Toward the Thirtieth Anniversary of Soviet Physics

Thirty Years of Soviet Optics

T. P. Kravets

1. Optics in Pre-Revolutionary Russia

Interest in optics, both practical and scientific, is already found at the very earliest stages in the development of Russian science. In the Physico-Mathematical Institute of the Academy of Sciences one could still recently see enormous concave mirrors, polished by the hands of Peter’s associate, the well-known Bruce. A member of the St. Petersburg Academy, Leonhard Euler, carried out here one of the first experiments of the wave theory of light, while another of its members—the first truly Russian academician, Lomonosov—engaged in ardent polemics with the “Newtonian theory of the progressive motion of the ether,” that is, with the emission theory of light. At the turn of the eighteenth and nineteenth centuries, the Russian academician Parrot proposed a new variety of the corpuscular theory of light, endowing “luminous matter” with a number of chemical properties.

Closer to our own time, the Moscow professor A. G. Stoletov carried out a series of remarkable studies of “actinoelectric phenomena,” i.e. the photoelectric effect. At the very beginning of the 1890s, the young P. N. Lebedev appeared with an article in which he pointed to light pressure as the cause of the departure from Newton’s law of gravitation for small cosmic bodies. Later, he would glorify his own name and Russian science with two famous works proving the existence of light pressure on solid bodies and on gases. In connection with these works, another of our contemporaries, the Kazan professor Goldhammer, published a remarkable theoretical investigation of the forces of light pressure. The Yuryev professor A. I. Sadovsky predicted various interesting cases of the rotational action of light rays. Later these same questions were taken up from the electronic point of view by K. N. Shaposhnikov. A. A. Eichenwald gave a remarkable physical interpretation of the phenomena occurring in so-called total internal reflection. Theoretical studies on the dispersion of light and on magneto-electric phenomena were published by the same D. A. Goldhammer.

Of the few optical engineers of that time we shall mention V. N. Chikolev, with his classical method for controlling the quality of a searchlight mirror. In the section of light sources it is necessary to recall the most talented invention of the “Yablochkov candle.”

The remarkable experiments of A. A. Belopolsky and B. B. Golitsyn, by which they proved the existence of the Doppler–Fizeau effect, retain their significance to this day. N. P. Kasterin gives a theory of the propagation of light in a medium filled with ball resonators, and also in a medium of layered structure. E. A. Kirillov (Odessa) tests this theory by direct experiment.

One should mention the beginning, belonging to the same period, of the remarkable works on light scattering by L. I. Mandelstam—his famous polemic with Planck, in which he revealed a fundamental error made by the famous physicist; it is also necessary to name his equally remarkable experimental work on the scattering of light at the boundary of two media.

Let us further name the works of P. P. Lazarev on the fading of dyes; the work of T. P. Kravets on the nature of broad absorption bands and his work on the electronic theory of light pressure; several investigations by G. I. Pokrovsky on interference; the works of V. I. Esmarch (Warsaw) on the essence of the phenomena in the reflection of light.

Finally, to this same period belong two classical works of that time: the work of A. I. Ioffe on the elementary photoelectric effect and the work of D. S. Rozhdestvensky on anomalous dispersion in sodium vapor.

This list, not claiming completeness, shows that work in optics stood at a good level in pre-revolutionary Russian physics and was represented by a number of scientists who could create—and indeed later did create—their own school and their own direction. Along with this, the scattered nature of these efforts, the absence of a unifying center, and the insufficient directedness of all the work are striking. This is not surprising: in pre-revolutionary Russia there was no chief prerequisite for such work—a developed optical industry that put its demands before science, together with related branches of production. The country covered almost all its need for optical products by imports. Within the country there were only a few comparatively small branches of foreign firms: Zeiss, Hertz, Krauss, Schneider (Krezo). Besides these semi-artisanal enterprises, one can point only to the optical shop of the Obukhov Plant (later the independent plant “LOMZ”), and to the newly opened workshops of Tauber and Tsvetkov in Moscow, which set themselves, among other things, scientific tasks under the direction of B. S. Shvetsov. Almost on the very eve of the war of 1914–1918, the tsarist government, wishing to stimulate land-surveying work, in connection with

persecuted land policy of Stolypin, with the aid of government subsidies, created a number of small enterprises for the production of geodetic instruments (Tryndin, Gromov, Schwabe, and others).

There were no personnel needed for the optical industry—engineers, foremen, workers. There were no designers of optical systems. The only specialist in this field before the war of 1914 was Prof. A. L. Gershun. He died in 1915. There were no educational institutions for training optics specialists of all qualifications. As an exception, one may mention the Craft School of Tsarevich Nicholas in Petersburg, under the direction of N. B. Zavadsky. Elements of optical production were also taught there. But since there was no demand for optics specialists, only a few chose this specialty. After the war it was transformed first into a technical school, and then into the Institute of Precision Mechanics and Optics.

In the entire country there was not a single optical-glass factory, and this indispensable material was imported by us entirely from Germany, from the firm of Schott in Jena. Only just before the revolution was a decision adopted to create simultaneously two optical-glass factories—in Petrograd and in Izyum.

If the country was not provided with military optics, this was expressed still more sharply for all types of civilian optical instruments: there were no projection lamps of our own, no cameras, no microscopes, no spectral instruments, no polarimetric apparatus. All cinematographic apparatus was also foreign. Examples of this kind could be multiplied without end.

As for photographic materials, there were several handicraft factories of plates, working with imported raw materials.

Lamps for illumination were for the most part imported, and their manufacture in small quantities in our fatherland was likewise carried out with imported raw materials and equipment (vacuum installations, tungsten wire, etc.).

2. OPTICS OF RECENT DECADES

As is known, just before the war of 1914 energetic work began on rebuilding the edifice of theoretical optics—classical electromagnetic optics of the beginning of the twentieth century—on a new foundation. The old optics—the optics of waves and oscillations of a quasi-elastically bound electron and of the electromagnetic ether—after its still recent resounding victories and successes suddenly proved to have exhausted all its possibilities and to be incapable of indicating paths toward the solution of further problems and questions. The theory of relativity knocked the ground out from under the edifice of the luminiferous ether. The theory of quanta, or photons, focused attention on all the failures, on all the weak points of the old theory: on the phenomena of the photoelectric effect, thermal radiation, and, finally, through the work of Niels Bohr, on spectral regularities. In all these fields quantum theory provided

...easy and correct solution, than its inability to cope with such fundamental problems as the explanation of interference, diffraction, and polarization. The brilliant success of the model of the atom proposed by Bohr and developed further in the works of A. Sommerfeld was completed by a new systematics, first of atomic and then also of molecular spectra. A deeper understanding of the mechanism of excitation of individual lines brought with it increased attention to new gas-discharge sources of light. New confirmations of the quantum nature of light appeared—the phenomena of Compton, Raman; photochemistry became quantum, and the theory of luminescence became quantum.

All branches of industry connected in one way or another with optics have undergone radical changes. First of all, automation penetrated into the manufacture of most mass-produced objects and thereby, in many cases, changed the customary appearance of the optical instrument. Objective photometers of various purposes appeared, based on the use of photoelements. Photoelements conquered an enormous field of application in signaling and measuring technology. The importance of optical methods of verification and control grew enormously in many branches of industry.

Lighting technology changed greatly. Gradually, at the beginning of the postwar period, the former vacuum incandescent lamps disappeared, displaced by gas-filled lamps. The latter also caused the old street arc lamp to disappear. It remained only in physics classrooms and in powerful projection installations. And quite recently we have been observing in foreign specialized journals a tremendous “boom” over new luminescent lamps.

The old nonsensitized materials disappeared from photography. The plate is clearly yielding its once leading place to film. Sensitization is penetrating into the near infrared part of the spectrum and, in practice, solves the problem of photographing through the “haze” of the atmosphere at distances of hundreds of kilometers. The sensitivity of layers in practical photography has increased tens of times. New words have been spoken in color photography and color cinema—first in the so-called hydrotype method, and then in three-layer coating. In thirty years silent cinema lived out its age and was replaced by sound films.

