Abstracts of Bell System Technical Papers Not 

 Appearing in this Journal 



Effect of Groimding on Telephone Interference} J. J. Pilliod. This 

 paper, presented before the Pittsburgh Section of the Association of 

 Iron and Steel Electrical Engineers in February 1928, is a rather 

 complete although non-mathematical presentation of the inductive 

 effects of power lines on nearby communication circuits. The produc- 

 tion of noise on the latter circuits and the production of voltages 

 sufficiently high to be prejudicial to the operators and users of these 

 circuits are separately discussed. Comparisons are drawn between the 

 inductive action of grounded and ungrounded power lines. Although 

 free from mathematics, the paper gives a very good outline of the 

 interference problem and points out the many opportunities presented 

 for cooperative effort both in connection with original design and with 

 reduction of interference on existing lines. 



A Modification of the Rayleigh Disk Method for Measuring Sound 

 Intensities.^ L. J. SiviAN. The usual procedure is to measure the 

 deflexion of the disk under the influence of a steady sound-field. This 

 paper outlines a procedure which has been found useful when the 

 sound amplitude can be made a suitable function of time. The scheme 

 depends on the fact that the torque which the sound-wave exerts on 

 the disk is a non-linear function of the sound amplitude, being propor- 

 tional to the square of the air particle velocity. The amplitude of the 

 sound-wave to be measured is modulated with a frequency equal to 

 that of the free vibration of the suspended disk. The measurement 

 requires reading the amplitude of oscillations corresponding to the 

 modulating frequency, rather than a steady deflexion of the disk. 

 The disturbances caused by spurious air currents are largely reduced. 

 In addition, in many practical cases at least, there is a gain in absolute 

 sensitivity. Both theory and experimental verification are given. 



Reflection of Electrons by a Crystal of Nickel.^ C. J. Davisson and 

 L. H. Germer. This is a report of some preliminary results obtained 

 in a new series of experiments in which a beam of electrons exhibits 

 the properties of a beam of waves. In previous experiments {Phys. 

 Rev., 30, 705, 1927) a beam of electrons was directed at normal inci- 



» Iron and Steel Engineer, Vol. V, pages 147-155, April 1928. 



2 The London, Edinburgh, and Dublin Philosophical Magazine, and Journal of 

 Science, Vol. 5, No. 29, March 1928, pp. 615-620. 



^Proceedings of the National Academy of Sciences, April 15, 1928, Vol. 14, No. 4, 

 pp. 317-322. 



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