ABSTRACTS OF TKCIINICAI. ARTICLES 331 



types of circuits, bandwidths, bridging and terminating arrangements, 

 and general information concerning the provision of television circuits are 

 covered. 



Communication in the Presence of Noise} Claude E. Shannon. A 

 method is developed for representing any communication system geomet- 

 rically. Messages and the corresponding signals are points in two "func- 

 tion spaces," and the modulation process is a mapping of one space into 

 the other. Using this representation, a number of results in communication 

 theory are deduced concerning expansion and compression of bandwidth 

 and the threshold effect. Formulas are found for the maximum rate of 

 transmission of binary digits over a system when the signal is perturbed 

 by various types of noise. Some of the properties of "ideal" systems which 

 transmit at this maximum rate are discussed. The equivalent number of 

 binary digits per second for certain information sources is calculated. 



Earth Conduction EJJecls in Transmission Systems^ Erling D. Sunde. 

 Earth conduction problems are encountered in both communication and 

 power system engineering in connection with investigations of earth resis- 

 tivity, groundmg, corrosion of buried metallic structures, power system 

 impedances and fault currents, inductive interference, lightning disturb- 

 ances, and in connection with ground-wave radiation fields. Mr. Sunde 

 deals comprehensively with the theory underlying various earth conduction 

 eflfects and with its engineering applications, and brings together in unified 

 manner many topics that hitherto have received only separate discussion 

 in the Uterature. The author's purpose throughout has been to tie his 

 discussion to practical considerations and problems. 



Beginning with a review of the theory underlying various earth conduc- 

 tion effects and with its engineering applications, the book contains the 

 following chapter headings: basic electromagnetic concepts and equations, 

 earth resistivity testmg and analysis, resistance of grounding arrangements, 

 mutual impedance of insulated earth-return conductors, propagation 

 characteristics of earth-return conductors, d-c earth conduction and cor- 

 rosion protection, power system earth conduction and inductive inter- 

 ference, surge characteristics of earth-return conductors, lightning protec- 

 tion of cable and transmission lines. 



A carefully compiled bibliography is mcluded. 



^Proc. I. R. E., January 1949. 



» Published by D. VanNoslrand Company, Inc., New York, London and Toronto, 

 January, 1949. 373 pages. $6.00, 