On the international market there is an acute hunger for raw material for polarizing apparatus—natural crystals. Undoubtedly connected with this is the invention of new polarizing filters—the so-called polaroids.

The old problem of the measurement and numerical characterization of color is attracting the attention of such luminaries of science as Wilhelm Ostwald and Erwin Schrödinger.

Optics is winning enormous victories in the field of astrophysics. It helps to divide stars into classes, according to their history and devel-

vitally. It establishes the fundamental fact of the dependence between the distance and the radial velocity of remote astronomical objects. It raises to the level of a primary factor the action of the forces of light pressure both outside the stars and, in particular, in the secrets of their internal structure.

The entire development of Soviet optics took place under the influence, above all, of the factors indicated above: the presence of qualified, though at first scattered, personnel capable of directing scientific research in this field; intensive work on the reconstruction of theoretical optics and, alongside this, the industrialization of the country, which became the most important task of the new power from the first day of its arrival; and the creative enthusiasm shown by Soviet scientists in carrying out this great slogan, which in the present case had been assimilated by their best representatives even before the Soviet power, because of military-political circumstances, was able to put it on practical ground.

3. THE PARTICIPATION OF SOVIET SCIENTISTS IN THE RECONSTRUCTION OF THE FOUNDATIONS OF OPTICS

The blockade and intervention of the early 1920s completely closed off communication with the West for Soviet scientists, and those works on the quantum reconstruction of optics, connected chiefly with the name of A. Sommerfeld, which were produced there during that time, remained unknown to us for a long time. But at that same time in our homeland D. S. Rozhdestvenskii took upon himself the same task and carried it out with great breadth and brilliance. A number of his works of that period (“Spectral Analysis and the Structure of Atoms,” “The Significance of Spectral Series,” “Terms of High Order,” “Similarity between the Spectra of One-Electron and Complex Atoms,” “The Series of the Spectrum of Ionized Magnesium from Comparison with the Spectrum of Ionized Helium”) not only give a solution to the same problems that Western European thought set itself, but in particular cases solve them better and more correctly. It is not important that these works of D. S. Rozhdestvenskii remained little known abroad. For us they are a source of pride, since they show that our young science, under the difficult conditions of civil war and isolation from foreign centers, was able to pose and solve the fundamental questions of that time and to gather around them an entire school of young scientists—the future Soviet school of spectroscopists, of which we shall speak later.

After the foundational works on quantum optics of which we have spoken, the largest event was the discovery in 1928 of the phenomenon of so-called combination scattering. The essence of this discovery is deeply connected with quantum conceptions of the nature of light: if a quantum of light is captured by a molecule, part of its energy—a certain smaller quantum—may be expended by the molecule on its slower oscillations; and conversely—the energy of a quantum may

could be amplified at the expense of a vibrational quantum previously acquired by the molecule. In both cases we must have a change in the wavelength of the light emitted back by the molecule. The phenomenon was very difficult to observe at the then existing level of spectrographic technique—both because of the weakness of the new emission lines and because of their proximity to the principal, unchanged line, which was bound to obscure them by its brilliance. It could be discovered only by a great specialist in questions of light scattering, accustomed to all the difficulties encountered here and unable to take the new phenomenon for some secondary stray glows arising in the instrument. Such specialists were found simultaneously at two distant ends of the world. One was Raman in Calcutta, the other—our compatriot L. I. Mandelstam in Moscow, together with G. S. Landsberg. The legal rights to priority belong to Raman, who announced his discovery by cable and not by ordinary postal dispatch, as did our Soviet colleagues. For us it is enough to know that Soviet scientists were simultaneous and independent initiators of a new stage in the development of the quantum theory of light. By their subsequent work along these lines they showed how much creative initiative they had invested in this matter.

Quantum theory leads to the inevitable conclusion that at very weak illuminations, when a very small number of quanta enters the eye per unit time, fluctuations in the magnitude of the observed illumination must be observed. Such a conclusion was drawn by S. I. Vavilov, and such an experiment was carried out by him with a number of his collaborators. Unfortunately, the eye has to be involved—the most sensitive of all existing receivers of light radiation, but one that acquires this exceptional sensitivity only under conditions of long adaptation in complete darkness. Even then, in order to satisfy the condition that a small number of quanta enter the eye, it is necessary to work at the very limit of the eye’s sensitivity (the “extinction method”). The results of the experiments are unambiguous: fluctuations are indeed observed. They are the more appreciable, the smaller the illumination. The magnitude of the deviations of the flashes from a certain mean depends, as is known from statistical considerations, on the absolute number of quanta participating in the experiment; and the latter can be calculated from the magnitude of the fluctuations. Thus we have yet another experimental confirmation of the most fundamental proposition of the theory of quanta-photons and, incidentally, a new method for the absolute measurement of such extremely weak radiations. The experiments were begun and completed before any attempts of the same kind abroad.

It remains for us to speak of one more very fundamental discovery, made likewise in the laboratory of S. I. Vavilov. We are speaking of the so-called “Cherenkov radiation.” This name, after its investigator P. A. Cherenkov, was given to the phenomenon of luminescence observed when $\gamma$-rays pass through various bodies.

γ-rays knock electrons out of the atoms of a substance; in doing so these electrons acquire enormous velocities, approaching the speed of light in a vacuum. Meanwhile, the speed of light in a substance (the “phase” velocity) is considerably less than this speed. We therefore have here approximately the same conditions as when, on the surface of water, say, a steamboat passes with a velocity greater than the velocity of propagation of waves along the water surface. Everyone knows the phenomenon of waves following a steamboat as it moves, spreading backward from it in two rectilinear crests at a certain angle to the direction of its motion. Something similar should be observed here as well, but somehow it is unusual in the age of the theory of relativity to speak of velocities exceeding that of light. Perhaps precisely for this reason the phenomenon was not immediately understood, and some time was required to convince everyone of the correctness of its interpretation. The experiments were repeated in America and fully confirmed the conclusions drawn from his observations by P. A. Cherenkov, and the theory that was created for the phenomenon by S. I. Vavilov, I. E. Tamm, and I. M. Frank. With regard to this phenomenon there is no doubt—it is wholly and completely Soviet in its origin.

We shall confine ourselves to these four facts, regarding their discovery and investigation as the most fundamental contribution of Soviet optics on the path toward rebuilding the very edifice of this science. We shall speak later, in another connection, about other works in various branches of optics.

4. SOVIET OPTICAL INDUSTRY AND OTHER BRANCHES OF PRODUCTION CONNECTED WITH IT

Over thirty years the appearance of the Soviet optical-mechanical industry has changed beyond recognition. The following shifts have taken place: until the 1920s—not a single kilogram of optical glass melted in our country. Now—all the demands of industry for this basic material are fully satisfied by domestic production. The import of optical glass has been closed since 1925. All the needs of our artillery, aviation, and navy for optical instruments of various kinds—binoculars, optical sights, panoramas, stereoscopic telescopes, rangefinders, periscopes, aerial cameras, and aerial photographic lenses—are met by products of our factories. They are made by Soviet engineers and workers, calculated by Soviet scientists, designed by Soviet constructors, and made from Soviet material at Soviet factories.

Our industry has also succeeded in coping with the chief tasks in the field of civilian production. Before the war it saturated the market with motion-picture projection apparatus—first silent, and then sound. Its own instruments were also created for sound recording. The consumer had a certain choice, and for purchas-

tions of cameras: “Fotokor,” “FED,” “Sport,” and some others.

Large factories for motion-picture film were created. The materials they produced were on a par with foreign ones in their sensitivity and resolving power. Their sensitization was also no worse than that of foreign specimens. Instead of small artisanal plants producing food gelatin, which had attempted also to manufacture photographic gelatin, there arose a grand and, in terms of equipment, remarkable specialized photographic-gelatin plant.

