Nikolai Dmitrievich
Papaleksi

NIKOLAI DMITRIEVICH PAPALEKSI

S. M. Rytov

On the night of February 3, 1947, Academician Nikolai Dmitrievich Papaleksi suddenly passed away. Not only Soviet science, but world science as well, lost one of its most outstanding representatives, a scholar of great stature, one of the pioneers of radio and founders of domestic radiophysics and radio engineering, a man who was selflessly devoted to science, imbued with a sense of responsibility to his country and an awareness of duty, who was an example of persistence, diligence, and principled integrity. Those who knew N. D. more closely, who knew what exceptional responsiveness and what kindness were concealed beneath his usual external reserve, experienced, in connection with his death, a great personal grief as well.

N. D. Papaleksi was born on December 2 (old style), 1880, in Simferopol. His father, commander of a battalion of the 51st Lithuanian Regiment, died when N. D. was four years old. N. D. studied first at the Simferopol gymnasium and then at the Poltava gymnasium, and already in those years showed an interest in the exact natural sciences. While still a gymnasium student, he ordered books on physics, mathematics, and astronomy for himself, obtained textbooks even from abroad, joined the Poltava circle of lovers of the physical and mathematical sciences, and for a long time (until 1907) remained an active member of it. His first scientific work, “On the Harmonic Properties of a Complete Quadrilateral and Some of Its Applications,” published after he had already gone abroad, N. D. printed in the report of the Poltava circle.

In 1899, after graduating from the gymnasium with a gold medal, N. D. went abroad to continue his education. For one year he studied at the University of Berlin and then transferred to the University of Strasbourg, where the physical and mathematical sciences were at that time represented by a whole group of outstanding people. The chair of experimental physics and the Physical Institute of the university were headed by the widely known scholar, Prof. Ferdinand Braun, whose scientific and personal influence played such a great role in the life of Nikolai Dmitrievich,

and L. I. Mandelstam. It was there, at the University of Strasbourg, that N. D. became acquainted with L. I. Mandelstam.

Their acquaintance came about by chance: L. I. saw that N. D. was reading a Russian newspaper, and thanks to this it became clear that they were compatriots. They did not, however, become close immediately.

They attended only a few lecture courses together. Their interests sometimes did not coincide at all. N. D., for example, loved astronomy and was one of the two, or even the only, listeners to the Strasbourg astronomer. He was also interested in meteorology, about which L. I. usually merely joked. Gradually, owing in large measure to L. I.’s immense charm and open character, the reserve characteristic of N. D. in those years was overcome, and between them there arose a closeness and a scientific fellowship that bound them thereafter for their whole lives.

The beginning of the scientific activity of both N. D. and L. I. Mandelstam was determined by the questions that most occupied Prof. Braun at that time—questions of electrical oscillations and their applications in radiotelegraphy. N. D.’s dissertation for the degree of doctor of physics (phil. nat.) of the University of Strasbourg, which he submitted in 1904 after passing all examinations with the highest distinction (summa cum laude), was devoted to the theory and experimental investigation of a dynamometer intended for high-frequency currents. The dynamometric principle later formed the basis of a whole series of measuring instruments of Papalexi and Mandelstam.

During the following ten years N. D.’s scientific activity took place at the University of Strasbourg and its Physical Institute—until 1911 as a laboratory assistant of the institute and assistant to Prof. Braun, and then as a Privatdozent in the department of physics. From N. D.’s own recollections of L. I. Mandelstam we know in what an exceptionally favorable and scientifically rich atmosphere these years of growth and perfection passed.*)

Very soon, while N. D. was still a student, his scientific work with L. I. Mandelstam began. Their first joint article, however, appeared only in 1906. It was an investigation of a method for obtaining oscillations having a prescribed phase shift. The aim of this method was the creation of directed radio radiation; the difficulties, however, with which the development of the method was connected arose from the fact that the matter concerned damped oscillations excited by a spark.

During the whole of his stay in Strasbourg, N. D. was occupied above all with electrical oscillations. Of course, one can point to a number of his investigations belonging also to other fields of physics. In 1907 he spent time in Cambridge, where in the laboratory of J. J. Thomson

) See N. D. Papalexi, “A brief sketch of the life and scientific activity of Leonid Isaakovich Mandelstam,” Advances in the Physical Sciences, 27, 143 (1945), and “From scientific recollections of Leonid Isaakovich Mandelstam,” Izv. AN SSSR (physical series), 10*, No. 2, 127 (1946).

studied the excitation time of fluorescence. In Strasbourg, together with Mandelstam, he conducted experiments on electron inertia in a metal, preceding by four years the well-known experiments of Tolman and Stewart. Mention should also be made of his work on gas discharge (a high-pressure mercury arc) and on comparing the brightness of an electric spark and of the solar disk. The principal studies, however, were in the field of electrical oscillations and radiotelegraphy: studies on methods of measuring high-frequency currents and the parameters of oscillatory circuits, on directional radiation, on direction finding by means of a frame antenna, on the theory of the rectifier, and others.

