ARTICLES BY BELL SYSTEM AUTHORS 465 



All dimensional data have been normalized in terms of wavelength, and are 

 presented in convenient nomographic form. 



I' Microwaves and Sound. W. E. Kock.^ Physics Today, V. 3, pp. 20-25, 

 March, 1950. 



Abstract — A recent development shows that obstacle arrays, modeled 

 after the periodic structure of crystals, refract and focus not only electro- 

 magnetic waves, but sound waves as well. The behavior of periodic struc- 

 tures can be investigated by microwave and acoustic experiments on such 

 models. 



Interference Characteristics of Pulse-Time Modulation. E. R. Kretzmer.^ 

 I.R.E., Proc, V. 38, pp. 252-255, March, 1950. 



Abstract — The interference characteristics of pulse-time modulation are 

 analyzed mathematically and experimentally; particular forms examined 

 are pulse-duration and pulse-position modulation. Both two-station and two- 

 path interference are considered. Two-station interference is found to be 

 characterized by virtually complete predominance of the stronger signal, 

 and by noise of random character. Two-path interference, in the case of 

 single-channel pulse-duration modulation, generally permits fairly good re- 

 ception of speech and music signals. 



Electron Bombardment Conductivity in Diamond.* K. G. McKay. ^ Phys. 

 Rev., V. 77, pp. 816-825, March 15, 1950. 



Perception of Television Random Noise.* P. Mertz.^ References. S.M.P.E., 

 Jl., V. 54, pp. 8-34, January, 1950. 



Abstract — The perception of random noise in television has been clari- 

 fied by studying its analogy to graininess in photography. In a television 

 image the individual random noise grains are assumed analogous to photo- 

 graphic grains. Effective random noise power is obtained by cumulating 

 and weighting actual noise powers over the video frequencies with a weight- 

 ing function diminishing from unity toward increasing frequencies. These 

 check reasonably well with preliminary experiments. The paper includes an 

 analysis of the effect of changing the tone rendering and contrast of the 

 television image. 



Loudness Patterns — A New Approach.* W. A. Munson^ and M. B. Gard- 

 ner. ^ Acoustical Soc. Am., JL, V. 22, pp. 177-190, March, 1950. 



Bell System Participation in the Work of the A.S.A. H. S. Osborne.* 

 Bell Tel. Mag., V. 28, pp. 181-190, Winter, 1949-50. 



New Electronic Telegraph Regenerative Repeater.* B. Ostendorf, Jr.^ 

 Elec. Engg., V. 69, pp. 237-240, March, 1950. 



Correlation of Gieger Counter and Hall Effect Measurements in Alloys Con- 



* A reprint of this article may be obtained on request to the editor of the B. S.T.J. 



iB.T.L. 



3 A. T. & T. 