The needs of the market were also met with respect to the products of light-source manufacturers: the lamp industry coped well with the fabrication of vacuum lamps and, painlessly and simultaneously with foreign countries, made the transition to gas-filled lamps.

These successes could not have been achieved without substantial scientific-research work. It is necessary to mention the different directions in which this work proceeded.

a) Optical glass

This foremost and most indispensable material for every optical instrument confronts production with a number of serious and interesting tasks. Glass must be transparent, colorless, without foreign inclusions (“stones”), without large gas bubbles and without fine “gnats” of the same origin. It must be uniform in its optical properties throughout its entire mass—without “striae” and coarser inhomogeneities. Its optical properties (refractive index and dispersion) must, within very strict limits, have a predetermined value. The glass must withstand further heat treatment without crystallization and, after such treatment, retain its optical properties unchanged. Its surface must be chemically stable; over time it must not become covered with spots and deposits.

The tasks posed by the production of such a material are, to a considerable extent, purely chemical. These include questions concerning the composition of glasses, equilibria in those complex systems that these glasses constitute, and so forth. But there also arises a series of physical problems. To obtain a uniform mass, the glass must be stirred during its manufacture; therefore the melting regime must be such as to permit such stirring. There is the problem of the dependence of viscosity on temperature, of the width of that temperature interval which is possible without crystallization (“devitrification”) of the glass. Further, it turns out that the very stirring which is necessary in order to impart homogeneity to the mass, in its turn becomes a new cause of the appearance of striae in the glass—through dissolution in the hot glass mass of the material of the pot. A whole series of works by production specialists and laboratory researchers is devoted to these questions of the stirrer. The successes of the latter are connected—

the acceleration of production, an increase in the yield coefficient of usable optical glass, and the transformation of the melting process itself.

A whole series of control methods and instruments had to be created for precise observation of the melting process: an instrument for the rapid determination of the refractive index of glass (“Obreimov’s method”), instruments for viewing specimens for striae, and many others. Next there arose the question of annealing the finished glass in order to eliminate the internal stresses formed during rapid cooling, with which the phenomena of anisotropy are connected. These questions are addressed in the fundamental work of A. A. Lebedev, who, on its basis, arrived at an understanding of the internal transformations undergone, at the annealing temperature, by the quartz contained in the glass. The work of A. A. Lebedev and A. I. Stozharov also gives practical indications regarding the temperature regime necessary for annealing.

The study of the properties of the surface of glass also gives rise to purely physical work, since the study of films on this surface that are invisible to the naked eye is carried out by physical—more precisely, optical—methods based on the application of Drude’s theory, which predicts the optical phenomena (elliptical polarization) that occur in the formation of such films. The work was carried out in the laboratory of I. V. Grebenshchikov. It turns out that such films may also be useful for certain special applications: if, for example, the formation of the film is carried somewhat further, to a greater thickness, then it acquires special adsorption properties, making it akin to silica gel. Moisture over a long time is, as it were, absorbed by such a film, without appearing on the surface as ordinary fogging—an important application for certain special instruments (works of Yu. L. Kurtts, O. S. Molchanova, and others).

Questions concerning the influence of heat treatment of glass on its optical properties, as well as subsequent slow changes in the optical properties of glass, were the subject of thorough and many-year investigations by V. A. Florinskaya, G. O. Bagdykyants, and others.

The X-ray investigation of glass was the subject of works by N. N. Valenkov and E. A. Porai-Koshits in the laboratory of A. A. Lebedev.

Recently practical optics has posed a new question for researchers—the reduction of the coefficient of reflection of light from glass. A solution is possible by applying to the surface of the glass a thin film which, by creating the conditions for interference of the rays reflected at its front and rear surfaces, can considerably weaken the reflected ray, provided the thickness and refractive index of the film substance are properly chosen. In our country the solution was proposed by I. V. Grebenshchikov earlier than abroad. The practical implementation of such “enlightening” of optics is carried out either by chemical deposition or, in vacuum, by evaporation of the film substance.

Then one must also think about strengthening the film that has been formed, which is likewise possible by means of either chemical or physical operations.

Our account is very incomplete and is limited only to the most important cases of the successful intervention of the scientist in the production of that complex and delicate product which optical glass is. It is appropriate to say that the question of producing artificial crystals has also been solved for those cases in which the properties of glass exclude its use (for example, in the ultraviolet region). This problem was posed on a laboratory scale by M. V. Savostyanova, A. S. Toporets, and Kublitskii. At one of the optical-glass factories it has been solved on a production scale (very large crystals of potassium chloride and of certain other substances).

On the question of the coloration of glass, one should first of all mention the work of L. I. Demkina, who established by methods of absorption analysis that the coloration often appearing in Soviet glass is explained by the presence of chromium. Later, work on the coloration of glasses and on colored glasses was carried out in a production aspect by her and by V. V. Vargin, who posed it on a very broad scale. The question of optically colored glass for aerial-survey and other light filters, as well as of signal, decorative, and heat-protective glass (in projection installations, etc.), may be considered solved.

b) Optotechnics

By this term we understand an extensive field of work on the study and measurement of optical systems and instruments, on the control of their optical properties, on methods of their assembly, and so on. This includes the study of focal lengths, the magnitude and location of pupils, resolving power, and also numerous aberrations. The study of finished specimens often precedes the design and calculation of new instruments, in order to form for oneself a visual impression of what, and toward what compromise limit, one should strive in carrying out a particular assignment. On the other hand, every newly manufactured instrument is studied from the point of view of its conformity to the assignment or to the purpose for which it is being built—the work of the calculator, the designer, and the optotechnician thus proceeds side by side, mutually checking and supplementing one another. A series of optotechnical installations is an indispensable accessory of the laboratories of factories manufacturing optical instruments; the optotechnician is the supreme arbiter in questions of the grades of glass used, the quality of manufacture and assembly. He is also the compiler of technical specifications for instruments, instructions for their use, and so forth.

At the beginning of the period being described, the role of optotechnical laboratories was reduced to mastering foreign methods of testing and control. This aspect of the matter must be recognized as very important, since it

corresponds to introducing into the factory that degree of culture without which such fine production as the optical-mechanical industry is impossible. However, genuine creative work begins then, and only then, when we overcome the routine use of others’ instruments and methods and proceed to create our own methods and control instruments. Let us name here only the most important of the innovations carried out in the Union.

In 1928, the optical-mechanical industry was faced with the question of constructing large projector installations. A method was needed for measuring aberration in different zones of the projector mirror. Such a method was created by V. P. Linnik; it represents, in a certain sense, a reversal of the existing Zeiss method. Machines for grinding projector mirrors were built by V. N. Dynkov.

In the same optotechnical laboratory of the State Optical Institute, K. V. Butkov studied a known modification of the Michelson interferometer—the Twyman instrument—for observing optical departures from the ideal form in a given system (for example, a photographic objective). He provided methods for comparing the observed interference pattern with aberrations found by other methods.

V. P. Linnik, having given the Twyman instrument dimensions many times smaller, successfully applied it to the study of microscope objectives.

He also built an instrument for the visual observation of curves characterizing the aberrations of optical systems, instead of the laborious measurement of them point by point on the so-called Hartmann bench.

D. D. Maksutov built instruments for controlling precise surfaces of astronomical objectives of large dimensions. In doing so he transformed the well-known Foucault shadow method into a precise measuring method.

B. M. Koryakin built a universal instrument for testing telescopic systems and for measuring all possible aberrations of such a system.

V. P. Linnik developed a remarkable instrument consisting of two microscopes standing at right angles to one another for studying the microstructure of polished surfaces; before the war it was produced by the Zeiss firm (without special permission from the author).

Among cases of the intervention of optotechnicians in production itself, let us mention once again the work of V. P. Linnik, who created a method for assembling microscope objectives that requires absolutely no participation by a qualified optician. The method proved extremely fruitful during the initial mastery of microscope production by our industry.

