384 HELL SVSTLM I ECHMCAL JOURNAL 



These formulas are directly deduciblc from the fact that the ap- 

 plied e.m.f., defined as zero for /<0 and E cos w/ for />(), can itself 

 be expressed as 



-7-COSC0/ \-\ / sm /A— . 



For important types of transmission systems, including the 

 periodically loaded line, these formulas have been successfully 

 dealt with and solutions of a satisfactory approximate character 

 obtained. For further details, the reader is referred to a paper on 

 "The Building-Up of Sinusoidal Currents in Long Periodically 

 Loaded Lines" (Bell System Technical Journal, October, 1924). 



The foregoing must conclude our very brief account of the Fourier 

 Integral and its applications in Electric Circuit theory; an adequate 

 treatment of this subject would require a treatise in itself, and is 

 beyond the scope of the present work. All that has been attempted 

 is to give a very brief introduction to its significance in physical 

 problems and a few of its outstanding applications in circuit theory. 

 The reader who is interested in pursuing this subject further is 

 referred to a paper by T. C. Fry on "The Solution of Circuit Prob- 

 lems" (Phys. Rev., Aug., 1919), which gives a rigorous discussion 

 of the solution of the Fourier Integral by contour integration, to- 

 gether with some general forms of solution of the circuit problem.^ 



^ It was planned to include in this paper a bibliography of the important papers 

 bearing on the Heaviside operational method. This, however, has not been com- 

 pleted, but plans call for its publication in the next issue. — Editor. 



