In the special frame some peculiarities can be revealed about orientations of electric and magnetic fields in the virtual or real eigenmodes, formed out of eigenvectors ♭ ( a ) l as of 4- potentials according to the standard rules e ( a ) m = i( k$_{4}$♭ ( a ) m − k$_{m}$♭ ( a ) 4 ) , h ( a ) m = i ε$_{mnl}$♭ ( a ) n k$_{l}$ . To this end let us write down the eigenvector ♭ (1) µ (8) (after normalizing it) and the basic vectors c ± µ (11), in the special frame: Naturally, the electric and magnetic fields in mode 1 are oriented in the same way as in the single-invariant external field: they both lie in the plane, orthogonal to the external 18 e (1) = k$_{0}$ k$_{⊥}$ | k$_{⊥}$ $_{|}$√ | k $^{2}$| k 2 0 − k 2 3 , h (1) = [ k$_{⊥}$ × ϵ ] k$_{3}$ | k$_{⊥}$ $_{|}$√ | k $^{2}$| k 2 0 − k 2 3 . (32) From the normalized expression in (31) for ♭ (1) ν we find for the electric and magnetic fields in mode 1: IV. ELECTROMAGNETIC FIELDS OF SMALL PERTURBATIONS OF THE BACKGROUND FIELD A. Polarization of eigenmodes