Finally, let us mention a whole series of completely new interferometric installations, created by V. P. Linnik for checking polished surfaces, internal channels in large parts of the machine-building industry, gun barrels, and so on.

The foregoing will be sufficient to characterize the level of the work accomplished; it is no wonder that, as a result of this work, as well as of the tremendous creative efforts of our industry, first-class optical equipment was created for our artillery, aviation, engineering, and other defense objects. We are also prepared to manufacture civilian products—from microscopes with achromatic and apochromatic objectives to enormous astronomical objectives; the combined work of the optical-glass factories and the GOI (D. D. Maksutov) also vouch for the latter task; we are able to obtain enormous glass disks and have built powerful units for grinding and polishing them.

c) Computation

As was indicated above, this had to be begun entirely from scratch. The corresponding unit was created under KEPS*) in 1916, and, upon the founding of the State Optical Institute, was transferred to it; A. I. Tudorovskii headed the “computing bureau,” and its earliest collaborators were E. G. Yakhontov and G. G. Slyusarev. Independently of this, the Bureau at GOMZ was engaged in the computation of optical systems in its early years; among its pupils one should name M. M. Rusinov and V. N. Churilovskii.

At the beginning, the activity of the GOI computers was imitative in character and consisted chiefly in copying foreign models. One should not think that even this work did not require certain practical methods and skills, just as any engineering structure, even if it does not claim to create a new type of design, still requires a large number of calculations performed according to schemes worked out in advance. Moreover, an absolutely exact repetition of any optical system is impossible, since, for making a copy, grades of optical glass with constants identical to those of the model are not available, and here certain recalculations are inevitable.

At first, Soviet computers calculated only the simplest telescopic systems—binoculars, stereotubes, and similar special-purpose instruments. Next in order came photographic systems and, finally, microscopic systems. The rapid development of the possibilities of computation is characterized by the following data: in 1918 not a single photographic objective was manufactured within the country; in 1930 the first Soviet camera was issued with an objective of rather average quality (“Ortagöz”). At the present time, all the needs of our Motherland are satisfied with first-class objectives; all of them have been calculated by Soviet computers and, to a certain extent, are original.

*) Commission for the Study of the Natural Productive Forces of the Country.

In particular, mention should be made of M. M. Rusinov’s “Russar”—a wide-angle objective of original design; D. S. Volosov’s series of “Urans”—semianastigmats with meniscus correction of aberrations of this type; “Telemar”—an original telephoto objective; a whole series of “Industars” for defense and civilian instruments, etc. Much work on developing methods for calculating photographic objectives was carried out by G. G. Slyusarev.

An extraordinarily interesting new design for an astronomical instrument was proposed by D. D. Maksutov. This system is catadioptric, mirror-meniscus; the meniscus corrects those aberrations that arise upon reflection by the mirror; the optical power of the meniscus is very small, and therefore it does not introduce noticeable chromatism into the system. A great future may be expected for this system.

Microscope systems were calculated under the direction of E. G. Yakhontov. Here the principal difficulty lay in the exceedingly large value of the “ray” aberrations. In E. G. Yakhontov’s view, in the calculations it was decided to proceed to the consideration of wave aberrations. As was already indicated above, industry had begun to master the production of microscopes.

We should also mention optics for sound-recording and sound-reproduction apparatus. It too was calculated and built in the Soviet Union.

5. LIGHTING ENGINEERING AND PHOTOMETRY

Before the Revolution, strange as it may seem, Russia had no firmly established luminous standards. S. O. Maisel laid the foundation for this at the GOI, whence the work was later transferred to the Main Chamber of Weights and Measures (now VNIIMS). A series of works on the creation of a standard more closely connected with the absolutely black body was carried out by A. A. Dobiashev and others. The works of A. A. Gershun on natural illumination are of great importance; they placed the economic approach to the solution of questions connected with natural illumination on a new footing.

However, the most serious contribution to scientific lighting engineering must be recognized as the theory of the light field given by A. A. Gershun. Unfortunately, it is too complex for elementary exposition. At first it was even met with hostility—among others by such an authority as the late Blondel (who, incidentally, subsequently repented of his criticism, based on a misunderstanding)—but it gradually won recognition. And now the prominent American specialist Parry Moon expresses in his book the opinion that, until very recently, lighting engineering lived by ideas from Bouguer’s time, and that only in our day has a fresh modern current appeared in it, having in mind precisely A. A. Gershun’s theory.

A very interesting study on the illumination of the dark workshops of film factories was carried out by A. A. Gershun, D. N. Lazarev, and K. A. Ventman. The principle taken as its basis was: the maximum effect on

the eye with minimal action on the photographic material. The question is resolved by an exact accounting of the spectral sensitivity of the material and by selecting the appropriate light filters. The color of the illumination is unexpectedly greenish.

A similar principle also forms the basis of a number of works of defense significance on masking illumination, color masking, and deciphering masked objects (M. M. Gurevich, E. K. Pushenko, A. A. Gershun, A. A. Volkenstein, and others).

6. PHOTOGRAPHY AND THE MOTION-PICTURE INDUSTRY

The significance of photography and cinema was appreciated from the first steps of Soviet power, and a whole series of laboratories and institutes were engaged in scientific research in these fields. The principal ones are: the Karpov Institute, where for a long time the photographic program was headed by the late A. I. Rabinovich; NIKFI, where K. V. Chibisov was the long-standing director; the Laboratory of Scientific Photography of the State Optical Institute (T. P. Kravets, and later G. P. Faerman); then TsNIIGAIK, the Kharkov Institute of Applied Chemistry (A. I. Kiprianov), and certain others. Work on individual topics was distributed as follows:

a) Questions of the latent image were studied by M. V. Savostyanova; she regarded the formation of this image as a phenomenon of crystal coloration. This point of view was at the same time advanced by R. Pohl (Göttingen) and T. P. Kravets. But in our country it was possible at once to avoid the error of the German school, which at first considered the latent image to be atomic coloration. M. V. Savostyanova discovered the appearance, under the action of light, of the finest crystals of metallic silver (colloidal silver in the lattice of silver bromide). Under the influence of long-wave radiation the crystals disperse, one may say, before one’s eyes (the Herschel effect). Remarkable works by S. V. Cherdyntsev explained more complex phenomena that are observed when the dispersing light is polarized (the Weigert phenomenon). Yu. N. Gorokhovskii studied the energy relations in the Herschel effect. E. A. Kirillov (Odessa) studied the phenomena of photocurrent under illumination of silver bromide. P. S. Tartakovskii gave a scheme of the energy levels of crystals which explained the observed phenomena. A. S. Toporets sought atomic silver in the coloration of crystals and found it in the case of an admixture of silver halide to a foreign crystal (for example, potassium chloride).

b) On questions of development, two theories were created in the USSR—by A. I. Rabinovich, an “adsorption” theory, and by G. P. Faerman, an electrochemical-thermodynamic one. The latter established (in the works of N. N. Shishkina) the determining significance of the concentration of hydrogen ions for the course of development (the so-called Faerman–Reinders law). K. V. Chibisov, A. I. Kan-Kogan, and A. I. Rabinovich were engaged in the study

microimages of the development process; S. G. Bogdanov—the potential of the developing component of the developing system, etc.

c) A fundamental series of works by K. V. Chibisov was devoted to questions of emulsion synthesis; K. S. Lyalikov and his co-workers studied emulsions from the standpoint of the distribution of grains by size during their ripening; the theoretical part of the work was done by S. V. Cherdyntsev.

d) The stability of emulsions was the subject of investigations by Yu. N. Gorokhovsky and I. R. Protas.

e) Sensitometry was pursued in particular at the GOI, where new standard sensitometric apparatus was prepared for introduction; general sensitometry—by I. A. Cherny; spectral sensitometry—by Yu. N. Gorokhovsky; resolvometry—by F. L. Burmistrov; standard development—by V. A. Veidenbakh. Yu. N. Gorokhovsky carried out a whole series of works on the spectral properties of photographic layers and published an atlas of spectral-sensitivity curves.

f) Photographic gelatin was the subject of investigations by A. V. Bekunov (NIKFI) and G. P. Faerman (GOI); despite the numerous works devoted to both theoretical and production problems, this question in the Soviet Union has not yet been solved to the extent that would be desirable.

