). For the study of ionization products in those cases when these products are obtained in an unexcited state and, consequently, when there is no possibility of identifying them from spectra, V. Kondrat’ev and N. N. Semenov applied the mass-spectrograph method, simultaneously and independently developed by Dempster and Smyth in America. But an even finer tool is the method of optical excitation of atoms, devised by Wood and first widely used in the exemplary works of A. N. Terenin. Thanks to various improvements introduced by A. N. Terenin into the experimental technique, he succeeded in studying in detail by this route a whole series of atoms—mercury, cadmium, thallium, lead, bismuth, zinc—and in giving the results obtained a perfectly clear theoretical interpretation. A. N. Terenin also studied the so-called stepwise excitation of atoms, i.e., a process in which an already excited mercury atom, absorbing a second quantum, passes to a higher energy level and then radiates. This method makes it possible to check completely the entire scheme of the energy levels of an atom. Terenin himself (together with L. N. Dobretsov) was the first to discover the hyperfine structure of the D-lines of sodium.

Among other spectroscopic works carried out at the State Optical Institute, let us mention the work of S. E. Frish on the hyperfine splitting of spectral lines. As is known, the ordinary fine structure of lines was the first to show with complete clarity that the electron, in addition to the three degrees of freedom inherent in a material point, must be assigned still a fourth degree of freedom, which the Dutch physicists Uhlenbeck and Goudsmit identified with the electron’s intrinsic angular momentum—with its spin. In a completely analogous way, the hyperfine splitting of lines indicates the existence of the spin of the atomic nucleus and provides a method for its quantitative determination. In the works of S. E. Frish, the hyperfine splitting of lines was investigated for a whole series of elements (thallium, calcium, strontium, barium), and results important for the theory of the atomic nucleus were obtained.

If the study of atomic spectra is the basis for investigating the structure of atoms, then the study of molecular, or “band,” spectra plays the same role for molecules. This study also provides an extremely delicate method for deciphering elementary proces-

processes occurring in molecules upon absorption of light. Modern photochemistry has achieved brilliant development precisely thanks to the application of spectroscopic methods. An outstanding role in the de—

the theory of this phenomenon, based on the application of the laws of Brownian rotational motion of molecules. In the works of S. I. Vavilov, the phenomenon of quenching of fluorescence by foreign colorless salts was studied in great detail; the theory of the phenomenon developed by him and his collaborators (I. M. Frank, B. Ya. Sveshnikov) is based on applying to solutions the idea of energy transfer by collisions of the second kind. V. L. Levshin substantiated, with extensive experimental material, the “mirror symmetry” law of fluorescence and absorption curves, previously outlined by Nichols, and gave a quantum interpretation of this law. Recently V. L. Levshin has undertaken an extensive investigation of phosphorescence phenomena, which has already yielded substantial results. Finally, the investigation of the luminescence of liquids under the action of γ-rays, undertaken by P. A. Cherenkov on the initiative of S. I. Vavilov, led to the discovery of a new, quite peculiar type of luminescence. This luminescence was explained by S. I. Vavilov as an effect of secondary fast electrons produced by γ-rays, and the complete theory, developed by I. M. Frank and I. E. Tamm, showed that here we have before us, at first sight, a paradoxical case of optical radiation from an electron moving uniformly in a medium with a velocity greater than the phase velocity of light in the same medium.

The photoelectric effect, along with photochemical phenomena, belongs among the most important actions of light. To investigate the velocities of photoelectrons, P. I. Lukirsky developed an extremely ingenious method of the spherical condenser, which came into general use. With the aid of this method Lukirsky and Prilezhaev made a determination of Planck’s constant that entered all tables as the most accurate; they investigated the velocity distribution of photoelectrons from metals of different thicknesses and established, with great accuracy, the relation between the contact potential difference and the work function of photoelectrons. Questions connected with the construction of photocells maximally sensitive to various parts of the spectrum, down to the far red region, were investigated by P. V. Timofeev and his collaborators. On the basis of this study they constructed excellent photocells.

Very great attention is being attracted by the internal photoelectric effect in dielectrics and by the phenomena of coloration of crystals under the action of light associated with it. Works by P. S. Tartakovsky and his collaborators were devoted to the study of the internal photoelectric effect in crystals. On the basis of these works P. S. Tartakovsky established a scheme of energy levels for certain crystals. Almost simultaneously with the appearance of the well-known works of R. Pohl and independently of him, T. P. Kravets expressed the idea of a kinship between the latent image and the coloration of crystals. The very phenomenon of coloration—

on the same question. Numerous works on the study of the mechanism of the next stage in the formation of a photographic image—development (K. Chibisov, A. I. Rabinovich in Moscow, G. Faerman in Leningrad)—lie beyond the scope of the present article.