N. D. devoted much effort and time, moreover, to that part of the work which, in the opinion of many, is the least attractive. Physical ideas from the field of radio measurements, arising as a result of collective research at the Strasbourg institute, were brought by N. D. to full completion, to technical designs. For this purpose he traveled to Berlin, where the firm Telefunken, whose consultant Braun was (and later also L. I. Mandelstam), provided the appropriate opportunities and means. These trips became especially frequent in the second half of the Strasbourg period. Into the work that we now call “implementation,” N. D. was naturally drawn by the interests of the common cause. Yet in the fact that it was precisely he who assumed the greatest share of the burdens connected with technical development and with patent matters, other circumstances—or, more precisely, features of N. D. himself—played an essential role.

He was organically incapable of leaving work unfinished; he felt obliged to bring it to completion. The feeling of completion arose in N. D. only when the fruit of theory and experiment was not merely the clarification of a question, but also a practical application, a corresponding method or instrument, a direct entry into technology. This trait of N. D.’s scientific cast of mind can easily be traced later throughout his whole life, and, undoubtedly, it was thanks precisely to this trait that N. D.’s scientific collaboration with L. I. Mandelstam subsequently led to such outstanding practical results in the field of radio.

However, in those early years, of which we are now speaking and which to a considerable extent were still years of apprenticeship, it is hardly possible to seek in this striving for technical completion an exhaustive explanation. After all, “implementation” and patent affairs undoubtedly harmed N. D.’s scientific pursuits, tore him away from scientific research work, and often in themselves afforded him not very much satisfaction. Year after year, the numerous letters of Nikolai Dmitrievich speak of this.

Thus, to the question of why N. D. took upon himself all these burdens, one cannot answer solely by referring to his inclination, to his persistence, or to his sense of duty, although this feeling held him in an iron grip throughout his life. Undoubtedly, here played ...

a great role as well. N. D. saw that this practical aspect of the matter was entirely unbearable for L. I. Mandelstam; he saw that Mandelstam literally became ill from the Berlin excursions into engineering, that, despite all his respect for practical application, Mandelstam, in essence, lost interest in a question as soon as complete physical clarity had been attained in it, that doubts overcame him concerning the success of “implementation” (as a result of which Mandelstam, in N. D.’s own words, usually acted as “the devil’s advocate”). And so, deeply and truly loving L. I., N. D. spared him and with all his strength—both in those years and up to the last day of L. I.’s life—tried to relieve him of tasks that weighed upon him. He always reassured Mandelstam, assuring him that “we shall do all this,” and L. I. indeed calmed down, knowing that the matter was in reliable hands. This touching solicitude, this deep attachment, which did not stop short of sacrificing his own scientific interests, is the second trait of N. D. that must be remembered when speaking, in particular, of his activity in Strasbourg—a trait that ennobles his image still further.

In 1911 N. D. submitted a dissertation for the right to lecture (venia legendi) and took the position of Privatdozent at the University of Strasbourg. N. D.’s dissertation deserves somewhat more detailed attention. In it he analyzed phenomena occurring in an alternating-current circuit containing self-induction and a nonlinear element—a rectifier or electric valve whose conductivity is different for the forward and reverse directions of current. N. D. obtained a number of significant results concerning the operation of such a rectifying device, but the main point does not lie in this. First, N. D.’s dissertation was one of the earliest studies of nonlinear oscillations. Second, in it the so-called method of fitting was applied for the first time to nonlinear oscillations. This method consists in replacing the actual nonlinear characteristic of a device by a broken line made up of straight-line segments, which leads to replacing a nonlinear differential equation by a system of linear equations whose solutions are joined (fitted) at the transition points from one segment of the characteristic to another. In recent times this method, to which Mandelstam and Papaleksi always attached great importance, has received further brilliant development in the works of A. A. Andronov on the theory of automatic control.

To 1911 also belongs N. D.’s trip to Petersburg, where he took part in the work of the Second Mendeleev Congress on General and Applied Chemistry and Physics. At a meeting of the radiotelegraphy subsection (December 23) N. D. was elected honorary chairman of the session and then delivered a report, as stated in the minutes, “on new methods of measurement in the field of high-frequency currents, developed by the speaker jointly with L. I. Mandelstam at the Strasbourg Physical ...”

NIKOLAI DMITRIEVICH PAPALEKSI

institute. The speaker set forth the theory and design of various instruments he had developed for measuring wavelength, damping decrements, and current intensities. At the conclusion of the report, the dynamometric decrement meter and ammeter described by him were demonstrated in operation.

The year 1914 found N. D. in the midst of his work. After successful experiments on radio reception from Paris in Strasbourg using Braun’s loop antenna, and experiments on direction finding and on comparing the field strength of radio waves, N. D. and L. I. Mandelstam were preparing once again to take up the study of electron inertia. But the First World War was approaching; an ultimatum was presented to Serbia, and in July N. D. and L. I. returned to their homeland. They traveled together through Halle, but crossed the border at different points: L. I. went to Odessa, while N. D., after visiting his mother in Poltava, set off for Petrograd. From that time on, all of N. D.’s activity was inseparably connected with the development of Russian radiophysics and radio engineering, in which he immediately occupied an outstanding place. N. D. was invited as a consultant on physical questions and as head of the experimental laboratory of the plant of the Russian Society of Wireless Telegraphs and Telephones (ROBTiT) in Petrograd, and devoted himself entirely to solving those most important practical tasks that the war set before the radio industry.

