October Session of the Department of Physical and Mathematical Sciences of the USSR Academy of Sciences

On October 21, 1946, a regular session of the Department of Physical and Mathematical Sciences of the USSR Academy of Sciences was held.

A report on the plan of scientific work of the Department for 1947 was delivered by Academician A. F. Ioffe. Pointing to the leading role of physics in modern natural science, A. F. Ioffe stated that, in accordance with the tasks set before Soviet science by the five-year plan, the Department’s plan for 1947 provides both for the development of major fundamental problems and for a number of works of direct national-economic importance.

One of the principal fundamental problems in 1947 remains the theoretical and experimental study of the structure of the atom, of matter, and of the nature of cosmic rays. It is planned to continue a comprehensive study of the properties of matter, with the aim of obtaining new substances and materials with specified properties. Research will continue on high-molecular compounds, crystalline substances, ferroelectric materials, the electrical strength of gases, etc., as well as the study of the properties of matter at low temperatures (superconductivity, superfluidity).

Much attention is being devoted to the problem of converting radiant energy, with a view to increasing the efficiency of devices used for this purpose. Further development will be given to studies in luminescence (especially of crystalline phosphors) and in the physics of semiconductors.

A significant place in the plan is occupied by theoretical and experimental work on the propagation of radio waves (including microwaves) and on the theory of nonlinear oscillations.

A number of works are devoted to the development of new methods of analysis.

In the field of geophysics, research will continue on all three envelopes of the Earth: the solid one (the study of the internal structure of the Earth’s crust, the development of geophysical methods for prospecting mineral resources), the liquid one (the thermics and dynamics of the sea), and the gaseous one (physical methods of investigation, atmospheric optics, radiant heat exchange, turbulence, problems of general circulation, the theory of climate, and weather forecasting).

Mathematicians will work on analytic methods in number theory, in the fields of algebra, topology, and probability theory, as well as on the aerodynamics of high speeds. Work on the theory of computing and solving devices is continuing.

The principal task of astronomers remains the restoration of the destroyed Pulkovo and Simeiz observatories and the completion of the processing of observations of the solar eclipse of 1945. Work will continue on the physics of the Sun and stars, the theory of perturbed motion, the time service, and other topics.

A report devoted to the centenary of the publication of Poiseuille’s work “On the Laminar Flow of Fluid through Tubes” was delivered by Doctor of Physical and Mathematical Sciences M. P. Volarovich. Briefly outlining Poiseuille’s life, the speaker dwelt in detail on the classic experiment that led Poiseuille to formulate the law named after him. The speaker emphasized that Poiseuille’s law, which serves as the basis for the hydrodynamics of laminar—

[[unclear: beginning of word]] flow, at the same time is the basic principle of viscometry, and more than 80% of work on the measurement of viscosity is carried out by the method of outflow from capillaries.

Academician V. G. Fesenkov spoke about his measurement of the height of the emission layer of the atmosphere. As is known, the nocturnal luminosity of the sky consists of the light of stars, zodiacal light, and the intrinsic glow of the upper layers of the atmosphere. Repeated determinations of the height of the emission layer have led to contradictory results, which may be explained by imperfections in the measurement methodology. One possible method for determining the height of the emission layer is to measure the brightness of the night sky at different zenith distances. The principal difficulty lies in the need to take into account the influence of the lower layers of the atmosphere on the measured brightness of the sky (extinction, air mass). The speaker proposed an original method that makes it possible to take this influence into account with sufficient accuracy and thus to isolate, in pure form, the component of the night-sky glow connected in its origin with the upper layers of the atmosphere. Application of this method to a series of observations made near the city of Alma-Ata yielded very close figures for the height of the emission layer—of the order of 280 km. The speaker believes that the results he obtained indicate that the glow of the sky is caused by an ionized layer \(F\).

The report by Doctor of Physical and Mathematical Sciences A. I. Shal’nikov and A. G. Meshkovsky on the experimental proof they obtained of the inhomogeneous structure of superconductors in the intermediate state aroused exceptional interest.

Landau had theoretically predicted that a superconductor in the intermediate state must consist of alternating superconducting and normal layers. The authors of the report undertook a study of the distribution of the field in a slit \((0.12\ \text{mm})\) of a single-crystal tin sphere 39 mm in diameter. The field meter was a bismuth strip \(5 \times 10 \times 250\ \mu\), mounted on a mica plate and moved along the slit. The field magnitude was recorded photographically on a moving strip. Measurements were made for two types of transition into the intermediate state: by increasing the magnetic-field intensity at constant temperature (below the critical temperature) and by lowering the temperature at constant field. In both cases a complex field structure was found, and the sequence of its distribution changed from experiment to experiment. However, if in the second case the distribution of regions resembled the alternation of superconducting and normal layers predicted by the theory, in the first case the picture was irregular and revealed the presence of a fine structure unresolved by the meter. The presence of the structure of the intermediate state proved possible to observe even with a large slit width: 0.3, 1, and even 2.3 mm, which proves the absence of a certain critical slit width, previously assumed to be necessary for the structure to emerge at the surface.

Studies with a wide slit also showed that magnetic lines of force are scattered inside the slit, which is fully explained by the difference in the behavior of large and small field meters.

Corresponding Member of the Ukrainian Academy of Sciences N. N. Bogolyubov gave an additional report on the theory of superfluidity presented by him on July 1, 1946. In the case of weak interaction between molecules, the weakly excited states of a gas may be represented as an ideal Bose–Einstein gas, consisting of certain “quasiparticles” corresponding to elementary excitations and not identified with molecules. The special form of the dependence of the energy of a “quasiparticle” on its momentum determines the property of superfluidity.