A New System for Measuring Currents Using a Cathode-Ray Oscilloscope. Until recently cathode-ray oscillographs—especially those with a cold cathode and a high accelerating voltage—were almost never used for the direct recording of current curves, since the self-inductance of the deflecting coil and its own period, with a constant sensitivity, proved too large, making it impossible to record rapid processes. At Matthias’s suggestion, a coil was constructed for recording current, placed directly inside the oscillograph and consisting of a single turn—in the form of a trapezoid—of copper strip. In the smaller base of the trapezoid there was an opening for admitting the electron beam, and in the lower part a slot serving for the exit of the deflected beam. The self-inductance of such a coil proved to be of the order of \(10^{-8}\) henry; the sensitivity at an accelerating voltage of 60 kV was \(0.165\ \mathrm{cm/AW}\). Recording current curves when a cable was short-circuited showed that processes having a duration of the order of \(10^{-8}\) sec are recorded without distortion. The authors also give calculation formulas for the coil described above, as well as for a multiturn coil (A. Matthias, B. v. Borries und E. Rucka, Zs. f. Physik 85, 336, 1933).

Investigation of Heated Cathodes Using an Electron Microscope. Using an electron microscope with electric lenses, Brüche and Johannson investigated the emission of a nickel surface on which barium vapors had been deposited in vacuum. The cathode was heated by thermionic radiation; a grid was first scratched onto the nickel for scale determination. The electron micrographs showed that at first strong emission occurs only from the scratches;

In addition, weak emission was observed from thin veins that had appeared here and there on the non-emitting surface of the cathode. After a short interval of time (at unchanged temperature) the emission of the veins ceased completely, the emission from the depression weakened considerably, and the entire surface of the cathode began to emit quite uniformly. This distribution of emission subsequently remained unchanged. In microscopic examination of the cathode surface, the presence of the veins could be detected only after etching the cathode surface. The authors consider the reasons for such peculiar behavior of the cathode to be as yet unexplained (E. Brüche and H. Johannson, Zs. f. Physik 84, 56, 1933).

Investigations of the ultrasonic field of vibrating piezoquartz. To investigate the ultrasonic field, Bücks and Müller used a heated Wollaston filament connected into one arm of a Wheatstone bridge; by moving the filament around the vibrating quartz (in air) and observing the change in its temperature under the action of ultrasonic waves, the authors were able to study the distribution of the radiation intensity near the quartz. By placing a reflector near the quartz, the authors obtained standing waves, whose wavelength (measured by the above-described method) proved to be in good agreement with the calculated values. Placing on the surface of the quartz a drop of an easily evaporating liquid (alcohol), the authors observed a number of very interesting phenomena: when the quartz vibrated, the drop was atomized, and in the resulting misty cloud the nodes and antinodes of the standing ultrasonic waves stood out very distinctly. After a short time, the cooling of the mist in the antinodes became so considerable that it condensed into small droplets (K. Bücks and H. Müller, Zs. f. Physik 84, 75, 1933).

Independently of the above-mentioned authors, Malov used an analogous method to investigate the ultrasonic field in oil; he determined the intensity distribution from the increase in the resistance of a thin wire caused by absorption of ultrasonic vibrations. He investigated the reflection and refraction of ultrasonic waves, studied the intensity distribution around quartz, and the influence of a diffraction grating on the intensity distribution; the velocity of ultrasonic vibrations measured by him for oil, water, and an aqueous solution of NaCl proved to agree with the results previously obtained by Loomis (N. Malov, Hochfrequ. u. Elektroakustik 42, No. 4, 1933).