Media for a Steady Flax having a Potential. 225 



Since log k — — logp, where p is the resistivity of a medium, 

 we also have 



log p = Pl log p 1 + (1 -px) log p 2 



= logp 2 +p 1 log& (3) 



P2 



as the relation between the resistivity of the mixture and 

 the resistivities and relative volumes of its constituents. 



If more than two media are present in volumes p i} p 2 , p$, 

 &c. per c.c. of the mixture, 



k = k^ . Jc 2 p* . kg* (4) 



In order to show the principal features of the distribution 

 of the flux and potential in a medium consisting of equal 

 square prisms of two media arranged as indicated in fig. 1, 

 the equipotential lines (or the stream-lines) for the single 



Fig. 4. 



D 



block considered above are shown in fig. 4, and for a strip of 

 the medium in fiV 5. In each case one constituent conducts 



Phil. May. S. 5. Vol. 49. No. 297. Feb. 1900. 



Q 