From the various manifestations of the action of light on matter we shall pass to another group of problems, also belonging to the interaction between light and matter, but connected with an entirely different circle of phenomena: we have in mind dispersion and scattering.

The study of anomalous dispersion very substantially supplements the information about the atom that can be extracted from purely spectroscopic investigations. Indeed, in order to characterize the motion of electrons in an atom, it is important to know not only the emitted frequencies, but also the intensities of the spectral lines. The latter are determined by the number of emitting atoms in \(1\ \mathrm{cm}^3\) and by the probabilities of transitions between different quantum states. Knowledge of transition probabilities is essential not only for the study of isolated atoms, but also for the investigation of interactions between excited and unexcited atoms, i.e., for questions of energy exchange, so important, for example, in photochemistry. The way to determine transition probabilities is opened by the study of anomalous dispersion. D. S. Rozhdestvenskii carried out works on anomalous dispersion that have become classics. The “hook method” developed by him makes it possible, with extraordinary simplicity, to find the number of dispersion centers. The works of Rozhdestvenskii’s collaborators that followed this work (chiefly those of V. K. Prokofiev and A. N. Filippov) considerably expanded our information about the properties of electrons in atoms and gave an impetus to analogous work abroad. Without dwelling on a presentation of all the results obtained, let us note that, thanks to an improvement in technique—namely, the construction of a fluorite interferometer designed by D. S. Rozhdestvenskii—Prokofiev and Filippov were able to extend the investigation of anomalous dispersion into the ultraviolet region. Thus Prokofiev and Filippov succeeded in observing anomalous dispersion in 25 members of the principal series of sodium and in accurately measuring it for 16 members; the values obtained from this for the transition probabilities proved to be in satisfactory agreement with those calculated with the aid of Schrödinger’s theory. In a number of other works Prokofiev and Filippov studied anomalous dispersion in other alkali and alkaline-earth atoms (lithium, potassium, calcium, strontium, etc.), determined the transition probabilities for “allowed” and intercombination transitions, and verified the applicability of Boltzmann’s law to the increase with temperature in the number of thallium atoms in the metastable state, etc.

In the very latest years the study of this range of questions in connection with the intensities of spectral lines has unexpectedly acquired important practical significance for the construction of economical gas-discharge lamps. Among the works carried out in this field in the Union,

Let us note the works of V. A. Fabrikant and the laboratory he heads at the All-Union Electrotechnical Institute in Moscow. Another path toward investigating the structure of matter with the aid of light is opened by the study of scattering, more precisely, of the molecular scattering of light.

As is known, the very fact of the existence of molecular scattering was for a long time subject to doubt. It is true that Rayleigh, as early as the seventies of the last century, constructed a theory of the blue color of the sky based on the scattering of light by air molecules. However, Rayleigh himself showed that in a homogeneous medium consisting of immobile molecules, light should not be scattered to the sides, since coherent spherical waves issuing from scattering centers, as a result of interference, should in general cancel one another in all directions except the original one. Rayleigh attributed the possibility of the occurrence of molecular scattering in a gas to the presence of disordered motions of the molecules, which hinder the establishment of a constant phase difference between oscillations issuing from different scattering centers. However, L. I. Mandelstam showed that the mere assumption of the disordered motion of molecules is still not sufficient to explain molecular scattering if the number of molecules is sufficiently large. The correct theory of molecular scattering was first created by Smoluchowski and Einstein, who drew attention to the fact that, owing to the occurrence of density fluctuations caused by thermal motion, a medium composed of molecules cannot be regarded as optically homogeneous. As is known, the most favorable conditions for the occurrence of density fluctuations take place near the critical temperature, and this explains the intense “critical opalescence.” Similar conditions are created near the “critical temperature of mixing of two liquids,” which is characterized by the fact that below this temperature the liquids form a two-phase system with a definite interface, while above it they mix in all respects. Near the critical temperature itself, favorable conditions are created for the occurrence of concentration fluctuations, which in this case are produced by capillary waves on the interface. L. I. Mandelstam gave a very elegant theory of this phenomenon and showed that the intensity of surface scattering must be inversely proportional to the capillary constant at the boundary between the two phases.