7. ORGANIZATION OF SERVICE TO INDUSTRY

In the preceding sections we have had examples of a particularly clearly expressed interaction between scientific research and technical applications. This is a style of work, and Soviet opticians may state with pride how great their contribution is to the cause of serving industry. It is appropriate here to indicate also those organizational forms which this service has taken.

In December 1918 D. S. Rozhdestvensky founded the State Optical Institute. From its first steps the Institute established ties with industry, making in the first years of its existence its chief task the solution of the question of optical glass, and then the calculation of optical systems and the study of optical instruments. At the same time, profound scientific works were being conducted there by D. S. Rozhdestvensky himself, and his pupils were growing up—Frisch, Fok, Terenin, Gross, Chulanovsky. D. S. Rozhdestvensky firmly held the view which he developed at the March session of the Academy of Sciences in 1935: the principal aim of an institute must be to serve some particular branch of industry or several closely related branches; but the industry for which it works must give it the possibility of carrying out work of theoretical significance in that field of science which is contiguous with the corresponding production; production must not be attached to science, but science to production. D. S. Rozhdestvensky’s thought did not seem correct to everyone; he himself readily admitted that between industry, predominating—

T. P. KRAVETS

of legal ideas, and by science, which was in fact called upon to guide this industry, normal relations were not established at once; but he believed that the near future would bring mutual understanding between the sides and a harmonious combination in the institute’s work of the scientific part and the applied part.

It must be noted with satisfaction that optics in the USSR is by no means confined to the framework of the Optical Institute: a significant contribution to it is made by the work of Leningrad University, Moscow University, the Institute of Physics of the Academy of Sciences of the USSR; the aforementioned Scientific-Research Institute of Cinema and Photography, the Leningrad Institute of Precision Mechanics and Optics, the Leningrad Institute of Cinema Engineers, the All-Union Electrotechnical Institute, and many other institutions also take a substantial part in this work, each within the limits of its own special task.

8. WORK ON THE ANOMALOUS DISPERSION OF METAL VAPORS

Let us turn to other cycles of work in optics, not so closely connected with the needs of production, although in certain cases they too provided very important material for the latter. Here we shall put in first place the work of D. S. Rozhdestvensky and his school on the anomalous dispersion of metal vapors. It began with the classic pre-revolutionary work of D. S. Rozhdestvensky himself on the anomalous dispersion of sodium vapor and was the principal basis on which this master of precision optical work trained many of his pupils. At the time when the work was conceived, the author naturally stood on the classical conceptions of the electron—as inert and bound to atoms by quasi-elastic forces. As is known, only these two assumptions about the electron are needed for deriving the Sellmeier formula, and D. S. Rozhdestvensky regarded its verification as a verification of the very foundations of classical electron optics. He created his famous “hook method,” which made possible the rapid measurement of interferograms and the determination of the parameters of the Sellmeier formula. His result was as follows: the Sellmeier formula departs from the experimental data at the very absorption line by no more than 2%. Subsequently, deviations of the same order were also obtained by D. S. Rozhdestvensky’s pupils—V. K. Prokofiev and A. N. Filippov, whose works created for Rozhdestvensky’s laboratory the fame of the best center in the world where these phenomena were investigated. A. N. Filippov, following D. S. Rozhdestvensky’s idea, built the world’s first fluorite interferometer and extended the study of anomalous-dispersion phenomena into the ultraviolet region of the spectrum. Finally, G. S. Kvater managed to show that the deviations mentioned above are hardly of real existence: they are produced by a not entirely correct application of the “hook method,” and, with cautious use of the latter, are reduced to much smaller values.

To his first subject D. S. Rozhdestvenskii returned in the last year of his life. In a work done jointly with N. P. Penkin, he showed with extraordinary virtuosity what possibilities his problem and his method of solving it still contained. He used King’s furnace and extended the study to refractory metals; he compared the results no longer with the classical theory, but with modern conceptions. In particular, the applicability of Boltzmann’s formula to the intensities of individual lines was tested (it was found in a number of cases to be inapplicable); methods were given for determining, by the method of hooks, the intensity of lines when their structure is more complex than a doublet; an appraisal was given of the method of anomalous dispersion as a means of determining line intensities. It is characterized as the most accurate of all existing methods, although not the most sensitive of them. In subsequent applications to problems of quantitative spectral analysis, the method of anomalous dispersion will yet have its say. From the modern point of view, the formulas of anomalous dispersion are derived from other assumptions, and its constants are no longer connected so directly with the number of dispersion centers, with the charge and mass of the electron. The formulas include the statistical weights of known states and transition probabilities; instead of the quantity “damping of oscillations” one must speak of the duration of the electron’s stay in the excited state, etc. Two early works by M. L. Veingerov (A. A. Lebedev’s laboratory) approach the question from this point of view and make use, moreover, of the amount of absorption in vapors and of the magnetic rotation of the plane of polarization produced by them (according to Wood).

9. WORKS ON ATOMIC SPECTROSCOPY

Works on atomic spectroscopy were carried out in great number and with great success, especially in the early years. We have spoken above of the fundamental works of D. S. Rozhdestvenskii in this field. In direct connection with them there arose numerous works by his pupils. Here one should first of all name the works of S. E. Frish, begun in 1926 and continued down to recent days; in them were studied: the spark spectrum of sodium and neon; the magnetic moment of sodium; the hyperfine structure of spectral lines; nuclear moments in connection with the structure of the latter; analysis of complex spectra; the nuclear moments of potassium, mercury, and sodium. The works of his pupils have a similar character, especially the interesting dissertation of V. I. Chernyaev. In the first period of their activity A. N. Terenin and E. F. Gross also dealt with these same questions (the complex structure of the spectral lines of excited mercury vapor), as did A. N. Filippov (together with E. F. Gross—the fine structure in the spark spectrum of cesium) and V. M. Chulanovskii (the influence of an electric field on the serial spectrum of helium); the lively interest in spectroscopic—

...topics also gave rise to a whole series of theoretical works by V. A. Fock. He developed a method (he calls it the generalized Hartree method; abroad it is known as the “Hartree–Fock method”) for “calculating” an atom—for example, the sodium atom—on the basis of empirical data on natural periods and intensity ratios of lines. But with the passage of time an undoubted weakening of work in this field is observed, both in its experimental and in its theoretical part; most of its workers have changed it for other subject matter: E. F. Gross—for problems of light scattering, A. N. Filippov—for anomalous dispersion and for spectral analysis, V. M. Chulanovskii—for molecular spectroscopy. The reason for this phenomenon must apparently be seen in the fact that the topic had, to a certain extent, exhausted itself, at least in principle. In the works of S. E. Frish toward the end of the period a new tendency is observed—the investigation of the conditions of excitation of individual lines as applied to questions of gas-discharge illumination; V. A. Fabrikant is working in the same direction.

A certain new current enters the work on atomic spectroscopy when, on the initiative of D. S. Rozhdestvenskii, the “Commission on Rare Earths” is founded specifically for the investigation of the spectra of the latter, which had been an almost untouched question. In this field A. N. Filippov, A. N. Zaidel, and Ya. I. Larionov had managed, before the war, to achieve certain successes. Unfortunately, three of the four persons named here are no longer alive, and only A. N. Zaidel can continue his work.

10. MOLECULAR SPECTROSCOPY

In molecular spectroscopy one must note first of all the work of V. M. Chulanovskii, who built a remarkable vacuum spectral apparatus for investigating molecular spectra in the far ultraviolet; here both the light source (a condensed spark), and the high-resolving-power spectral instrument, and the photographic technique were carefully developed. All together this made it possible to resolve in a new way several questions concerning the structure of the spectra even of such, it would seem, well-known gases as nitrogen, carbon monoxide, etc. Among subsequent works we shall mention the theoretical investigations of M. A. Elyashevich and B. I. Stepanov on the rotational frequencies of complex molecules, and of M. V. Vol’kenshtein—on the calculation of the intensities of bands of infrared and Raman spectra. Thus the investigations of Soviet scientists cover all regions of molecular spectra—from the far ultraviolet to its infrared parts.

