926 
electrical force’). We shall take for this term 4 P, representing by 
P the dielectrical polarisation. In the formula mentioned in the 
cited treatise under (38) °) this modified value will then have to be 
taken under the sign of summation for the electrical force. Following 
the derivation further as it has been given in the treatise in $$ 49 
and 50, we find for the index of refraction ” outside the magnetic 
field : 
nl C 
EEN 5 Sab)... 2 TT 5 S 
n Jd Dn 
in which » represents the frequency of the considered light vibra- 
tions (number of vibrations in 22 seconds), rv, free frequencies, while 
the constants C are in connection with LoreNntz’s constants B through 
the relation *): 
Cs BM) =S Bey) — Bl2—) 
1 La eo 
and S is introduced by way of abbreviation for the sum Sos. 
Expressions for the magnetic rotation per unity of length are 
found from ihe values of the indices of refraction of circularly 
polarized light rays in the magnetic field by means of the known 
relation *) 
. 
= 5 (= eet) 
in which c denotes the velocity of light. 
For the values of n4 and ”__ we find in an analogous way as 
in § 57 of Lorentz’s treatise : 
n> = 1 9 Rix) 
+ oa S 2 Be ews S 
Tei Se si Say by OI ATR FANT Si (DE 
pigs 1540s pd) 
lt 9 BY) 
en ES! SS CS 
5 = = Saber — 3 FCN! Gon a 
De (pd) 
in which d” represent the magnetic displacements through the Znmman- 
effect. It follows from this that: 
peeve ass 
TTS oe ease 
Taking into account that n4 and n— differ only little from 2, 
and likewise S4 and S— little from S, we find: 
1) Lorentz, loc. cit. p. 228. 
2) loc. cit. p. 229. 
8) loc. cit. p. 236. 
4) loc. cit. p. 245. 
