MUTUAL IMPEDANCES OF PARALLEL WIRES 531 



and 



Z. = Z/«> + 2Zi (^-^^, - 6X^) 



-''-^Y^^-l^'-^Y^^-'^' 



iheve 



a \ cr 



APPENDIX* 



Production and Properties of Electric Field Intensities and 



Voltages 



This appendix gives a summary of certain points in fundamental 

 electromagnetic theory which are necessary for a thorough under- 

 standing of some portions of Part I of the paper. 



Precisely defined, "voltage" (W) means the line-integral of the 

 electric field intensity (-E) along a specified path (s) between two 

 specified points. ^^ Thus 



W = I Esds = I Eds. (1) 



= I Esds = j Eds. 



At any point, in a dielectric or in a conductor, the total electric 

 field intensity E is the resultant of a part Eq due to all charges and a 

 part Eu due to all currents; thus E = Eg -\- Eu. {Eg and £„ might 

 be called the "charge electric intensity" and the "current electric 

 intensity" respectively.) 



Precisely stated, the phrases "due to all charges" and "due to all 

 currents" have the same meanings respectively as in the formulations 

 of the "retarded scalar potential" ^ and the "retarded vector poten- 

 tial" A of electromagnetic theory, as summarized in the following 

 paragraphs. "All charges" and "all currents," respectively, include 

 polarization charges and polarization currents in a dielectric, thus 

 allowing (indirectly) for a specific inductive capacity of any specified 

 value. Furthermore, "all currents" include also such additional cur- 

 rents (current whirls) as would account for a magnetic permeability of 

 any specified value. On the other hand, displacement currents are not 

 included and should not be, for they do not play the role of true 



* This appendix relates to Part I. 



" The "electric field intensity" (or, briefly, "electric intensity") is often called the 

 "electric force." 