Throughout this entire field much work has also been done to improve the methods of observation and to construct instruments. The apparatus of V. M. Chulanovskii has been mentioned above. Remarkable is the apparatus (S. E. Frish) of a diffraction grating on an enormous, heavy reinforced-concrete...

a farm resting on elastic supports, in a room with constant temperature. Of interest is the attempt by L. B. Ponizovskii to find lines in the near infrared region that, by the simplicity of their structure, would be more suitable for the purpose of comparing the meter with their wavelengths. Unfortunately, the work begun by D. S. Rozhdestvenskii with his collaborators (G. I. Pokrovskii and A. I. Salishchev), which aimed to establish new standards for the rapid determination of the wavelengths of iodine lines instead of Rowland’s iron lines, was not brought to completion. For the infrared region M. L. Veingerov developed a receiver of a new type—opto-acoustic: modulated infrared radiation falls on the gas under investigation in a special chamber; if the radiation is absorbed by the gas, the latter is set into sound vibrations, which are either perceived by ear or converted, with the aid of a microphone, into a measurable galvanometric current. The instrument is successfully used for the purposes of rapid gas analysis and for the control of such installations as recuperative ones, etc. The use of the instrument for purely scientific purposes also appears very promising.

Alongside theoretical work in spectroscopy, work was under way to adapt its results for practical purposes; we have in mind the development of questions and the introduction of spectral analysis. Only in recent years have its methods become the property of factory laboratories and have they been winning, in the latter, a broad field of applications. The work was begun at the Optical Institute by A. N. Filippov and is being continued there by V. K. Prokof’ev. Another important center of work in the same direction was formed first at Moscow State University (the laboratory of G. S. Landsberg), and then at the Physical Institute of the Academy of Sciences (he himself, and also S. L. Mandel’shtam).

11. ABSORPTION OF LIGHT IN SOLIDS AND LIQUIDS

As is known, in solids and liquids the conditions for optical phenomena are considerably more complex than in gases. The absence of a guiding theory often makes it difficult to attempt to understand these phenomena. We can name only individual groups of works in the indicated field. The first belongs to V. V. Butkov. He investigated the absorption spectra of salts in solutions and successfully compared the results obtained with the data available from studies of the atoms of the same salts in other states. The second group of works is connected with the name of I. V. Obreimov. He studied the optical properties of crystals at very low temperatures. The very important and interesting phenomena that he was able to observe in this connection may subsequently acquire practical significance as well; at low temperatures the broad absorption bands of crystals narrow, and the crystal becomes transparent in the spectral region between the individual bands; this circumstance opens up the future possibility of spectral

research in the very far ultraviolet, if only the difficulties of extremely low-temperature techniques are overcome by optical designers*).

M. V. Savostyanova carried out a number of extensive studies of colloidal solutions. Proceeding from Mie’s theory, she was able quantitatively to predict the color and absorption in such systems as colored rock salt, glasses containing copper and gold, silver bromide in which metallic silver has been photochemically separated out, etc. From the same point of view A. T. Atseulov investigated thin metallic layers. The question is acquiring practical importance, since the optical-mechanical industry is beginning more and more to use “thick” and semitransparent layers of metals for its designs.

The last group also embraces questions of absorption in solid and liquid bodies, but exclusively from the point of view of its practical application to light filters. Here we have the extensive work of K. A. Ventman, who established many formulas for filters of the most diverse purpose: for illuminating the dark workshops of film factories (we spoke of this above), for illuminating photographic darkrooms, for isolating individual spectral lines, etc. The questions of the use of light filters are interestingly analyzed in V. A. Faas’s book Light Filters.

Perhaps it is precisely here, in connection with the absorption of light in solid and liquid bodies, that it will be appropriate to speak of one remarkable Soviet invention based on the absorption (or, in another variant, reflection) of bodies in the ultraviolet. As is known, it is precisely in the near ultraviolet region that a vast number of organic bodies, transparent in the visible part of the spectrum, have characteristic absorption bands; the latter are situated in various ranges of wavelengths. Biological preparations photographed by rays from these separate spectral zones will in some photographs give dark images, in others light images of one and the same area of the preparation, depending on the chemical composition of precisely this area. These images can be viewed through different light filters, thereby assigning to each spectral zone of the ultraviolet its own conventional color—for example, to rays of wavelength 2500 Å, violet; of wavelength 3000 Å, green; 4000 Å, red. By methods customary in three-color photography, three such negatives are superimposed on one another; then an image is obtained, brightly colored in conventional colors, and with the aid of these colors areas of different chemical structure in the preparation are excellently separated from one another: chitin, lipoids, cellulose, etc. E. M. Brumberg (GOI) jointly

*) This thought was expressed in a personal conversation by D. S. Rozhdestvenskii.

designed a “three-color” ultraviolet microscope, the introduction of which is tantamount to a new era in observational microscopy as applied to biology, mineralogy and petrography, metallography, etc.

12. SCATTERING OF LIGHT

The scattering of light was studied along several lines and in several centers. On the one hand, this was a continuation of the fundamental work of L. I. Mandelstam and G. S. Landsberg. The work was carried out partly in the laboratory of Moscow State University, and partly at the State Optical Institute. Thus, E. F. Gross and M. F. Romanova discovered the presence of “combination” shifts of the scattered frequency in fused quartz, in glasses containing quartz. V. A. Fabrikant was able to calculate Planck’s constant by measuring the ratio of the intensities of the shifted lines. We have spoken above about the work of M. V. Vol’kenshtein.

On the other hand, questions connected with the “classical” cases of scattering were being vigorously developed. Thus, L. I. Mandelstam, together with G. S. Landsberg and M. A. Leontovich (and also Brillouin in France), predicted a change in the wavelength scattered by a crystal, proceeding from the notion that elastic thermal waves propagate inside the crystal, forming regions of condensation and rarefaction. Reflections of light waves should occur from them, the waves thereby undergoing a Doppler shift. This phenomenon was indeed discovered by E. F. Gross. He, together with Vuks, also investigated the corresponding phenomenon in liquids, to which the Debye concept of thermal waves, strictly speaking, has no direct relation. The phenomenon was discovered in them as well, with certain modifications. The results of the experiments gave rise to a polemic with certain foreign scientists who came to different conclusions. The polemic ended successfully for the Soviet researchers.

Other highly interesting phenomena of light scattering are observed, in accordance with the prediction of theory, in vapors near the bands of their own absorption (L. I. Mandelstam and G. S. Landsberg). The phenomenon is explained “classically” on the basis of the dissymmetry of the curve of anomalous dispersion at absorption bands; on this basis Julius once grounded his theory of the sharp visible edge of the gas envelope of a sphere (the sun).

Finally, the pre-revolutionary work of L. I. Mandelstam on the scattering of light by a fluctuating interface between two liquids (especially near the “critical” point of their mutual solubility) also continued. The phenomenon received a complete theory, which was subjected to experimental verification (works of A. A. Andronov, M. A. Leontovich, and F. S. Baryshanskaya).

In essence, the phenomena of light scattering are characteristic not so much of light itself as of the medium in which they occur, and of the processes that give rise to them. Thus, they prove to be an excellent indicator of such phenomena as elastic-thermal waves propagating within matter, other thermal motions, ultrasonic disturbances, etc. In a whole series of works by Soviet scientists, the method of light scattering was used to study these internal processes, to develop their theory, and for their practical application (L. I. Mandelstam, N. D. Papaleksi, G. S. Landsberg, M. A. Leontovich, P. A. Bazhulin, V. Shimanovskii, Ya. A. Turman, and others).