One of these tasks was the immediate provision of direct radio communication with France and England. This required a fundamental modernization of the experimental 100-kilowatt spark station located at the plant, and such an improvement of the receiving apparatus as would make it possible to receive not only by ear but also to record on a phonograph or tape. Without the creation of tube amplifiers and heterodynes this task was insoluble, and there were no electron tubes in Russia. The deadlines were extremely strict. And so, already by the end of 1914, the first Russian amplifier and generator tubes appeared, or, as they were then called, “cathode relays.” All the research work and all the technical development of these tubes were directly supervised by N. D. These tubes, which among users received the name “Papaleksi tubes,” had an enormous influence on the development of Russian radio engineering during the First World War.

N. D. also introduced a substantial improvement into the technology of tube manufacture, for the first time using high-frequency induction heating for outgassing their electrodes during evacuation. Few people know now that this first application of high-frequency heating belongs precisely to Nikolai Dmitrievich. In his archive there has been preserved from those days a piece of iron, the first in the world to be melted in vacuum by high frequency.

The creation of electron tubes made it possible immediately to develop low-frequency amplifiers and heterodynes, and with their aid to make direction-finding installations operating at a great distance from the front. All this work was likewise supervised by N. D. Subsequently, they were ...

special tube receivers intended for army and naval aviation were developed. N. D. himself tested these receivers on board an airplane. With the aid of powerful (kilowatt) “Papaléxi tubes,” and with N. D.’s direct participation, in 1915 radiotelephone communication was first carried out in Russia—between Tsarskoe Selo and Petrograd. In 1916, under N. D.’s direction, equipment for underwater telegraphy was developed, and investigations were carried out of radio communication between a shore station and a submerged submarine. In these experiments the dependence of the signal strength on the depth of submergence and on the wavelength was established. At the same time direction-finding from the submarine was also performed, since the antenna developed for it by N. D. was essentially a loop. N. D. himself sailed on the submarine and personally conducted the tests. In 1917 N. D. carried out experiments on telegraphy with undamped oscillations between Petrograd and a submarine located in Helsingfors, experiments on controlling submarines at a distance, and directed the development of powerful amplifiers for the remote control of airplanes.

Alongside this vigorous scientific and technical activity, N. D. also occupied himself with questions of theory. It was precisely in this period that he carried out an extensive investigation on the theory of the excitation of oscillations by means of electron tubes; however, it was published later, and its second part, in which the matching method was again successfully applied, remained altogether unpublished.

At the beginning of 1918 N. D. moved with the laboratory to Moscow. Here he took part in organizing the laboratory at its new location—at the Shabolovka radio station—but soon left for Poltava. There he received from L. I. Mandelstam an invitation to come to Odessa, which he followed in the autumn of that same year.

In Odessa N. D., together with L. I., set about, in the most energetic fashion, organizing—as he himself characterized it, from scratch—the Odessa Polytechnic Institute. Initially N. D. was an assistant professor in the Department of Physics at this Institute and head of the physics practicum, and from 1920 on, professor of theoretical electrical engineering. In addition to a course in theoretical electrical engineering, N. D. lectured on meteorology and on the theory of oscillations. Here he put into order and published the first part of his Petrograd investigation on the theory of the tube generator.

Alongside his extensive pedagogical and scientific work, N. D. did not abandon scientific and technical activity. From the summer of 1920 he served as scientific consultant to the Odessa State Radio Plant. In addition, he organized a vacuum laboratory at the Polytechnic Institute and, despite difficult conditions, established in it the production of receiving radio tubes. The personnel for this production consisted of a group of enthusiastic students, while the material resources were obtained from vodka bottles and ordinary electric light bulbs.

...filaments. And yet production was set up, above all thanks to the technical inventiveness and acumen of N. D.

All this extensive and varied activity seems utterly astonishing if one takes into account that N. D.’s health was then in an extremely serious condition. As a result of hardship and poor nutrition he developed tuberculosis of the glands, and the doctor predicted that he had only a month to live. The care of students, who procured additional rations for N. D. and arranged a trip to a sanatorium, as well as N. D.’s own athletic hardening, enabled him to overcome this illness. N. D. was an excellent sportsman—an alpinist, skater, cyclist, and lover of skiing from the very first days of its coming into fashion.

N. D.’s love of sport was combined with a deep love of nature, especially of mountains and the sea. When he found himself in beautiful places, he was entirely transformed. The greatest pleasure for him and the best rest were excursions, and above all excursions in the mountains. Already in Strasbourg, whenever possible, he would go off at least for a day or two into the mountains, and subsequently, right up to 1939, he spent every summer in the mountains, making ascents and astonishing the young with his endurance and his ability to walk.

All the years of their stay in Odessa, N. D. and L. I. Mandelstam spent together; together, in 1922, they moved—as scientific consultants of the radio laboratory of the Trust of Low-Current Factories—to Moscow, and then in 1924 to Leningrad, since the Administration of the trust moved there. At that time the laboratory was transformed into what is widely known among us as the Central Radio Laboratory (CRL).

