Abstracts of Recent Technical Papers from 

 Bell System Sources 



Cipher Printi)io I'eJegraph Systems for Secret Wire and Radio Tele- 

 graphic Communications. G. S. Vernam.^ This paper describes a 

 printing telegraph cipher system developed during the World War 

 for the use of the Signal Corps, U. S. Army. This system is so designed 

 that the messages are in secret form from the time they leave the 

 sender until they are deciphered automatically at the office of the 

 addressee. If copied while en route, the messages cannot be de- 

 ciphered by an enemy, even though he has full knowledge of the 

 methods and apparatus used. The operation of the equipment is 

 described, as well as the method of using it for sending messages by 

 wire, mail or radio. 



The paper also discusses the practical impossibility of preventing 

 the copying of messages, as by wire tapping, and the relative ad- 

 vantages of various codes and ciphers as regards speed, accuracy 

 and the secrecy of their messages. 



Methods of High Quality Recording and Reproducing of Music and 

 Speech Based on Telephone Research. J. P. Maxfield and H. C. 

 Harrison.^ The paper deals with an analysis of the general re- 

 quirements of recording and reproducing sound, with the nature of 

 the inherent limitations where mechanical records are used, and a 

 detailed description of a solution involving, first, the use of electrical 

 equipment for the purposes of recording and, second, the use of 

 mechanical equipment based on electric transmission methods for 

 reproducing. 



Probably the most useful feature of the paper is the complete 

 description of the application of electrical transmission theory to 

 mechanical transmission systems. A detailed analysis is made of the 

 analogies between the electrical and the mechanical systems. 



Electrical and Photo-Electric Properties of Thin Films of Rubidium 

 on Glass. Herbert E. Ives and A. L. Johnsrud.' Films which 

 spontaneously deposit on glass surfaces in a highly exhausted cell 

 containing rubidium are electrically conducting, and photo-electrically 

 active. A study of the photo-electric properties of a rubidium coated 



^ A I. E. E. Journal, Vol. 45, pp. 109-115, Feb., 1926. 

 2 A. /. E. E. Journal, Vol. 45, pp. 243-253, Mar., 1926. 

 ^ Astrophysical Journal, Vol. 52, pp. 309-319, Dec, 1925. 



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