From Current Literature

Multiple-cathode oscillograph. In the simultaneous recording of several electromagnetic processes by means of several cathode oscillographs there always arises the possibility of errors that are difficult to take into account, caused by random fluctuations of the accelerating voltage and of the field strength that produces the deflection of the electron beam along the time axis. To eliminate these errors, M. Knoll constructed a multiple oscillograph in which the electron beam, emerging from the cathode, is divided into separate parts by means of a diaphragm with several apertures; with the aid of a magnetic lens (a short coil, proposed by Busch and used by the author in an electron microscope), the separate beams are focused in the plane on which the curve is recorded. The deflection of the beams along the time axis is produced by a common electric or magnetic field; the accelerating voltage is likewise common to all beams, while the measured field is applied to each electron beam separately. A multiple oscillograph with four separate electron beams, almost no different in size from an ordinary cathode oscillograph, made it possible to record four processes simultaneously, and no distortions of the individual beams were observed (M. Knoll, E. T. Z. 53, 1101, 1932).

The electric “Warburg effect” in Rochelle salt. The process of electrization of Rochelle salt is known to be very reminiscent of the process of magnetization of a ferromagnet: “electric saturation” and a hysteresis loop are observed. The “Curie point” for Rochelle salt lies at about 23° C.

Kluge and Schönfeld placed a Rochelle-salt crystal between the plates of a capacitor that could be recharged, so that the field varied continuously from 800 to 880 cgs units. The discharge current was fed to a loudspeaker through an amplifier with a voltage amplification factor of 50,000. Noises were heard in the loudspeaker analogous to the Barkhausen noises that arise during the magnetization of iron, indicating that the process of electrization of Rochelle salt is accomplished by a reversal of individual formations within the crystal in the direction of the electric field. At temperatures above the Curie point the phenomenon disappears (M. Kluge u. Schönfeld, Naturwiss. 21, 194, 1933).

Generation of powerful sound oscillations by means of a magnetostrictive vibrator. By exciting magnetostrictive oscillations of a nickel rod, Gaines succeeded in obtaining such a large oscillation power that the rod broke apart. The rod was placed in a vessel of water, which cooled it during operation. With intense oscillations of the rod, a fountain up to 6 cm high formed on the surface of the water. Under the action of these powerful oscillations, destruction is observed in metal and glass immersed in the water. A test tube through which the oscillations are passed becomes charred inside. It is possible to obtain colloids from oil placed in water. Frogs, fish, and insect larvae placed in water penetrated by a beam of such oscillations perish. Bacteria die so quickly that, with the aid of the oscillations, it appears possible to sterilize milk. The author also succeeded in obtaining figures in a Kundt tube and in developing a theory of their formation (Newton Gaines, Physics, 3, 209—229, 1932).

Diffraction of light in ultrasonic waves propagating in a liquid. To study the propagation of ultrasonic waves in a liquid, Bär and Meyer used the phenomenon of diffraction of light rays propagating in the liquid perpendicular to the ultrasonic waves discovered by Biquard and Debye (see Usp. Fiz. Nauk, XIII, 1933). The authors directed a beam of light rays onto a screen in which a series of small round apertures had been made. The rays then passed through the liquid under investigation and fell on a photographic plate. The ultrasonic oscillations (frequency, 7.5 megahertz) were produced by a thin quartz plate. In the absence of oscillations, images of the apertures were obtained on the photographic plate; when the quartz was excited, a diffraction pattern appeared around the images of the apertures. By this method, whose value lies in the possibility of simultaneously studying a large region permeated by ultrasonic waves, it proved possible to investigate the distribution of the intensity of ultrasonic radiation in xylene and a mixture of vaseline and turpentine oils. In the latter case, owing to the high viscosity of the medium, strong attenuation was observed, interference upon reflection from a glass plate placed in the liquid was observed, and diffraction of the ultrasonic waves from a wire grating was observed; the latter observations made it possible to determine the wavelength and velocity of the ultrasonic waves, which turned out to be equal to about 1500 m/sec (R. Bär und E. Meyer, “Phys. Zs.,” 34, 393, 1933).

On an electric lens for an electron beam. An electron microscope with electric lenses was developed by Brüche and Johannson (“Naturwis.,” 21, 353, 1932; see also Usp. Fiz. Nauk, XIII, 1933). In new work Johannson and Scherzer give a detailed theory of a lens consisting of three electrodes, the two outer ones being at a common potential. The electrodes have holes for the electron beam to pass through, but they have no grids, which distort the images. The authors come to the conclusion that the principal quantity determining the focal length of such a lens is the ratio of the voltage on the lens to the voltage accelerating the electrons, and they confirm this conclusion experimentally by observing images obtained with simultaneous proportional reduction of both voltages, as well as in photographs taken at variable voltage. The images they obtain are very successful, but still inferior to photographs obtained by Knoll and Ruska with the aid of magnetic lenses (H. Johannson und O. Scherzer, “Z. Physik,” 80, 183, 1933; O. Scherzer, “Z. Physik,” 80, 193, 1933).

An attempt to detect neutrons in atmospheric air. To detect neutrons in the air, W. Meissner and K. Steiner compressed air by pumping out gaseous helium, in which neutrons should have remained. The helium was then liquefied, and the volume in which it had originally been located was artificially reduced. It could then be expected that the pressure of the neutron gas would increase in proportion to the decrease in volume. However, in the experiment this increase in pressure could not be detected, from which the authors conclude that the content of neutron gas in the atmosphere does not exceed \(1.6 \cdot 10^{-11}\) of the initial volume of air. The authors indicate, however, that the neutrons may have escaped from the volume under study through the glass walls of the vessel. Theoretical calculations by Swinne (R. Swinne, “Z. techn. Phys.,” 13, 279, 1932) give, for the upper limit of the possible neutron content in the atmosphere, a value of the order of \(10^{-10}\)—\(10^{-11}\) of the volume (W. Meissner und K. Steiner, “Z. Physik,” 80, 1, 1933).

N. Malov