Abstracts of Bell System Technical Papers 

 Not Appearing in this Journal 



Radioactivity.' A. F. Kovarik and L. W. McKeehan. This 

 review of progress in radioactivity forms one of a series of mono- 

 graphs prepared by committees of the National Research Council. 

 It outlines the experimental and theoretical advances in the subject 

 since 191(5, the date of the last compendium. The section headings 

 are: I. Introduction, II. Radioactive Transformations, III. Alpha- 

 Rays, IV. Beta-Rays, V. Gamma-Rays, \'I. Nuclear Structure and 

 Radioactive Processes, \TI. Radioactivity in Geology and Cos- 

 UKjlogy, VIII. The Effects of Radioactive Radiations upon Matter. 

 The references to periodical literature are particularly detailed. 



Echo Suppressors for Long Distance Telephone Circuits.- A. B. 

 Clark and R. C. M.-\thes. This paper gives a brief description of a 

 device which has been developed by the Bell System for suppressing 

 "echo" effects which may be encountered under certain conditions 

 in telephone circuits which are electrically very long. The device 

 has been given the name "echo suppressor" and consists of relays in 

 combination with vacuum tubes which are operated by the voice 

 currents so as to block the echoes without disturbing the main trans- 

 mission. 



A number of echo suppressors have been operated on commercial 

 telephone circuits for a considerable period, so that their practicability 

 has been demonstrated. 



The Telephone Transmission Unit} Dr. F. B. Jewett. The 

 adoption by the Bell System of the TU as a telephone transmission 

 unit aroused considerable active discussion in foreign circles, namely, 

 by Colonel Purves, Engineering Chief of the British Post Office 

 Department, and Dr. Breisig of the German Telephone Administra- 

 tion. In this short paper, Dr. Jewett explains certain words and 

 expressions which, when accurately defined, he believes will eliminate 

 misinterpretations such as seem to ha\e Kd to the (■oiitro\ersies over 

 the Bell System TU. 



Dr. Jewett also points out that the numerical size for a transmission 

 unit is controlled by two factors, first, the magnitude should be such 

 that computation is convenient, and second, the magnitude should 

 be such as to permit telephone engineers and operating people to most 



' Bulletin National Research Council, Vol. 10, p.irl 1, March, 192.S, 203 pages. 

 ' Journal A. 1. K. E., Vol. 44. page 618, 1925. 

 • London I-;icrlri<i.in, \'nl. 94, page 562, 1925 



508 



