Abstracts of Technical Articles from Bell System Sources (01 April 1935)

Standardization of Noise Meters.2 R . G . MCCURDY. A brief review of the present status of standardization of noise meters and measurements, and progress made to date by the technical committee on noise meters and noise levels of the American Standards Association. A Rotating Mirror Oscilloscope.3 R . F . MALLINA. When studying sound it is sometimes useful to project the wave-form of electrical or acoustical phenomena on a screen. A rotating mirror in combination with a vibrating mirror and a light source provide a convenient means of showing such waves. The problem of building an instrument for such a purpose is comparatively simple if a small screen is used in a dark chamber. However, when the screen is large enough to be viewed by a dozen or more persons, many difficulties arise. 

The paper describes how the various parts of the apparatus may be coordinated in order to produce a comparatively bright, clearly defined wave with a small incandescent lamp in a room of average illumination. The vibrator used in the apparatus may be so constructed that its response is either inversely proportional to or independent of the frequency. Shot Effect and Thermal Agitation in an Electron Current Limited by Space Charge.4 G. L. PEARSON. The space current in a thermionic vacuum tube is not a steady flow of electricity but is subject to minute irregular fluctuations. T h e two most fundamental causes for these fluctuations are the random distribution of instants of emission of the individual electrons and the distribution of these electrons in velocity.