( 29 ) 
Integrating partially we get : 
— = a number of surface integrals 
df, df Ee Hi 07h 074 dy 0’ 0 a 07h 
Ni dt gent Oy? dede ry a dt\ dz? ‘5 Ow? Od a ail 
4 dh(O?h _ Oh df dy | , ‘9 
dt\ Oy? zt dw? Owdz Òyde \ SVT ed 
df. HR 
In the coefficient of a in the cubic-integral we have: 
Lt 
Oh dg ag 0 (0g oh ML Hs 
 Oadz Oxdy Ow Oy ey TE Se (20) 
ee df Og 1 
at least if we put, 5 ERA dn =, so if we neglect the systems in 
& y z 
oe ‚df 
which electric masses occur. So we get for the coefficient of dE the 
( 
LN d 
expression — ~— and for the cubic integral : 
V? ot 
1 ; df df 1 03 Oy d Op Oy dy 
Baer A ec) ys egg En Baie eee 
V2 dt dt? iz Kore: Vi? § dz Oy dt de Oy e dt 
df 
As at the absolutely reflecting walls [7] and therefore also | =| 
continue to be zero, the surface integrals disappear; so equation (13) 
is proved. 
The quantities g and xy which are introduced in order that the 
variation of the electric displacement and the magnetic induction may 
take place fluently, are defined as the sum of the squares of the 
components of the rotations of those vectors, if we disregard the 
coefficient mae — introduced in order that equation (18) may be satisfied. 
LO weve 
This seems to me the simplest definition for p and x. It might, 
òf 0g Oh 
however, appear that we are not yet sure that —, — am g 
: On Oy dz 
convenient values. In order to show that this is not the case, we 
will prove the following relations 
òf 2 òf 2 òf 2 
fe eek see ey d Hink 4 21 
4 Hf 6) Ge) : 5) ‘ i 
} 0a \? da\? da? 
rd el B EE eet (SD 
Per Tor zl) +65) JE , oe 
where again the brackets indicate that we have to take also the cor- 
