ABSTRACTS OF TECHNICAL ARTICLES 361 



Standardization of Noise Meters.^ R. G. McCurdy. A brief review 

 of the present status of standardization of noise meters and measure- 

 ments, and progress made to date by the technical committee on noise 

 meters and noise levels of the American Standards Association. 



A Rotating Mirror Oscilloscope.^ 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. 



SJiot Effect and Thermal Agitation in an Electron Current Limited by 

 Space Charge."^ 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. The 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. 

 The random emission produces shot noise which may be reduced by 

 the space charge surrounding the cathode, while the velocity dis- 

 tribution produces thermal noise and is dependent upon the tempera- 

 ture of the cathode. 



Although plausible theories of these effects have been given they 

 have never been checked by accurate experiments because of the 

 difficulties involved. By using two electrode tubes capable of pro- 

 ducing a large space charge such measurements have now been made 

 and are reported in this paper. 



Simple Theory of the Three-Electrode Vacuum Tube} H. A. Pidgeon. 

 The physical principles upon which the operation of the three-element 

 vacuum tube depends are presented in simple form and the terms 



^ Elec. Engg., January, 1935; Indus Standardization, January, 1935. 



3 Jour. S.M.P.E., December. 1934. 



* Physics, January, 1935. 



5 Jour. S.M.P.E., February, 1935. 



