894 
not displaced; so that in the integration over S the last term of 
both equations vanishes. Therefore it may omitted, and we obtain 
0 /oL . 
LVJ = — = = 2) . dg; 
ik 
dL, Vg = Wi dj’ ni (qbi a gib) wid; 
Sis found v (9 (Ymu—Yam) gk gi 
dik 
If we put 
qatqva = Wat gies Sige a) a 
gen ge Way = wr? 
we have 
Dm a Se ee 
OL, ' 
~ Vg en Va pr: 
Ogi 
And the variation principle gives 
sand 
TEELEN OEE 
Vg 
d a ki 
D= IE ot gue aes cee eee (C) 
OvK 
From Was a new tensor can be derived: 
ee Te when u =|= v ree = 
( 
The uw',r’ represent just the two other indices than u,v, in this 
way, that w,r,u',r' may be brougkt into the order 1, 2, 3, 4 by an 
even number of permutations. 
. According to, (A) we have 
In order to find the tension-energy tensor we shall proceed as 
Prof. Lorentz does. We calculate the left side of I for the case 
that the whole electro-magnetic field and the charges are displaced 
over a constant distance dre in the direction 2. By using (B) and 
(C) we find from (1) and (2) 
0 RAE det 
0 ‚ Ow? 
The term — (w? gc) may be transformed into qe 
Oxy ; x5 
+ Wi da, the 
