Chronicle

Session of the Division of Physical and Mathematical Sciences of the USSR Academy of Sciences

At a regular session of the Division of Physical and Mathematical Sciences of the Academy of Sciences of the USSR, held on September 20, 1946, in the Moscow House of Scientists, 6 reports were heard.

Corresponding Member of the Academy of Sciences of the USSR G. S. Landsberg reported the results of an investigation, carried out by him jointly with Candidate of Physico-Mathematical Sciences F. S. Baryshanskaya, of the combinational scattering of light in hydroxides in connection with the problem of the hydrogen bond.

The hydrogen bond is caused by a partial “sharing” of the hydrogen atom belonging to the hydroxyl group OH of one molecule with the oxygen atom that is part of another molecule. Such “sharing” occurs only when the distance between the two oxygen atoms is less than a certain critical value. The energy of the hydrogen bond is, in order of magnitude, between the energy of a chemical bond and the energy of van der Waals intermolecular interaction.

Many years of investigations by the speaker and his collaborators of the combinational spectra of substances containing the hydroxyl group O—H, covering both the liquid and the vapor-like state at various temperatures and pressures (including critical ones), as well as solutions of various concentrations, have shown that the occurrence of a hydrogen bond is always manifested in the displacement and typical broadening of the combinational lines characteristic of the valence vibration O—H; moreover, the coexistence of a diffuse band and a sharp line indicates the coexistence of associated groups and individual molecules.

The role of the hydrogen bond in the crystalline structure of solid substances containing the O—H group had until now remained uninvestigated because of experimental difficulties connected with their opacity. The authors developed an original method that makes it possible (in diffusely reflected light) to obtain combinational scattering spectra of opaque solid substances that appear as highly dispersed powders.

This method made it possible to investigate the structure of the combinational O—H spectrum for a number of anhydrous hydroxides and their crystalline hydrates. A sharp difference in the spectra was found, expressed in the presence (in some cases) or absence (in other cases) of spectroscopic signs of the hydrogen bond. Comparison with crystallographic data obtained for some substances makes it possible to connect the observed presence or absence of the hydrogen bond with the distances between neighboring hydroxyl groups (smaller or larger than the critical value), which may be of interest for crystallographic analysis. This same method made it possible for the first time to investigate the hydrogen bond at low temperatures (down to 100° abs.). In doing so, a strong decrease in the width of the band with decreasing temperature was discovered, extending to the transformation of the band into sharp lines. The latter makes it possible to interpret the broadening of the combinational lines into a band as an effect caused by fluctuations of intermolecular distances (more precisely, the distance between two oxygens),

whereas the position of the pole is determined by the mean distance O—O. Certain quantitative estimates confirm this interpretation.

The theory of “sound and radio-wave propagation in a layer bounded by two half-spaces” was the subject of a report by Candidate of Physico-Mathematical Sciences L. M. Brekhovskikh.

It proves possible to formulate, in a uniform manner, the general equations and boundary conditions for the propagation of sound and radio waves from a point source placed in a layer. The solution of the problem reduces to the formulation of the law of decrease of sound pressure (electric field strength) with distance from the source and can be represented in the form of a definite integral.

The solution makes it possible to ascertain the limits of applicability of the widely used picture of imaginary sources, to investigate the so-called “Mints waves,” known in seismology, and also to answer a number of such questions as, for example, radio communication in the case of a transmitter and receiver located underground, reflection from regions of finite size, etc.

Comparison with experimental data for the propagation of sound in a sea of finite depth shows satisfactory agreement.

The study of polar motion up to the present time has been conducted exclusively on the basis of an analysis of oscillations of the latitudes of various points. Attempts to use azimuthal observations for this purpose were unsuccessful, since it did not seem possible to extract the motion of the pole from a series of local nonpolar causes that also affect the direction of the meridian.

At the same time, the question of applying azimuthal observations is of great importance, for simultaneous latitudinal and meridional observations at one point are equivalent to latitudinal observations for two points separated by 90° in longitude.

Candidate of Physico-Mathematical Sciences B. A. Orlov reported on the application, by him, of the method proposed by Corresponding Member of the Academy of Sciences of the USSR A. B. Orlov for separating polar changes from nonpolar ones in the analysis of latitudinal measurements, to the processing of azimuthal measurements of the meridian marks of the large Pulkovo transit instrument, obtained during observations of the catalogs in 1905, 1915, 1925, and 1930. As a result of the elimination of significant nonpolar changes (reaching one second of arc), the results of these observations gave excellent agreement with the results of latitudinal observations. (The mean deviation of the azimuth for each tenth of a year, read from the curve of observations, from the computed one proved to be ±0″.66, not exceeding the deviations obtained in latitudinal observations.)