N. D. himself characterizes the CRL period of his joint scientific work with L. I. Mandelstam as the period that brought the most significant results in the field of radiophysics and radio engineering. During the first half of this period N. D. was almost every year (in 1923, 1926, 1927, 1928) sent abroad by the trust—to Germany and France. In view of those possibilities for personal contact which N. D. possessed thanks to his broad reputation in foreign scientific circles, these trips played, from the point of view of scientific and technical information, a very great role. In addition to his old connections with Strasbourg scientists and representatives of “Telefunken,” N. D. was personally acquainted with such leaders of radio engineering and the theory of oscillations as Barkhausen, van der Pol, Mène, and Le Corbeiller. Despite N. D.’s repeated absences during this first half of the CRL period, a whole series of important developments had already been carried out, among which may be named new methods of radiotelegraph and radiotelephone modulation, new methods of high-frequency measurements, in particular measurements of modulation depth and measurements of the effective values of the parameters of electric circuits, a device for quartz stabilization of frequency, a highly selective receiver with a quartz filter, a new method of regeneration, and a number of others. For illustra-

In order to assess the degree to which these developments were new and, at times, even unexpected, it is perhaps worth pausing briefly on at least one of them—for example, on the radiotelegraph keying device developed as early as 1924.

The powerful stations of that time consisted of a single-stage self-excited generator, to which powers were supplied, for example, of 45 kW, with the power in the antenna reaching 20–25 kW. In telegraph keying this large power was controlled by contactors connected into the tube grid; these operated with incredible noise and crackling, with the formation of an arc because of high radio-frequency voltages and, accordingly, with the use of ventilators. On the basis of drawings received from France, the trust was then developing a powerful transmitter for the Tehran radio station, and telegraph keying proved to be the weak point of the entire apparatus. N. D. proposed a magnetic keying device based on the saturation of iron. Instead of mechanical contacts, he installed a small box, inside which a small choke was placed in oil. Clearly and faultlessly, without any noise or moving parts, this keying device controlled a power of 25 kW, operating from a six-volt accumulator and consuming only 50 W. The impression produced by this novelty on radio engineers was enormous. Subsequently E. Ya. Shchegolev used the magnetic keying device on two large ships of the navy, and only, approximately, from 1928 did this apparatus lose its importance, since multistage transmitters with a low-power master oscillator had been invented.

E. Ya. Shchegolev cited this episode in his recollections of L. I. Mandelstam. Who, then, was the author of this invention? The best answer to all questions of this kind may be provided by the words of L. I. Mandelstam himself, written by him in 1938 in a characterization of N. D.: “Our collaboration in the field of electromagnetic oscillations has continued for more than 30 years. During this long period, in our joint work in this field, such close contact has been established both with respect to initiative and to the development of problems (theoretical and experimental) that in most cases it is difficult to indicate what was done by one or the other. As for the technical realization of the results obtained in these works, the principal role belongs to N. D.”

Especially fruitful and significant in its results was the second half of the TsRL period, i.e., the years from 1929 to 1935. In addition to TsRL, N. D. also worked at that time at the Leningrad Electrophysical Institute (LEFI), where from 1926 to 1935 he headed the department of scientific radio engineering. To this period belong the intensive general development of the theory of nonlinear oscillations, the discovery of resonance of the second kind and of asynchronous excitation, the development of the theory of parametric excitation of oscillations, and the creation of interferen-

methods for investigating the propagation of radio waves. In these same years, or beginning with them, practical applications of these fundamental scientific results were developed: a receiving device with the so-called parametric filter was created; the first models of parametric machines—fundamentally new alternating-current generators—were built; the foundations were laid for a new field of application of radio—interference radio range-finding—which opened broad prospects for geodesy, hydrography, and navigation.

With regard to all these remarkable results, L. I. Mandelstam always especially emphasized the role of N. D. And indeed, there can hardly be any doubt that without N. D. all the new ideas listed—if they had arisen at all—would most likely have remained brilliant ideas, would not have taken on flesh and blood, and would not have received the thorough theoretical and experimental development and the practical extension that in fact were given to them.

The second half of the TsRL period mainly coincides with a new major stage in N. D.’s pedagogical activity. From 1926 to 1935 he taught at the Leningrad Polytechnic (subsequently Industrial) Institute, at first as a docent and then as a professor. He gave lecture courses on the physics of vacuum, on thermionic devices, and conducted seminars on special problems of radio engineering (generation and modulation, propagation of radio waves), which attracted both professors and instructors. Later N. D. conducted at the LEFI a seminar on nonlinear oscillations and parametric resonance. His teaching was thus closely connected with the most vital questions of current scientific research. Devotion to his work and a sense of responsibility never left N. D. in his pedagogical work as well. His punctuality was exemplary. The tram-service breakdowns that not infrequently occurred could not stop him. From the Petrograd side, across the Neva ice, he would come on foot to Lesnoe, to the Polytechnic Institute, but he never missed lectures or classes.

In addition to scientific and pedagogical work, N. D. also bore scientific-public responsibilities, to which he always applied himself with the greatest attention and seriousness. In 1929 he was elected deputy chairman of the Physico-Chemical Society at Leningrad University, and a year later chairman of the Physics Section and president of that society. By this time his name already enjoyed the widest renown and had entered textbooks both in our country and abroad. In 1931 N. D. was elected a corresponding member of the Academy of Sciences of the USSR, and this direct connection with the Academy soon played a very positive role.

