870 
19. Let us solve n in terms of mandk. Referring to the equation 
of § 16.2 we must notice that 
MD == = Wa Dj = Vijn Û SN U Zn De =d 
and we get 
c? nr = Wy (em- + ke + [n- w]-) — wz (em, + ky + [n- wlj) 
or 
en=([w.(cm+ k + [n. w)) J. (19.1) 
From this it is easily seen that 
(a. w) = 0, 
and as 
[w.[n.w]] = wn — w(n. Ww), 
we get 
w. (cm +k) | 
zy; = Vg AM *4 == DEE a.So. (19.2) 
w 
¢? (2 = == 
C 
and 
5 z 5 . (c k 
Vonne Ee AC eo (19.3) 
’ 
w? ‘ w? 
I= GU — — 
(a c? 
In this form our result for the magnetization tensor can be readily 
compared with the corresponding formulae of Born '). He also points 
out the existence of the vector n and states that it is the magnetic 
analogon to the ROnteun-vector. We see that the factor 1/(1—w?/c’) 
disturbs the analogy. The difference in the appreciation of the result 
is this that Born (apart from not separating k) takes the whole of 
the components VgM**, wgM* and gM" to be the components of 
magnetization and seems not to have become aware of the fact that 
they contain the Rénreen-vector components belonging to n as well 
as the magnetization components proper. 
Born emphasizes the complete symmetry of his electric and mag- 
netic equations and certainly one can enjoy the mathematical beauty 
of the formulae thus written. It would, however, be erroneous to 
believe that the difference from Lorentz’ equations is more than a 
difference in form. Our investigation shows that the physical contents 
of Born’s equations is no other than what has been expressed by 
LORENTZ. 
Action of Polarization of Moving Magnetism. 
20. Let us illustrate some effects of n by considering a long 
1) Le. form. 39 and 39’, pp. 546 and 547. 
