212 BELL SYSTEM TECHNICAL JOURNAL 



Quality Control hy Sampling}^ W. L. Robertson. A discussion 

 of the application of the mathematical theory of sampling to com- 

 mercial shop inspection. Also gives tables illustrating numerically the 

 results obtained from the various sampling plans in use. 



Problems in Power Line Carrier Telephony and Recent Developments 

 to MeetThemP J. D. Sarros and W. V. Wolfe. Power transmission 

 lines as commonly encountered present relatively complex networks 

 having irregular and unstable attenuation-frequency characteristics 

 within the 50-150 K.C. band employed for power line carrier telephony. 

 The high frequency noise may be very high. 



A single side band carrier suppressed system operating on a single 

 frequency duplex basis has been developed to overcome these trans- 

 mission difficulties. 



A comparison of this system with other types shows its superiority. 



The initial installation of this equipment was made on the 220 K.V. 

 lines of the Pacific Gas and Electric Company. 



The Planning of Telephone Exchange Plants}^ W. B. Stephenson. 

 This paper discusses procedures followed in planning future extensions 

 to telephone exchange plants to care for increased demand for telephone 

 service. An outline is given of the methods employed in forecasting 

 future demand for telephone service and in determining the most 

 efficient design of the plant to meet the service requirements. The 

 uses made of engineering comparisons in solving the economic phases of 

 various kinds of telephone engineering problems are discussed, with 

 particular reference to location and size or extent of major items of 

 plant as well as the time when they should be ready to give service. 

 Emphasis is placed upon the importance of those factors less readily 

 evaluated, such as service factors, practicability from a construction 

 and operating standpoint, flexibility, etc. 



The Effect of the Acoustics of an Auditorium on the Interpretation of 

 Speech}^ E. C. Wente. Studies of speech sounds in the Bell Tele- 

 phone Laboratories have shown that 60 per cent of the acoustic 

 energy in speech lies below 500 c.p.s., although the intelligibility of 

 individual speech sounds is reduced by only 2 per cent if all the 



" Factory and Industrial Management, pp. 503-505, Sept. 1928; pp. 724-726, 

 Oct. 1928. 



'2 Journal of the A. I. E. E., October 1928, pp. 727-731 (abridgment). 

 " Journal of the A. I. E. E., July 1928, pp. 500-503 (abridgment). 

 1* The American Architect, August 20, 1928, pp. 259-261. 