Since the scattering of light is caused by forced oscillations of electrons under the action of the incident wave, the wavelength of the scattered light, naturally, should coincide with the wavelength of the exciting light. L. I. Mandelstam, however, as early as 1918 theoretically showed that a special kind of scattering is possible, in which the wavelength must change. According to Debye’s theory of heat capacity, thermal motion in a solid may be regarded as an aggregate of elastic waves propagating in the solid in all directions with the velocity of sound. The condensations and rarefactions in such elastic waves form those density fluctua-

properties on which the scattering of light occurs. In fact, the totality of waves of a definite wavelength forms, as it were, a spatial grating that causes the diffraction of light waves. The spatial gratings arising in this way in a solid are not stationary, but move with the velocity of sound. Therefore, owing to the Doppler principle, upon reflection from such moving gratings a monochromatic light wave must split into two waves with different wavelengths. Thus Mandelstam’s theory led to the conclusion that, in observing molecular scattering in solids, the wavelengths in the scattered light must differ from the wavelength of the incident light. For the purpose of experimentally detecting this shift, G. S. Landsberg and L. I. Mandelstam made a thorough study of molecular scattering in crystalline quartz. It turned out that, alongside the unshifted lines of the exciting light, there were also observed lines shifted toward the red and violet sides; however, the magnitude of this shift many times exceeded the shift expected according to Mandelstam’s theory. On the other hand, comparison of the magnitude of the shift with the proper infrared frequencies in quartz showed that the phenomenon can be interpreted from the quantum point of view as if a quantum of the exciting light expended part of its energy on exciting the proper vibrational frequencies in the molecule and was scattered with a correspondingly lower frequency. Almost simultaneously with Landsberg and Mandelstam, this remarkable discovery was made by Raman and Krishnan in India, and since they managed to publish their results before Landsberg and Mandelstam, the name Raman effect became established in the literature for the phenomenon itself. There is no doubt that the discovery of this “combination scattering” belongs among the most outstanding discoveries in physics of the last 20 years; and the fact that, for purely technical reasons, priority remained with Raman does not in the least diminish the merits of the Soviet physicists. This discovery gave impetus to an enormous number of works, numbering in the many hundreds and carried out in absolutely all countries. The method based on it for studying the proper frequencies of molecular vibrations opened enormous possibilities for physics, physical chemistry, and organic and inorganic chemistry. Great credit for the careful study of the physical side of the phenomenon and for the construction of an exact theory of the phenomenon also belongs to Soviet physicists (Mandelstam, Leontovich, Landsberg, Tamm).

That considerably finer splitting of the Rayleigh (unshifted) lines of scattered light, the search for which gave the impetus to the discovery of combination scattering, was also discovered and studied in a number of works by Soviet physicists (Landsberg and Mandelstam, Gross with a number of collaborators). The study of this phenomenon provides important material for investigating the difficult question of the nature of liquids.

Closely connected with the investigations outlined above is a group of works devoted to the diffraction of light by ultrasonic

waves, carried out in the very most recent years. Indeed, if scattering is observed on Debye sound waves, then one should naturally expect that the same phenomenon will be observed with great clarity on artificially excited standing ultrasonic waves in a solid or in a liquid. In fact, this phenomenon was discovered several years ago independently by Lucas and Biquard and by Debye and Sears. In a short interval of time this phenomenon was studied in a number of valuable works by the same group of Soviet physicists (Mandelstam, Leontovich, Rytov, and others).

We shall conclude our survey of works devoted to physical optics with works devoted to the extreme regions of the spectrum. The optical nature of X-rays was established with complete obviousness by the discovery of the interference of X-rays in crystals. However, the classical interference and diffraction experiments are difficult to carry out with X-rays because of their small wavelength. In spite of this difficulty, V. P. Linnik succeeded in carrying out Lloyd’s interference experiment with X-rays and, from the spacing of the interference fringes, in directly determining the wavelength of X-rays.

The region of the spectrum lying on the other side of the visible part, namely the portion of the spectrum between the long infrared and short electromagnetic waves, was discovered thanks to the works of A. A. Glagoleva-Arkadieva and M. A. Levitskaya, carried out quite independently of one another. Thanks to the ingenious method of exciting rays lying in this region, it was possible to detect them with complete clarity and thus to fill the last gap in the unified scale of electromagnetic waves.

Alongside the growth of physical optics in the USSR, one cannot fail to note the remarkable growth of applied optics as well. Optico-mechanical production is one of the most delicate and difficult and, at the same time, one of the most important in economic and defense respects. It is well known that in prerevolutionary Russia this production practically did not exist. The small workshops that did exist had no understanding at all of the essence of the matter, made no calculations, but simply slavishly copied foreign models; optical glass was not manufactured but imported from abroad. And yet—an interesting historical fact!—in the eighteenth century Petersburg was a remarkable center of optotechnical thought: Euler wrote his Dioptrica during his stay in Petersburg. His pupil Fuss published tables for calculating optical systems. Lomonosov and Kulibin built telescopes, and Aepinus built the first achromatic microscope. But all this passed without leaving a trace for the further development of optotechnology in Russia. The works of Euler and Fuss were widely used abroad for many years, while in Russia optotechnology did not exist.