In 1932 N. D. went abroad for the last time, on assignment from the All-Union Electrotechnical Association. He delivered two reports on Soviet research in the field of nonlinear oscillations at the so-called “narrow” First International

conferences on nonlinear oscillations held in Paris. At the invitation of H. D. van der Pol, N. D. also visited Holland at that time. It should be noted that, thanks mainly to the achievements of the nonlinear school of Mandelstam and Papaleksi, the center of research on the theory of nonlinear oscillations was already then in the Soviet Union.

At the Central Radio Laboratory, research was being conducted at this time on the recently discovered resonance of the second kind, on auto- and hetero-parametric excitation of oscillations, and on the radio-interference method. The generation of alternating currents by means of mechanical variation of parameters (initially machines with variable self-inductance, and then with variable capacitance) was being developed in N. D.’s laboratory at LEFI. By 1935, the most promising results had already been obtained in all these directions. The parametric principle of generation had passed beyond the laboratory stage, and the question arose of building technical prototypes of machines. The principal units of the radio-interference apparatus had been developed, and the entire method had undergone its first practical tests. In addition to continuous work at the experimental base in the town of Luga near Leningrad, two expeditions had already been carried out under N. D.’s direction and jointly with geodesists (TsNIIGAiK)—in 1934 to the Pyatigorsk region in the Caucasus and, in the spring of 1935, to Odessa. These expeditions confirmed the real practical value of the interference method, and the first measurements were made of the velocity of propagation of radio waves, as well as measurements of distances (from shore to ship).

One cannot but regret that organizational restructuring began at such a heated moment. In April 1935, the Laboratory of High-Frequency Physics of the Central Radio Laboratory, headed by N. D. and L. I. Mandelstam, was transferred, in connection with the reorganization of the Central Radio Laboratory, to LEFI and became part of the sector of nonlinear problems at LEFI. For nonlinear and radio-interference research this meant the loss of an extensive production base and exceptionally rich resources of measuring apparatus. Four months later, in connection with the reorganization of LEFI, N. D.’s laboratory was transferred to the research sector of LII, where N. D. was professor of the Department of Radiophysics. The possibilities for practical development narrowed still further. N. D. steadfastly endured these vicissitudes of fate and energetically sought ways to preserve and further develop the scientific directions whose significance was clear, apparently, to few. With regard to radio-interference research, the way out was the transfer of all the work to the Laboratory of Oscillations of the Physical Institute of the Academy of Sciences, which N. D. headed in 1935. Later, in 1938, the parametric machines found refuge in the Energy Institute of the Academy of Sciences, where N. D.’s laboratory was created for their development, consisting at first of one and then of two collaborators. From 1935 begins the final period of N. D.’s life and activity—the period of work in the Academy of Sciences.

With persistence and energy, with the unchanging endurance under which genuine scientific enthusiasm continued to burn, N. D. once again set to work.

As always, he did not confine himself to scientific work in the laboratories under his direction. In 1935 N. D. was appointed chairman of the technical physics group of the OTN; in 1937, chairman of the Special Commission of the Academy of Sciences of the USSR for the study of radio-wave propagation in the Arctic and for assistance to the expedition to the North Pole. From 1938, having finally moved to Moscow, he occupied the post of deputy chairman, and subsequently—after the death of L. I. Mandelstam—chairman of the All-Union Scientific Council on Radiophysics and Radio Engineering, organized under the Academy of Sciences of the USSR thanks to his and L. I.’s initiative and efforts.

In 1939 N. D. was elected a full member of the Academy of Sciences of the USSR.

The memory of the last years of N. D.’s life is still so fresh, they are so filled with events and with his own tireless and many-sided activity, that their illumination seems especially difficult. It is hard to speak of them as of the past also because the work and interests of N. D., which filled them, are still linked by many threads not only with today, but also with tomorrow.

The end of the TsRL period coincided with the drawing of a certain balance sheet of what had been done on nonlinear oscillations. At the suggestion of van der Pol, N. D. and L. I. Mandelstam, together with a number of coauthors, compiled a survey of the results obtained in this field and presented it as a report to the Congress of the International Scientific Radio Union (URSI), which took place in London in September 1934.*) In a considerably expanded form this survey was then published in 1936 under the title New Investigations of Nonlinear Oscillations.**) In the same year, for their work on nonlinear oscillations and on the propagation of radio waves, the Academy of Sciences of the USSR awarded N. D. and L. I. Mandelstam the first D. I. Mendeleev Prize. Further nonlinear investigations were carried out chiefly at the Scientific Research Institute of Physics of Moscow University (NIIF MGU) under L. I. Mandelstam and at the Gorky Research Physico-Technical Institute (GIFTI) under A. A. Andronov. The principal problems to which N. D. devoted himself were parametric generation of alternating currents and the propagation of radio waves. During the Patriotic War a number of tasks of a more special character were added to them, and after the war—questions connected with the propagation of radio waves in the ionosphere and with radio astronomy. This enumeration alone already shows how

*) L. Mandelstam, N. Papalexi, A. Andronov, S. Chaikin et A. Witt, Exposé des recherches récentes sur les oscillations non linéaires. Techn. Phys. USSR, 2, No. 2–3, 1 (1935).

