210 BELL SYSTEM TECHNICAL JOURNAL 



nickel. These experiments establish the fact that under certain 

 conditions moving electrons behave like trains of waves. In the 

 interaction of these waves with a single crystal the optical phenomena 

 of diffraction, reflection and refraction have been observed. Scientific 

 accounts of these experiments are contained in the following papers: 

 Nature, 119, 558 (1927); Phys. Rev., 30, 705 (1927); Proc. Nat. Acad. 

 Sci., 14, 317 (1928); Proc. Nat. Acad. Sci., 14, 619 (1928). Although 

 the present paper is of a popular nature it aims to be quite compre- 

 hensive. It attempts to represent the status of this series of experi- 

 ments in August 1928. 



Rubber Compression Testing Machine.^ C. L. Hippensteel. This 

 paper gives a brief account of a new compression test developed at the 

 Bell Telephone Laboratories for more reliably judging the ability of 

 rubber insulation on metallic conductors to withstand certain service 

 conditions to which it is subjected. A recording compression testing 

 machine, which has been built for applying the test, and typical 

 results are illustrated. Other possible test uses for the machine are 

 suggested. 



New Languages from Old — Ilotu Secrecy is Gained by the Inversion of 

 Speech Sounds.^ C. R. Keith. The inversion of speech sounds may 

 be accomplished with the aid of methods used in radio broadcasting 

 and in carrier telephony. Among the possible applications, it is 

 illustrative of methods used to achieve secrecy in electrical com- 

 munications. 



The character of speech sounds is determined by the frequencies and 

 amplitudes of the component waves into which the sound may be 

 resolved. The process of inversion consists efi^ectively in altering the 

 frequency distribution of these components so that low tones appear as 

 high tones, while high tones appear as low tones. To the untrained 

 observer, inverted speech is unintelligible, although the characteristic 

 cadence is preserved. Inversion of the frequency scale is produced by 

 modulating speech with a carrier wave which lies just above the highest 

 speech frequency which is to be transmitted, and selecting the lower 

 sideband. For practical reasons connected with undesired distortion, 

 it is more desirable to break up the modulating process into two 

 distinct steps. The original speech sounds may then be regained by 

 repeating the process which led to its inversion. 



^ India Rubber World, Sept. 1928, pp. 55-56. 



^ Scientific American, October 1928, pp. 310-311. 