13. PHOTOEFFECT

When rays of not too great a wavelength fall upon an absorbing body, they may cause considerable displacements of the electrons present in the molecules of the body. These displacements may be very diverse: an electron may be ejected beyond the surface of the body (external photoeffect); it may be torn out of a molecule but remain within the body (photoionization, internal photoeffect); it may pass, while remaining inside the molecule, to a higher energy level (“excitation”). In this process, various secondary phenomena may occur: the electron ejected from the molecule may help to bring about the bonding of the remaining positive ion with a new negative one (a photochemical reaction); in passing back to its former energy level, it may initiate various phenomena of luminescence. We shall consider the latter separately.

Among the studies devoted to the external photoeffect, it is just to single out the work of P. I. Lukirskii and S. S. Prilezhaev. It was undertaken to solve a fundamental problem—the rigorous verification of Einstein’s formula—and it achieved its goal with remarkable success. The authors eliminated many errors connected with the influence of the edges of the capacitor by conducting the observations in a spherical capacitor; the work is in general classical in the elegance of its method and experiment. The authors unquestionably establish the validity of Einstein’s law and, on the basis of their experiments, determine the value of Planck’s constant with an accuracy considerably exceeding the only measurements of Millikan made up to that time.

Among the works on the internal effect, the earliest is that of N. K. Shchodoro, carried out during the period of the revolution (in the laboratory of P. P. Lazarev). It may be considered an established fact of photoionization of dyes in solution. At that time, no other possibilities under the action of light on a dye (for example, its excitation) were imagined. Later, the internal photoeffect more than once served Soviet researchers as a method for establishing energy...

levels in crystals. From this point of view A. F. and A. V. Ioffe worked; they established complete correspondence between the absorbed light energy and the photocurrent in the crystal—a fact quite natural, but one that gave rise to various misunderstandings because of an incorrect accounting of the absorbed energy. Similar apparent deviations in thick layers of an absorbing crystal are observed because it is incorrect to regard the absorption of energy as uniform throughout its entire thickness—this was explained by the same authors. Finally, P. S. Tartakovsky and his coworkers dealt with questions, not fully clarified, concerning the occurrence of photoconductivity in the formation and in the destruction of atomic coloration. To elucidate the picture of the formation of the latent image, E. A. Kirillov and his students studied the phenomena of photoconductivity in silver halide.

As is known, the photoelectric effect has served as the basis for numerous practical applications, in the form of photoelements of various types, electron-optical converters (Holst tube), etc. Receivers of this kind serve for the construction of objective photometric instruments—luxmeters, densitometers, and so on. In particular, for example, a selenium photoelement has a spectral distribution of sensitivity rather close to that possessed by the human eye. With a light filter one can without difficulty eliminate all the difference still observed between them. This problem was solved at the GOI, in the laboratory of M. M. Gurevich, by E. K. Putseiko. There too S. I. Freivert developed the technological process for manufacturing such photoelements.

Very extensive work on the construction of photoelements with secondary emission was carried out at the All-Union Electrotechnical Institute by P. V. Timofeev. The “L. A. Kubetsky tube” is also well known. Instruments of this type, as energy receivers, give in the ultraviolet a sensitivity approximately an order of magnitude higher than all others.

Unsuccessful attempts were made to penetrate with the photoelement also into the infrared region.

Just before the war the Physical Institute of the Ukrainian Academy of Sciences produced for this purpose a very perfect sulfur-silver photoelement.

14. PHOTOCHEMISTRY

In close kinship with the photoelectric effect stand, as we know, the phenomena of photochemistry. Before the revolution P. P. Lazarev began to study them, using exact physical methodology. He transmitted his experience in this matter to his school in the persons of T. K. Molodoi and E. V. Shpolsky.

The latter at first investigated the photochemical action of enormous quanta of X-rays. Subsequently, in the works of E. V. Shpol—

—sky and his collaborators studied the phenomenon of photochemical sensitization and established essential features of this phenomenon when it takes place not in the gas phase but in solutions. A. I. Rabinovich and Bokinnik studied, under similar conditions, the phenomena of sensitization—a question of extraordinary importance for photography, but one that has not yet been satisfactorily resolved.

From another point of view, namely from the standpoint of the state in solution of the sensitizing dye, E. A. Nikiforov (Laboratory of Scientific Photography at the State Optical Institute) approached the question before the war itself.

The conditions under which photochemical reactions proceed in a gaseous medium are, of course, simpler and more transparent, and the greatest successes in the early stages of their study were achieved precisely here. In our country the works of A. N. Terenin, V. N. Kondrat’ev, and partly K. V. Butkov are connected with them. We shall not follow the chemical side of the matter; for us the physical methodology of studying the question is of particular interest.

In gases the bands and their “edges” are established easily and with enormous—“spectroscopic”—accuracy, and from this the magnitude of the quantum absorbed by the molecule is calculated, and then the energy entering one mole of the illuminated substance. If, further, luminescence is observed during the formation of a new phase, then from its position in the spectrum the energy going into this emission is again determined with enormous precision. As a result, excellent quantitative information is obtained about the energy consumed, the residual energy, and the energy that has gone properly into the reaction. Einstein’s quantum law, “one quantum for one reacting molecule,” serves here as a constant basis for reasoning and quantitative accounting.

The very nature of the processes, the intermediate products, and the kinetics—all are established by the corresponding spectroscopic arguments.

A. N. Terenin’s works began in 1926 with the study of the reactions of photodissociation of halogen salts of metals—sodium iodide, silver iodide, and others—in the vapor state. They were continued both by him himself and by him in collaboration with K. V. Butkov, and separately by K. V. Butkov and by a whole series of pupils and collaborators of A. N. Terenin: I. M. Frank, G. G. Neuymin, N. A. Prilezhaeva, B. Popov, L. N. Kurbatov, K. S. Lyapikov. The objects of investigation gradually became more complex, the problem broadened; besides purely photochemical aims, the investigation was assigned the task of penetrating deeply into questions of the chemical structure of the most complex molecules, such as, for example, organic dyes. Another center of similar work was created by V. N. Kondrat’ev.

At the dawn of photochemistry the Russian investigator Grotthuss intuitively formulated its basic law. In our time we can, with complete

rightfully claim one of the first places in scientific photochemistry, where Soviet scientists have created an independent, new, and progressive direction and have advanced far ahead the investigation of this important field.

15. PHOTOLUMINESCENCE

The field of photoluminescence phenomena is closest to those discussed above, but its investigation began considerably earlier. We already know from textbooks the “Stokes rule” that belongs here: the wavelength of photoluminescence is always greater than the wavelength of the light exciting it—always, except in those cases when the photoluminescence is “anti-Stokes.” Einstein’s law also gives an explanation of this: one quantum of exciting radiation gives rise to one quantum of photoluminescence; only relatively rarely is the capture, in this process, of an additional quantum at the expense of thermal motion in the luminophore or of other sources of energy probable.

For gases, Wood’s classical works prepared the application of Bohr and post-Bohr ideas about energy levels in atoms and molecules, with calculation of the probabilities of transitions between them by means of the Boltzmann formula, and so on. But most of the old, long-known phenomena of fluorescence and phosphorescence take place in liquid and solid media. Here a rational reconstruction of the entire edifice had to be carried out from the very beginning; this task was undertaken by S. I. Vavilov, and later by his school (the luminescence laboratories of the State Optical Institute and of FIAN).

First of all, what is investigated here is the magnitude of the yield coefficient of the secondary reaction—a task not always easy because of the difficulty of measuring the exciting short-wavelength energy. Here an unexpectedly simple regularity proves to hold—the “Vavilov law”: the yield coefficient (if it is counted in quanta per quantum) is the same throughout the entire spectrum. This regularity leads to two conclusions. On the one hand, it forms the basis of a method for measuring ultraviolet radiation by the brightness of the visible glow excited by it; on the other hand, it points to deep causes of a general character, which nevertheless limit the useful yield of secondary luminescence in the same way in all regions of the exciting spectrum. For the final clarification of the question, knowledge of the absolute value of the photoluminescence yield was required. It proved, generally speaking, to be very high and in some cases differed from unity by only a few dozen percent. This is a fact of enormous practical significance, underlying the construction of luminescent lighting; its role here may be likened to the role of the laws of blackbody radiation in the construction of incandescent lighting.

