FLUXES OF ENERGY IN THE ELECTROMAGNETIC FIELD. 
457 
Here ignore e 0 , K, and ignore the curl of the electric force, and we obtaii 
(152) in (151), 
H.BV.q — HE div q + T div q — 
3TV 
dt 
H.BV.q - T div q 
oT„ 
dt ’ 
L 
by using 
. (153) 
which represents the distortional activity (my form, not equating to zero the 
coefficients of curl q in its development). We can, therefore, derive the magnetic 
stress in the manner indicated, that is, from (150), with the special meaning of 8B/9 1 
later stated, and the ig norations or nullifications. 
In a similar manner, from the first circuital law (89), which may be written 
( T) 
curl (H - ho) = C + + (D div q - DV.q), . (154) 
we can, by ignoring the conduction current and the curl of the magnetic force, obtain 
- | (®U) = E.DV.q - U div q - .(155) 
v ct ot 
which represents the distortional acti vity of the electric stress. 
The difficulty here seems to me to make it evident d priori that (150), with the 
special reckoning of 8B /dt should represent the distortional activity ( plus rotational 
understood) ; this interesting property should, perhaps, rather be derived from the 
magnetic stress when obtained by a safe method. The same remark applies to the 
electric stress. Also, in (150) to (155) we overlook the Poyntjng flux. I am not 
sure how far this is intentional on Professor Hertz’s part, but its neglect does not 
seem to give a sufficiently comprehensive view of the subject. 
The complete expansion of the magnetic distortional activity is, in fact, 
0T 
H.BV.q — T div q — = Q 2 + T + div qT — HG 0 ;.(156) 
and similarly, that of the electric stress is 
r) FT 
E.DV.q - U div q — = Q x + U + div qU - EJ 0 .(157) 
c it 
It is the last term of (156) and the last term of (157), together, which bring in the 
Poynting flux. Thus, adding these equations, 
2aV 3 - ^(U, + T,i) = Q + U + T + div q (U + T) - (EJ 0 + HG 0 ), . . . (158) 
where 
MDCCCXCII.—A. 
(EJ n + HG,,) — (6 (I Jq + h 0 G () ) — div W; 
3 N 
059) 
