224 
MR. G. H. LIVENS ON THE 
and include the energies corresponding to these two parts in with the appropriate 
totals the formulae just obtained are somewhat simpler in form. The total kinetic 
energy will be now 
Srr J 
or 
where 
B= H' + 4ri+i5[P)g, 
c 
and the potential energy Is 
I (Bdl)-87r (Bdl') 
do 
or is 
where 
FJ+Stt |’(E(iT)+87rJ (E^F) 
do, 
jl (Ef^DV'h 
ly = Iv + p+F. 
477 
This, however, leaves out of account the term 
which, representing as it does the energy of local actions and reactions, may be 
assumed to be inoperative as regards general mechanical processes, and may in 
consequence be rejected altogether. 
In connexion with the discussions of the expressions for the internal energy of the 
material media it may be worth while emphasising the significance of the various 
terms in the expression for the forcive on the polarised material elements derived in 
the previous paragraph, especially the way in which the various terms arise and their 
dependence on the term 
Curl [PpJ 
in the complete current. Further, we may notice how the complete expression for the 
change of intrinsic energy per unit volume, viz., 
(E+ikB]gp) 
is derived, the latter term being due to the above-mentioned term m the current. 
