750 BELL SYSTEM TECHNICAL JOURNAL 



5. Multicellular horn, 



6. Piston set in sphere. 



A Magnetic Field Strength Meter Employing the Hall Effect in Germanium. ^^ 

 G. L. Pearson. The instrument to be described measures magnetic field 

 strengths as determined from the Hall effect in germanium. The essential 

 parts of this instrument include a small germanium probe, and a panel type 

 microammeter calibrated directly in gauss. Its accuracy is ±2 percent at 

 fields between 100 and 8000 gauss. At higher fields the readings are too 

 low, the error amounting to 9 percent at 20,000 gauss. The chief advantages 

 of this instrument are: (a) small size and portability, (b) continuous reading 

 rather than ballistic as in ordinary field strength meters, and (c) a small 

 nonmagnetic probe with which one can search in very narrow gaps. 



The Representation of Vowels and their Movements}^ Ralph K. Potter 

 and Gordon E. Peterson. It is shown that movement of the major 

 resonances in the voiced sounds of speech may be represented by traces in 

 a three-dimensional graph. Apparently a great deal can be learned about 

 speech through investigation of such traces, and they suggest a new method 

 for vowel designation that is particularly adaptable to quantitative analysis. 



General Mobile Telephone System}^ H. I. Romnes and R. R. O'Connor. 

 The tremendous need for communication with ships, airplanes, trucks, tanks, 

 and other mobile units used in such large quantities during the war accel- 

 erated the development of practical mobile radiotelephone equipment for 

 use in the 30 to 200 megacycle range and emphasized the practicability and 

 usefulness of mobile telephone service. By the end of the war the art had 

 advanced sufficiently in the applications of these higher frequencies so that 

 it seemed practicable to provide telephone service to mobile units on a gen- 

 eral basis rather than limit it to safety and emergency services as had been 

 the case before the war. The Federal Communications Commission there- 

 fore made available a few frequencies for experiments in this field. In the 

 two years which have elapsed, the Bell System has made this service avail- 

 able on an experimental basis in more than 60 cities and about 100 more 

 systems are under construction. This paper describes the arrangements 

 used and outlines the experience obtained to date with this service. Im- 

 provements are being made constantly so that this must be regarded as an 

 interim report on a rapidly changing and expanding service. 



Interference between V ery-High-Frequency Radio Communication Circuits}^ 

 W. Rae Young, Jr. Interference between different radio circuits is an old 

 problem, one which in the past generally has been solved by trial and error 



1" Rev. Sci. Instruments, April 1948 (pp. 263-265) 



^^ Jour. Acous. Soc. America, July 1948 (pp. 528-535). 



« Trans. A. I.E. £., vol. 66, 1947 (1658-1666). 



" Proc. I. R. E., Waves and Electrons Section, July 1948 (pp. 923-930). 