Founded by the revolution, the State Optical Institute, in the twenty years of its existence, has carried out gigantic work in all areas of optical technology. Thanks to the labors of I. V. Grebenshchikov, the USSR now has its own optical glass. The development of methods for polishing glass by the same Grebenshchikov made it possible to manufacture, from our own glass and by our own methods, all manner of objectives, up to enormous astronomical instruments.

The computing bureau, through the work of A. I. Tudorovsky and others, carried out calculations for all types of telescopic, photographic, microscopic, and other optical systems. In the process, original methods of calculation were developed and auxiliary tables were compiled, facilitating the selection of glass types and the course of the calculation. The ingenious and entirely original methods of testing optical systems developed by V. P. Linnik, the methods he devised for centering microscope objectives, which transformed this most difficult operation into a task accessible to any craftsman, the original designs of interferometers by A. A. Lebedev, and work in illumination engineering, photometry, colorimetry, and photography—all this advanced our applied optics far forward and rendered enormous service to our industry.

Among the physical problems on which Soviet physicists have worked with outstanding success, one of the most prominent places is occupied by questions of the theory of oscillations, in particular the theory of nonlinear oscillations. Until recently, physicists and engineers sought in every possible way to reduce all problems in the field of oscillations to linear differential equations. Even in those cases where one had to deal with manifestly nonlinear systems, attempts were made to “linearize” them. This is entirely understandable, since dealing with nonlinear equations is, naturally, far more complicated.

Such an approach was often permissible to a certain degree and led to the clarification of certain aspects of a phenomenon. It is clear, however, that this device has limited applicability, and in certain cases it even leads to grossly erroneous results.

The intensive development of radio engineering since the appearance of cathode tubes has insistently brought to the fore the problem of nonlinear oscillations, since the systems with which one has to deal in modern receivers and transmitters are nonlinear. As has more than once happened in physics in recent years, at the moment when this problem was recognized it became quite obvious that the corresponding mathematical apparatus already existed and had been known to mathematicians for a relatively long time. This apparatus was contained in the works of Poincaré, Birkhoff, and the Russian mathematician A. N. Lyapunov. The application of this apparatus to physical nonlinear systems gave impetus to a large number of very important works that created an entirely new field of physics. The development of this new field is one of the greatest merits of Soviet physicists and, in particular,

of acoustics (N. N. Andreev, S. N. Rzhevkin, S. Ya. Sokolov), in the field of biological physics (P. P. Lazarev), and in a number of other fields; and in the fields touched upon we could not, of course, in any measure exhaust the results obtained or name all the physicists who have worked fruitfully for the development of their science and for the good of the socialist homeland.

At the March session of the Academy of Sciences in 1936, among other things, the question was discussed of what place the USSR occupies in the development within it of scientific work in the field of physics. It is hardly the case, however, that such a formulation of the question is expedient. Our physics is young; it is almost the same age as the Revolution. Its level is difficult to compare with the level of physics in countries where the regular development of science, with continuity ensured, has gone on for hundreds of years. Yet one thing can be stated with complete certainty: at a time when, in the country that in the past gave humanity Kepler, Helmholtz, Gauss, and Kirchhoff, excellent laboratories are now curtailing their activity, from which such scholars as Einstein, Franck, Schrödinger, and hundreds of outstanding young physicists are being expelled or are fleeing; where the “leaders” of physicists turn out to be Lenard and Stark, who have sunk to medieval obscurantism; where bonfires of books are being arranged—at this very time in the USSR scientific work is developing on an unprecedented scale, new powerful institutes are being created, scientific books are printed in unheard-of editions and instantly disappear from the market, and a new generation of proletarian intelligentsia is growing and gaining strength. Our physics is growing not as a self-enclosed “pure” science. It sets itself the task not of development “in general,” but of development for the purpose of assisting in the construction of a classless socialist society. Under the leadership of the Soviet government, under the leadership of the Communist Party and its leader, Comrade Stalin, Soviet physicists are confidently advancing toward new victories on the scientific front for the good of our great homeland and all humanity.

1. For a detailed description of this institute, see the separate article by A. I. Shalnikov, printed in this issue. ↩