Electromagnetic Waves 



A Textbook* (530 pages, S7.50 net) by S. A. Schclkunoil, published by D. 

 Van Nostrand, Inc., New York City, 1943. 



'TT^HIS new addition to a well-known series has been awaited with much 



-*■ interest by all those acquainted with Dr. Schelkunoff's contributions to 

 propagation theory, and it will be found that their expectations have been 

 entirely fulfilled. This monumental piece of work is equally remarkable for 

 the originality and consistency of its approach as for the wealth of informa- 

 tion contained in its five hundred densely packed pages. 



The author's systematic use of the harmonic oscillation, with complex 

 variables and coefficients, is in line with the marvelous development which 

 has occurred in the communication field during the last fifty years. Alter- 

 nating current theory, then acoustics, then vibrational mechanics succes- 

 sively dropped the differential equations which physics offered as a basis and 

 systematically restricted themselves to harmonic oscillations. This has 

 resulted in the replacement of the differential operator by iu, leading to a 

 tremendous simplification of steady-state analysis, which has been reduced 

 to the calculation of amplitude ratios and phase differences. The genuinely 

 difficult problems have not disappeared for all that but are now relegated to 

 Fourier or Laplace transform theory, and it has become apparent that an 

 enormous field of application can be covered by purely algebraic processes. 



Not the least advantage of this method has been the unification brought 

 into the three chapters of technical science mentioned above. Electrical 

 impedances gave the model after which acoustical and mechanical imped- 

 ances were fashioned; and mixed mutual impedances, thereafter, made it 

 possible to write the equations of electro-mechanical or acoustico-mechanical 

 transducers. There was an exciting era of intense development in this field 

 during the twenties; and it was amusing to hear at that time, and even a 

 good deal later, irate die-hards denouncing "impedances" with bitter irony 

 or viewing with alarm the spread of "analogies." 



Dr. Schelkunoff has set about to carry this point of view into Electromag- 

 netic Theory, and it may well be that his will be the honor of having brought 

 into the fold of harmonic oscillation theory the last chapter of Physics which 

 still had to be incorporated. (One might think of Optics, but of course half 

 of the book is really Optics.) Having given, in the first pages of his fourth 



*This review by P. Le Corbeiller is reprinted from Quarterly of Applied Mathematics, 

 Vol. 1, No. 2 by permission of the editors. Mr. Le Corbeiller, until coming to the 

 United States where he has joined the faculty of Harvard University, was an engineer 

 with the Administration Franfaise des Postes, Telegraphes et Telephones. 



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