  In 1973, Le Bellac and Levy-Leblond (Nuovo Cimento B 14, 217-234) discovered
that Maxwell's equations possess two non-relativistic Galilei-covariant limits,
corresponding to E >> cB (electric limit) or E << cB (magnetic limit). Here, we
provide a systematic, yet simple, derivation of these two limits based on a
dimensionless form of Maxwell's equations and an expansion of the electric and
magnetic fields in a power series of some small parameters. Using this
procedure, all previously known results are recovered in a natural and
unambiguous way. Some further extensions are also proposed.
