We know that light,
an electromagnetic wave, does propagate through glass, for example We
have seen earlier that the total electric and magnetic fields inside a
medium are described in terms of a permittivity e and a magnetic
permeability m (these describe the factors  by which the total fields differ
from the external fields) These replace e0 and m0 in the description to
electric and magnetic fields in Maxwell’s equations with the result that in
a material medium of permittivity e and magnetic permeability m, the
velocity of light becomes,
1
v
µε
=
(8 11)
Thus, the velocity of light depends on electric and magnetic properties of
the medium