160 BELL SYSTEM TECHNICAL JOURNAL 



theory to vacuum tube circuits consists chiefly in giving special emphasis 

 to network design problems ordinarily found as part of vacuum tube am- 

 plifier design. The design of an over-all feedback loop is, of course, an 

 outstanding example. In addition, special attention is also given to the 

 design of such individual network units as input and output circuits, inter- 

 stage networks, and local feedback circuits, especially when they appear as 

 constituents of a broad-band amplifier. 



Judging Mica Quality Electrically.- K. G. Coutlee. A threatened 

 mica shortage resulting from an unprecedented wartime demand for mica 

 capacitors used in electronic communication equipment by the Armed 

 Forces was forestalled by rigid conservation measures, use of alternate 

 materials, and the use of electrically selected mica from types previously 

 considered unsuitable for capacitor use. By employing two electrical 

 tests, developed by Bell Telephone Laboratories, Inc. for the War Produc- 

 tion Board, in combination with visual and physical requirements, mica was 

 selected from plentiful stocks of lower visual quality types of mica, effec- 

 tively increasing the supply of capacitor mica by 60 per cent. This method 

 of electrically judging the quality of raw mica was given a thorough com- 

 mercial trial and found both practicable and reliable. 



A Simple Optical Method for the Synthesis and Evaluation of Television 

 Images.^ R. E. Graham and F. W. Reynolds. A combination of a 35- 

 millimeter motion-picture projector and a line screen enables the projection 

 of still or motion pictures closely similar in appearance to those produced by 

 television. This similarity of appearance is checked theoreticalUy by an 

 analysis of the type previously reported by Mertz and Gray in a discussion 

 of the theory of scanning. From the analysis it is shown that five para- 

 meters of the optical-simulation system may be varied to obtain the equiva- 

 lent of variations in television factors such as number of scanning lines, 

 size and configuration of scanning apertures, and width of frequency band. 



Photographs of simulated television pictures projected by this method are 

 presented. These pictures include subject matter of general interest as 

 well as as selected subjects to illustrate the spurious detail components in- 

 troduced by the television scanning process. These components produce 

 moire patterns, "steps" on diagonal lines, and impairment of vertical 

 resolution. Simulation pictures projected by this method have been com- 

 pared with those produced by a television S}'stem and the expected agree- 

 ment observed. 



Calculations are given of the diffraction effects in optical systems of this 

 type and it is shown that the departure from geometrical theory is small in 

 the arrangements described. 



^ Elec. Engg., Trans. Sec, November 1945. 



^Proc. I. R. E. and Waves and Electrons, January 1946 (pp. 18W-30W). 



