THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



NOVEMBER 1917. 



XXXVII. On the Flux of Energy in the Electrodynamic Field. 

 By G. H. Livens, The University, Sheffield *. 



1. A GENERAL theory of the .energy streaming in an 

 J\. electromagnetic field was first given by Poynting 

 on the basis of Maxwell's theory, but on the assumption 

 that the available magnetic or kinetic enjerg3 T of the field 

 was distributed throughout it with the density mi""/ 



►B 



~ f (RdB) 'c/ 



at any point where the magnetic conditions' "ai 

 by the force vector H and induction vector B. In this 

 theory it is shown, quite generally and without any 

 restrictions as to the nature of the matter occupying the 

 field, that the flux of energy at each point may be regarded 

 as determined completely by the vector 



wherein E denotes the vector of electric force intensity 

 at the point and c the velocity of radiation in vacuo. All 

 quantities are assumed to be measured in ordinary electro- 

 magnetic units and the notation is that usually adopted 

 to denote the vector product. 



This theory has been extensively developed by numerous 

 writers, and it is shown to lead to a very simple and plausible 

 explanation of the processes in operation in the electro- 

 magnetic field, both in the general case and in the particular 



* Communicated by Sir J. Larmor, F.R.S. 

 Phil Mag. S. 6. Vol. 34. No. 203. Nov. 1917. 2 E 



