310 



Prof. W. B. Morton on the 



The differential equation to the lines of the Poynting flux 



dr~Z 



gives as integral 



b\ C 2tt> 

 tos, a ■ 



X 

 C' + log. log.— , (18) 



. < COS a 

 2?rA L 



— Sill a 



<x~)} 



C and C are arbitrary constants. 



For points not between the wires the corresponding equa- 

 tions differ from these in having (b — 2r), (36 + 2r), and 

 (b+r) instead of the terms (b f 2r), (36 — 27-), and {b — r). 



In the actual case the constant A has a very large value, 

 say order 10 4 , in accordance with the fact that the lines of 

 electric force are very nearly perpendicular to the wires *. 

 In order to make visible the general form of the curves I have 

 plotted fig. 2 with the following values : — 



a = 45°, a=l, 6 = 100, \=360, 

 b\ 1 = 1 



27tA* V2~2* 



Fiff. 2. 



20 40 60 80 100 120 140 160 ISO 



* Sommerfeld, he. tit. p. 282. 