**) Л. И. Мандельштам, Н. Д. Папалекси, А. А. Андронов, А. А. Витт, Г. С. Горелик, С. Э. Хайкин, Новые исследования нелинейных колебаний. State Publishing House for Radio Questions (1936).

wide was the range of purely scientific interests of N. D., and yet they by no means exhausted everything to which he devoted his energies.

From 1935 up to the beginning of the war, the development of the parametric principle of alternating-current generation advanced substantially. At LII, and then at ENIN, several models of parametric alternators were built, with powers from 300 W to 2–3 kW; the strengthening of insulation when operating under increased pressure (up to 12.5 atm) was tested with great success; parametric excitation at combination frequencies was obtained; reversal of the parametric alternator was carried out, i.e., its operation as an electric motor. N. D. gave the theory of such a motor and, in agreement with experiment, showed that the motor can rotate with an angular frequency equal to the difference between the frequency of the supply current and the natural frequency of the oscillatory circuit, as a result of which the rotational speed can vary smoothly with a change in the tuning of the circuit. N. D. persistently strove to create industrial prototypes of parametric machines as well, in particular a powerful (25-kilowatt) machine intended for electrothermy. However, the factory manufacture of this machine was delayed from year to year, its design had time to become obsolete, and then everything was disrupted by the war.

Laboratory development and research continued also during the evacuation of the Academy of Sciences. The operating characteristics of a single-phase generator were studied in the greatest detail, and methods for its engineering calculation were developed. The experiments confirmed the great advantages of the parametric machine as a source of power for radio stations. A small machine with a hand drive, supplying a quartz lamp, was sent to the front.

In recent years, on N. D.’s instructions, a number of further laboratory prototypes were made and tested; a large depth of modulation was obtained (in one of the machines—up to 76%); excitation of the second parametric resonance was obtained, and quite recently resonances of higher orders as well; a three-phase parametric alternator was built; the operation of parametric and ordinary synchronous motors powered by a parametric generator was investigated; and much else besides.

The results of this extensive scientific and technical research work, into which N. D. invested all his theoretical mastery and experimental skill, speak for themselves. From an original physical idea, parametric generation has turned into a technically mature principle capable of growing into a major branch of electrical engineering. Parametric machines have no commutator or rotor windings and, in the simplicity of their construction, surpass even the asynchronous motor. They are especially advantageous in the range of increased frequencies, possess remarkable operating characteristics, are not afraid of short circuits, and can supply simultaneously a set of voltages, as though combining in themselves an alternator and a sectionalized transformer. These features open before them a path into the most diverse fields of application. Devices requiring increased current frequency,

powering radio stations and X-ray installations, hardening, contact and arc electric welding—this is the first thing that can be named already now, relying not only on theoretical considerations but also on direct experimental verification.

However, in the matter of introducing parametric machines, up to the present time it has not yet been possible to achieve the success that would correspond to the enormous efforts expended by N. D. in order to give the whole work the proper scale. With the death of N. D., the further fate of this major contribution to our electrical engineering requires special attention and effective measures with respect to the production base and the organization of the work.

In the Oscillations Laboratory of the Lebedev Physical Institute, N. D. at once developed investigations on the propagation of radio waves. In these investigations two tasks were set. First, to measure the velocity of propagation of radio waves under actual conditions and to study those details of the phase structure of the field which can be revealed only by means of radio interference. Second, in those cases where the velocity of propagation may be regarded as known, to apply the interference method to the determination of distances between separated points—a problem that already has direct practical importance. Alongside major theoretical, experimental, and design work in the laboratory, the solution of these problems required systematic experiments under actual conditions. N. D. was the organizer of all the expeditions, which were conducted annually up to 1941. Here are the regions of these expeditions, beginning in the autumn of 1935: Lake Ilmen, Novorossiisk, the White Sea and the Kara Gates, Istra and Pavlov Posad near Moscow, the steppe region of Northern Crimea, the town of Pugachev in the Trans-Volga region. The first expeditions were conducted jointly with the LII; TsNIIGAiK participated in most of the expeditions, and in two—the Hydrographic Administration of the Main Directorate of the Northern Sea Route, which had become interested in radio range-finding from its very first steps. It cannot be left unmentioned that the Main Directorate of the Northern Sea Route, as a result of this, proved to be the first maritime organization that has for many years successfully employed interference range finders in its everyday navigational practice and has its own experienced personnel. Another keenly interested “consumer,” actively participating in the development of the whole matter from the moment of its inception, is TsNIIGAiK, which is developing and using the interference method as applied to geodetic and cartographic problems.

It is difficult to exaggerate the significance of the scientific results achieved. With an accuracy not surpassed up to the present time (to \(3 \cdot 10^{-4}\) over the sea and to \(6 \cdot 10^{-4}\) over level land), the velocity of propagation of radio waves was measured. An upper bound was determined for the possible mean value of the dispersion (not more than \(0.01\%\)). A clear picture of the entire process of propagation over the earth’s surface was created. The correct interpretation of Sommerfeld’s classical theory was established and uncovered

the inadequacy of the Zenneck conception of surface waves, which had prevailed earlier throughout almost the entire history of radio. But even this is not all. The scientific fruitfulness of the radio-interference method, on the one hand, and the demands put forward by radio range-finding, on the other, made it timely to solve a number of new theoretical problems; moreover, the formulation of many of them was stimulated directly by N. D. This includes the remarkable works carried out recently by Academician V. A. Fok, Academician M. A. Leontovich, Corresponding Member of the Academy of Sciences of the USSR G. A. Grinberg, and Prof. E. L. Feinberg. In these works the problem of the so-called coastal refraction was solved, new methods were created for treating the propagation of radio waves, combining practically sufficient accuracy with physical clarity and mathematical simplicity, and the problem of the diffraction of radio waves around the spherical earth was solved. Taken together, the experimental and theoretical works on the propagation of radio waves, both those carried out under the immediate direction of N. D. and L. I. Mandelstam and those that arose on the basis of, or in connection with, these investigations, constitute a major contribution to radiophysics and enjoy deserved recognition abroad*).

