  It is shown that the axion concentrated in electroweak strings which are
consequently stabilized may produce a rotation of the polarization angle of
radiation from extragalactic sources larger than that caused by a background
field, and that axionic walls attached to global strings have an effect which
depends on the frequency. We discuss the validity of the classical and quantum
treatments of radiation and indicate that the latter produces conversion of
linear into circular polarization. We describe possible anomalies in the
observations which might suggest these influences of the axion.

Astrophysics;High Energy Physics - Phenomenology