If the yield is not equal to unity, then some causes limit its magnitude; the school of S. I. Vavilov sees these causes in “collisions of the second kind” between the particles of the luminophore and the particles of the liquid. From this point of view it is understandable that this “quenching” does not depend on the position in the spectrum of the exciting radiation. Of great interest is the more complex case of “concentration” quenching at high concentrations of the luminophore itself, owing to special regularities then observed.

Finally, especially interesting are the phenomena of polarization of fluorescence and the dependences of it on wavelength discovered here. The collaborators of S. I. Vavilov (A. A. Shishlovskii, B. Ya. Sveshnikov, A. N. Sevchenko, Z. L. Sverdlov, I. A. Khvostikov, P. P. Feofilov at the State Optical Institute; V. L. Levshin; L. A. Tumerman at the Lebedev Physical Institute, and others) systematically investigated the luminescence spectrum, its yield, quenching, and polarization. All the data taken together made it possible to create the coherent picture of the phenomena which we could only outline here.

In conclusion, let us mention the great defense applications of our knowledge of photoluminescence, as well as the numerous practical procedures that resulted from its study.

16. THE EYE AND VISION

Soviet researchers also worked on another branch of optics—ocular and spectacle optics. Correction of vision is a factor of enormous economic significance, since by it the working capacity of such a vast circle of persons is increased, and to such a degree for each, that the total effect achieved cannot be subjected even to approximate calculation. It should be noted that much propaganda work in this direction was carried out by L. N. Gassovskii (Laboratory of Physiological Optics, State Optical Institute).

The eye was studied in the Union not only from the point of view of its correction, but also in many other respects. One of the pioneers of this study was P. P. Lazarev, in whose school, from the point of view of the ionic theory of nervous excitation developed by him, various questions were studied concerning the sensitivity of the eye, its adaptation, and so forth. Subsequently, various directions in the study of the eye took shape: stereoscopic vision, eye fatigue, color sensitivity, anomaloscopy, and so forth; the dependence of visual acuity on the angular dimensions of the object, its brightness, and its contrast. These works were concentrated in several centers: in the laboratory of N. T. Fedorov and S. V. Kravkov; at the State Optical Institute—in the photometric laboratory (G. N. Rautian), in the colorimetric laboratory (L. I. Demkina), in the laboratory of physiological optics (L. N. Gassovskii, V. G. Samsonova, N. I. Pinegin). To N. I. Pinegin belongs an excellent work on the sensitivity of the eye in regions of the spectrum bordering on the visible.

17. ATMOSPHERIC OPTICS AND ACTINOMETRY

It remains for us to touch upon work in atmospheric optics and actinometry. Actinometry in particular was “fortunate” already in prerevolutionary Russia: important work on determining solar radiation belongs to O. D. Khvolson; the practical actinometer, adopted on an international scale, was constructed by V. A. Mikhelson. Extensive work on recording direct and diffuse radiation and other phenomena was carried out at the Pavlovsk Observatory by S. I. Savinov. Later, up to the present time, it has been conducted on an even broader scale by N. N. Kalitin.

In recent years, in connection with the needs of various agencies, and especially of the navy and aviation, the question of “visibility” has aroused increased interest. Attempts to define this concept more precisely and to establish methods for its practical measurement are very numerous. Previously, the so-called “visibility filter” of Wigand was used for this purpose; in our country it was constructed by K. A. Ventma. At present there are a number of instruments proposed for this purpose by V. A. Faas, N. E. Rytin, and others. Among them we shall mention the “smokemeter” of V. V. Sharonov.

The solution of the problems put forward in this area by practice encounters the far from sufficient theoretical study of the phenomena of atmospheric turbidity.

Of outstanding significance are the works of E. S. Kuznetsov and V. A. Ambarzumian, in which, for the first time, the problem of the propagation of light in a turbid medium was formulated with sufficient rigor and solved for a number of special cases, and the theory of non-horizontal visibility was also developed.

Among earlier works one should mention a series of articles by G. I. Pokrovsky and I. I. Tikhanovsky, who, among other things, was interested in questions of polarization and the case of anisotropic molecules. V. G. Fesenkov and I. A. Khvostikov dealt with questions of light scattering in the upper layers of the atmosphere (under twilight conditions) and with the development of optical methods for studying their structure.

A number of works by Soviet scientists are devoted to the question of the role of secondary scattering and of the real scattering indicatrix (V. G. Fesenkov). Analogous questions of the optics of the sea were successfully developed by V. V. Shuleikin.

Very interesting results were obtained by S. F. Rodionov, who studied ultraviolet, the most strongly scattered radiation, as well as the problem of atmospheric ozone.

V. G. Fesenkov and I. A. Khvostikov carried out a number of studies on the glow of the night sky, which contributed much of importance to the understanding of this complex and difficult-to-study phenomenon.

At present, such work is concentrated in the Geophysical Institute of the Academy of Sciences of the USSR (the laboratory of I. A. Khvostikov) and the In—

Institute of Astronomy and Physics of the Academy of Sciences of the Kazakh SSR (V. G. Fesenkov).

Let us also point to a number of practical questions and applications in the field of solar radiation. B. P. Weinberg and V. B. Weinberg developed heliotechnical designs; A. M. Titov wrote on the best methods of capturing energy in this connection; D. A. Fedorov (Agrophysical Institute) pointed out well-known organic films which, if used to replace the glass of greenhouses, considerably increase the effectiveness of the latter.

18. OPTICAL LITERATURE

In the last section of our survey we shall say a few words about the literature on optics.

In pre-revolutionary times we had (in the 1890s) A. G. Stoletov’s Introduction to Acoustics and Optics, remarkable for its day. Now, of course, it is hopelessly obsolete. A significant contribution to the pedagogical literature was made by the optical volume of O. D. Khvolson’s course, but after the author’s death the course was neither revised nor reissued.

Everything that went beyond the limits of these books had to be drawn from foreign sources. The market showed no demand, and therefore even some Russian physicists published their works abroad. Such, for example, was Goldhammer’s brief but very interesting little volume Dispersion.

The situation changed sharply after the revolution.

During these years such fundamental books appeared in Russian translation as Drude’s Optics, Wood’s Physical Optics, the optical volume of K. Scheffer’s Theoretical Physics, and courses in optics by M. Born and Schuster. Among original Russian courses there are the newer books by D. A. Rozhansky, the newly revised optical volume of V. A. Mikhelson’s Physics, and the completely modern university course by G. S. Landsberg. Finally, there is also the theoretical course—V. K. Frederiks’s Electromagnetic Theory of Light.

There are two fundamental courses on the theory of optical instruments (A. I. Tudorovsky) and their calculation (G. G. Slyusarev). On spectroscopy there is A. N. Terenin’s course; on its technique, S. E. Frish; on spectral analysis, A. N. Filippov and S. L. Mandelstam. On photography, extensive courses by K. V. Chibisov and Ya. M. Katushev and by V. I. Sheberstov have appeared, as well as a translation of Angerer. On photometry and pyrometry there are translated books by Fabry and Ribaud. In addition, a number of domestic and translated monographs on various special questions have been published.

Let us permit ourselves to confine the discussion to these principal indications.

It seems to us that our far from complete survey has given some idea of the affairs of Soviet optics. We wish it the opportunity to have its own say as well. We have in mind the long-overdue need for a special journal for optics.

We would like our Soviet journal, among the various foreign optical journals, to say this word of its own in a new way; it seems to us that the unification, in a single organ, of questions of science and technology, of laboratory and production experience, of theory, calculation, and the machine tool would be such a new word, sounding in the Soviet manner.