In 1942 N. D. (jointly with L. I. Mandelstam) was awarded the Stalin Prize, First Class, in physics for work in the field of the theory of oscillations and the propagation of radio waves.

During the Patriotic War, at the station of the Observatory (near Kazan), N. D. created an experimental base at which, among other developments undertaken on his initiative, a short-wave model of one variant of interference devices—a phase probe—was tested. Upon returning to Moscow, N. D. willingly responded to the proposal of the Hydrographic Directorate of the Navy to provide hydrographic work with the interference method of coordination. This was carried out by the Physical Institute of the Academy of Sciences jointly with TsNIIGAiK. The result was a substantial acceleration of the work and the overfulfillment of the program over the course of two navigation seasons. With N. D.’s closest participation and consultations, the first industrial prototype in the Soviet Union of a navigation device based on radio interference was created in one of the branch institutes; and—what may perhaps be no less important—a large body of practical experience was acquired by a group of qualified radio engineers.

Thanks to the bold and at the same time profoundly well-founded scientific innovation of N. D. and L. I. Mandelstam, the Soviet Union proved—

) The works of the prewar period are summarized in the collection of articles edited by Acad. L. I. Mandelstam and Acad. N. D. Papaleksi, The Latest Investigations of the Propagation of Radio Waves along the Earth’s Surface, State Publishing House for Technical-Theoretical Literature, 1945. Subsequent theoretical works will be included in the second special collection, which is at present being prepared for publication. See also L. I. Mandelstam and N. D. Papaleksi, “On the Velocity of Propagation of Radio Waves,” Izv. AN SSSR (physical series), 7*, No. 5, 145 (1943).

NIKOLAI DMITRIEVICH PAPALEKSI

…stood at the source of native radio-interferometric ranging and far outstripped foreign countries in this field, where analogous ideas began to be developed only during the war years. The development abroad of interference or phase methods of positioning shows that their significance there has been duly appreciated. In this light, the continuous and far-sighted efforts of N. D., directed toward the further broad introduction of radio interference, acquire special significance. Thanks to his purposeful activity, our technical thought in the field of phase ranging is today at the level of what has been achieved throughout the world, but no delay can be allowed in further practical development. For N. D. this was perfectly obvious even at a time when it seemed to many that radiolocation solved all navigational problems without exception; his foresight concerning the paths of technical progress never deceived N. D.

The invasion of our motherland by the German-fascist hordes shook N. D., but a deep confidence in the ultimate triumph of the Soviet country did not leave him for a moment. He was a true patriot in the very highest sense of the word. Throughout the entire war he worked with redoubled energy. In addition to directing laboratories at FIAN and ENIN, N. D. took an active part in the general planning of scientific-defense themes, carried out a reorganization of the Radio Council, convened a scientific session of the Radio Council, made a trip in the autumn of 1942 to distant Borovoe in order to visit L. I. Mandelstam and discuss with him questions of current work and plans for the future, actively participated in the conduct of the elections to the Academy of Sciences in 1943, delivered a number of scientific reports and, above all, wrote a book on radio interference, which even during the war appeared in two editions*).

One cannot fail to recall the lively interest with which N. D. studied international and military events, and the astonishing erudition and knowledge with which he spoke about the military situation.

The range of N. D.’s interests was in general astonishingly broad. He loved and knew literature well, both Russian and Western European. He loved poetry—especially the poems of Lermontov—and wrote poems himself. He was attracted by descriptions of nature and travel; he knew geography perfectly. Alongside this, N. D. was fond of detective novels, in which what interested him was the analysis of tangled situations. Already from the fifth class of gymnasium, N. D. began to play chess, seriously studied its theory and solved problems, and subscribed to a great deal of literature on chess. He retained an interest in meteorology, and all his co-workers remember the remarkably accurate weather forecasts that N. D. made not only for short periods, but also for a year ahead.

It is hardly necessary to say that for N. D. the death of L. I. Mandelstam was an especially heavy blow, from which he could not

) N. D. Papaleksi, Radio Interference and the Struggle Against It*, 2nd ed., State Publishing House of Technical-Theoretical Literature, Moscow–Leningrad, 1944.

carry on to the end of his days. And yet his unflagging sense of duty, his boundless devotion to science, did not let his hands fall. The victorious end of the war and the transition to peaceful labor meant for him the possibility of bringing new, broad plans to life. The last two years of N. D.’s life were likewise filled with uninterrupted labor and illuminated by scientific initiative, as were all the preceding forty years of his scientific activity. In 1945 the Government awarded N. D. the Order of Lenin for his outstanding services.

