References

1. Uspekhi fizich. nauk XIII, 783, 1933.
2. Debye, Proc. Nat. Acad. Am. 18, 409, 1932.
3. E. Hiedemann and A. Asbach, Phys. Z. 34, 393, 1933.
4. Schaffer and Bergmann, Sitzungsber. d. Preuss Akad. Wiss. X, 152, 1934.
5. Schaffer and Bergmann, Naturwiss. 22, 685, 1934.

L. Groshev

Optical Evidence of Piezoquartz Oscillations at Overtones

By exciting piezoquartz with a variable wavelength and observing the formation of a diffraction pattern when a light beam is passed through a periodically distributed system of ultrasonic waves, by Debye’s method the author has demonstrated the excitability of quartz overtones (up to the 69th order). Measuring the distance between spectra and calculating from it and the frequency of the oscillations, measured with a wavemeter, the velocity of ultrasonic oscillations in a liquid, the author found that it is constant in the frequency interval from \(3.65 \cdot 10^5\) to \(2.5 \cdot 10^7\) hertz (for toluene). In an analogous manner the velocities of ultrasound in water, aqueous NaCl solutions, and chloroform were measured, and data were obtained that correspond to the data of other authors.

N. Malov

Investigation of Quartz Oscillations with an Optical Interferometer

To determine the distribution of nodal lines and antinodes on the surface of oscillating quartz, Osterberg (Osterberg, Phys. Rev. 43, 819, 1933) used a quartz plate as one mirror of an interferometer, placing it at a slight distance from the other mirror. In the absence of oscillations, parallel interference fringes were obtained, which separated into individual sections when quartz oscillations were excited in a direction perpendicular to its surface. With such an arrangement it was impossible to obtain complete nodal lines. Therefore Straubel (H. Straubel, Phys. Z. 34, 894, 1933) placed the quartz strictly parallel to the interferometer mirror, and in the absence of oscillations the entire field of view was dark. When oscillations were excited, the nodal lines remained dark, while the moving regions became bright. By this method, studies are being made of oscillations of plates of various orientation, size, and shape, the preliminary results of which are given in the cited work.

N. Malov

Frequency Control by Means of a Single-Filament Electrometer

To control the constancy of the frequency of alternating current, an ohmic resistance and a capacitance are connected in series into the circuit, their magnitudes being selected so that the voltage drops across both at the given frequency are equal. The filament of a single-filament electrometer is connected to the common point of the resistance and capacitance, and the electrometer legs are connected to the opposite ends of the resistance and capacitance. In this arrangement the filament is set in a certain position, which it can leave when the distribution of voltage across the resistance and the capacitor changes as a result of changes in the current frequency. It can be shown that the deflection of the filament is proportional to the change in frequency, so long as these changes are small relative to the magnitude of the original frequency (C. Hagen, Z. techn. Phys. 15, 231, 1934).

N. Malov