Abstracts of Technical Articles From Bell System Sources 



Reciprocal Theorems in Radio Communication} John R. Carson. 

 Two reciprocal theorems, the generalized Rayleigh theorem and the 

 Sommerfeld-Pfrang theorem, are of great theoretical importance in 

 radio communication. A careful analysis of these theorems and their 

 mathematical derivations shows that they are quite distinct and their 

 practical fields of application different. In particular it shows that 

 the Sommerfeld-Pfrang theorem labors under restrictions, implicit in 

 its mathematical derivation, which seriously limit its field of practical 

 applicability. 



Telephone Circuits for Program Transmission? F. A. Cowan. 

 Systems of telephone circuits which are extensively used in the 

 transmission of programs to broadcasting stations are described in 

 this paper. Certain stages in the development of these networks are 

 considered and the general requirements for satisfactory transmission 

 at the present time are enumerated. The arrangements of the net- 

 works as well as the procedures used in setting up and maintaining 

 them are discussed. 



Correlation of Directional Observations oj Atmospherics with Weather 

 Phenomena.^ S. W. Dean. This paper analyzes some data on the 

 direction of arrival of static at Houlton, Maine, obtained by means of 

 a recorder and a cathode ray radio direction finder; and points out 

 that in certain cases there is a relation between the direction of static 

 and the location of storm centers. Two cases are discussed in which 

 day by day bearings showed static sources in the direction of moving 

 storm centers. 



A Direct- Current Amplifier for Measuring Small Currents} J. M. 

 Eglin. a direct-current amplifier consisting essentially of a Wheat- 

 stone bridge, having the amplifying tube in one arm and a balancing 

 tube in another, has been described by P. I. Wold and by C. E. Wynn- 

 Williams. This circuit has now been developed to give a constant 

 amplification for currents in either direction up to 10,000 times 

 the lowest measurable value. The amplification and the lowest 



■• Proceedings of the Institute of Radio Engineers, Vol. 10, June, 1929, pp. 952-956. 

 ^A.I.E.E. Journal, July, 1929, pp. 538-542 (abridgment). 



^Proceedings of the Institute of Radio Engineers, Vol. 17, July, 1929, pp. 1185- 

 1191. 



* Journal of the Optical Societv of America and Review of Scientific Instninioits, 

 Vol. 18, May, 1929, pp. 393-402.' 



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