N. D. strove for the broadest possible development of research on the propagation of radio waves. He repeatedly pointed out that any radio methods for determining distances ultimately rest upon an insufficiently precise knowledge of the velocity of propagation. Bearing in mind an extensive program of measurements of this velocity for different wavelengths and under various natural conditions, N. D. undertook the organization in the Crimea of an experimental base. He went into all the details of this undertaking and personally visited the laboratory then being built in Alushta. He intended to use the Crimean base not only for studying the velocities of propagation of radio waves along the earth’s surface, but also for investigations of the ionosphere.

N. D. was extremely fascinated by the question of simultaneous optical location and radar location of the Moon. As early as 1942, when N. D. was in Borovoe with L. I. Mandelstam, they arrived at the idea that, with contemporary technical means, both methods of locating the Moon could be carried out. N. D. later performed a number of detailed calculations concerning the reflection of an electromagnetic pulse from the Moon, and delivered a report on this subject at a laboratory colloquium, which drew an extraordinarily large number of listeners and was received with particular animation. As is known, radar location of the Moon was carried out in America in 1945. But, even taking into account a possible interval between the conception and the execution of this experiment by the Americans, one may state that, with respect to scientific initiative, N. D. and L. I. Mandelstam preceded the Americans by three years.

Another, entirely new problem that also especially occupied N. D. in the last months of his life was the radio emission of the Sun and of cosmic space. N. D. saw in these phenomena the foundation for a new science—radio astronomy. At his suggestion, interesting theoretical investigations were carried out on the question of the emission of radio waves by the Sun. On his initiative as well, the Laboratory of Oscillations took part in a scientific expedition to Brazil, where on May 20 of that year there occurred a solar eclipse with an extremely long total phase. Alongside ionospheric investigations, the members of the expedition also carried out observations of solar radio emission; moreover, the gradual covering of the disk during the eclipse was, in N. D.’s view, to provide more detailed information on the distribution of “radio brightness.” N. D. was preparing personally to head this expedition and took the most active and direct part in its organization.

N. D. constantly emphasized that the central task in ultra-high-frequency radio engineering was the development of measurement methods. He drew a parallel with the state of affairs in which long-wave radio engineering had found itself in his youth, and recalled how difficult it had then been to solve metrological questions over which no one now gives any thought. He considered the development of measurement methods for ultra-high frequencies to be one of the main directions of the Laboratory of Oscillations.

N. D. worked on the realization of all these plans and ideas with enthusiasm, persistence, and such energy as though sixty-five years of life did not lie behind him. Not thinking of his own strength, he took upon himself a multitude of duties and tasks and, at the cost of great inner strain, managed to carry them all out. Once again he headed one of the commissions during the elections to the Academy of Sciences, held a session of the Radio Council in the city of Gorky, directed physics journals, devoting especially much attention to the physics series of the Proceedings of the Academy of Sciences of the USSR, and directed the colloquium of the Laboratory of Oscillations of the Physical Institute of the Academy of Sciences, which, thanks to N. D., gathered at its meetings a wide audience consisting not only of workers in the field of oscillations, but also of radio specialists, electricians, mechanics, and acousticians. In addition, N. D. headed the Commission for the publication of the works of L. I. Mandelstam, chaired the Commission for the Mandelstam Prizes for work in the field of radio, and was a member of the Commission for prizes for work in physics. N. D. never considered it possible for himself simply to “be listed” on one commission or another, showing here as well a deep sense of responsibility and attention to the work.

During the last two years of his life N. D. delivered ten major lectures. Three of them were dedicated to the memory of L. I. Mandelstam; others concerned current questions of ongoing work (radio observations during the eclipse of 1945, increasing the accuracy of radio-interference methods); still others had the character of broad generalizations which N. D. could make, relying on decades of his experience (on the scientific problems of modern radio, on the development of the theory of nonlinear oscillations). In addition, at the suggestion of van der Pol, N. D., together with a number of coauthors, again compiled a review for URSI, which was a continuation of the previous review and outlined the work on nonlinear oscillations carried out in the Soviet Union in the period since 1935. He also prepared, for his intended trip to Romania, an interesting report devoted to the evolution of the concept of resonance*).

In N. D.’s archive there has been preserved an enormous number of calculations and computations carried out by him during this same period for a large monograph on the parametric generation of alternating currents, which he and L. I. Mandelstam had conceived of writing while still meeting in Borovoe.

) See this issue of Uspekhi Fizicheskikh Nauk*, p. 447.

S. M. Rytov

On January 24 of this year, N. D. completed a major article, “On Nonlinear Oscillations,” for the jubilee collection dedicated to the thirtieth anniversary of Soviet power, and immediately set to further work on the biography of L. I. Mandelstam. He gave himself no respite, and until his last day the words “I must do...” never left his lips. N. D. did not manage to finish Mandelstam’s biography, just as he did not manage to complete or carry out many of the works he had begun and conceived—their course was cut short by his untimely death.

A man of exceptional modesty and kindness, a truly good person—such N. D. will remain in the memory of all who knew him.

An outstanding, many-sided scholar; a teacher who trained new cadres by word and personal example; a researcher who opened new paths in technology—such will N. D. enter the history of the science to which he gave his entire life.