In “The Fundamental Problems in the Study of the Solar Chromosphere and Corona during Total Solar Eclipses,” Prof. V. A. Krat pointed out the great drop in the solar corona and the anomalous excitation of atoms in the chromosphere. Observations do not yet make it possible to choose between the mechanisms proposed to explain them. On the basis of theoretical considerations, the speaker arrives at a certain dynamical model of the chromosphere and corona.

The rich material obtained by expeditions that observed total solar eclipses has still not been fully processed. Of particular importance for comprehensive observations of the solar corona and chromosphere are determinations of the extinction coefficient and the scattering indicatrix of the terrestrial atmosphere.

The results of the recent work of the State Astronomical Institute named after P. K. Shternberg on the study of the solar corona and chromosphere were reported in their papers by Candidates of Physico-Mathematical Sciences N. N. Pariiskii, E. Ya. Bugoslavskaya, and I. S. Shklovskii.

I. S. Shklovskii has constructed a new theory of high electron temperatures in the corona. According to this theory, the decisive factors are the processes of ionization by electron impacts and recombination of ions. The theory

shows that, at an electron temperature of \(700\,000^\circ\), 9- and 10-fold ionization proves most probable, while at a temperature of \(400\,000^\circ\)—12- and 13-fold ionization of iron atoms.

An estimate of the concentration of iron and nickel atoms in the corona, made on the basis of Grotrian’s observations, showed that the relative abundance of these elements and of hydrogen is almost the same as on the Sun. It has been shown that a necessary consequence of the identification of coronal lines by Edlén is the presence in the spectrum of the corona of hard radiation with a line spectrum. The intensity of this radiation is of the same order as that of the coronal lines, as a result of which it must affect the state of ionization in the chromosphere. This influence may possibly explain the anomalous ratio of the concentrations

\[ \frac{\mathrm{He}^{++}}{\mathrm{He}^{+}}. \]

An analysis of the mechanism of absorption of radio waves in the solar atmosphere made it possible to draw a number of conclusions concerning the long-wavelength radiation of the Sun. It was found that radiation in the “meter” range is due to the outer, relatively cold (\(T \sim 3500^\circ\)) corona. Natural oscillations of the plasma of the outer corona, arising under the action of the stream of corpuscles ejected by the underlying layers, explain the anomalous sporadic radiation of the Sun in the “decimeter” range. The chromosphere is responsible for the “centimeter” radiation.

N. N. Pariiskii obtained spectra of the solar corona with the aid of a nebular spectrograph. Fraunhofer lines were found on the spectrograms; their contours do not explain the simple Doppler effect. Apparently, sunlight scattered by slow particles is present in the glow of the corona. It has been shown that the observed Fraunhofer spectrum cannot be explained by diffraction at the lunar disk.

A number of elements have also been found in the inner corona (above 15,000 km). The work of E. Ya. Bugoslavskaya on the study of the structure of the solar corona has shown the identity of coronal forms in all eclipses (beginning with 1936). The determining factor is formations on the solar surface.

From the consideration of coronal forms the conclusion is drawn that there are electric and magnetic fields acting on coronal details up to considerable distances from the Sun. The author considers it necessary to carry out a differentiated study of the corona and to obtain the physical characteristics of its individual formations.

Engineer S. K. Popov spoke on “a new industrial method for growing corundum crystals.”

Verneuil’s method makes it possible to grow artificially single pear-shaped corundum crystals of various colored varieties (ruby, blue sapphire, corundum-leucosapphire, green sapphire, alexandrite, and others). The processing of such crystals is connected with a large consumption of diamond powder and with considerable losses of the material of the crystal itself. The new method makes it possible, with a simultaneous increase in productivity, to eliminate these defects by growing single crystals of synthetic corundum in the form of thin and long rods. This has been achieved through a radical technical improvement of the Verneuil method. At the same time, the problem has been solved of obtaining single crystals with a specified orientation of the crystallographic axes. The latter is particularly important because the mechanical properties of articles made of corundum depend most strongly on the orientation of the crystallographic axes in the article. No less important is the possibility of obtaining dark ruby, since, according to the technical standard existing in the USSR, watch jewels must be made from it. By the Verneuil method the manufacture of such rubies is impossible.