464 BELL SYSTEM TECHNICAL JOURNAL 



Abstract — X'ariable and nonlinear systems are classified from the stand- 

 point of their significance in communication problems. Methods of solution 

 are reviewed and appropriate references are cited. The paper is a synopsis 

 of a talk given at the Symposium on Network Theory of the 1949 National 

 I.R.E. Convention. 



Some Early Long Distance Lines in the Far West. W. Blackford, Sr.* and 

 J. F. HuTTON." Bell Tel. Mag., \. 28, pp. 227-237, Winter, 1949-50. 



Radio Propagation Variations at VHF and UHF.* K. Bullington.* 

 LR.E., Proc., V. 38, pp. 27-32, January, 1950. 



Abstract — The variations of received signal with location (shadow losses) 

 and with time (fading) greatly affect both the usable service area and the 

 required geographical separation between co-channel stations. An empirical 

 method is given for estimating the magnitude of these variations at vhf and 

 uhf. These data indicate that the required separation between co-channel 

 stations is from 3 to 10 times the average radius of the usable coverage area, 

 and depends on the type of service and on the degree of reliability required. 

 The application of this method is illustrated by examples in the mobile 

 radiotelephone field. 



Speaking Machine of Wolfgang von Kempelen.* H. Dudley^ and T. H. 

 Tarnoczy. Acoustical Soc. Am., Jl., V. 22, pp. 151-166, March, 1950. 



Perception of Speech and Its Relation to Telephony. H. Fletcher^ and 

 R. H. Galt.' Acoustical Soc. Am., JL, V. 22, pp. 89-151, March, 1950. 



Abstract — This paper deals with the interpretation aspect and how it is 

 afifected when speech is transmitted through various kinds of telephone 

 systems. 



Vacuum Fusion Furnace for Analysis of Gases in Metals. W. G. Guldner^ 

 and A. L. Beach.^ Anal. Chem., V. 22, pp. 366-367, February, 1950. 



Complex Stressing of Polyethylene. I. L. Hopkins,^ W. O. Baker^ and 

 J. B. Howard.^ //. Applied Phys., V. 21, pp. 206-213, March, 1950. 



Noise Considerations in Sound-Recording Transmission Systems. F. L. 

 Hopper.2 References. S.M.P.E., JL, V. 54, pp. 129-139, February, 1950. 



Radiation Characteristics of Conical Horn Antennas.* A. P. King.^ LR.E., 

 Proc, V. 38, pp. 249-251, March, 1950. 



Abstract — This paper reports the measured radiation characteristics of 

 conical horns employing waveguide excitation. The experimentally derived 

 gains are in excellent agreement with the theoretical results (unpublished) 

 obtained by Gray and Schelkunoff. 



The gain and eflfective area is given for conical horns of arbitrary propor- 

 tions and the radiation patterns are included for horns of optimum design. 



*A reprint of this article mav he obtained on rei|uest to the editor of the B. S.T.J. 



•B.T.L. 



2W. E. Co. 



^Pac.T.&T. 



