We now turn to Maxwell's equations (19a), (19b), (20a), (20b), and introduce the notation:[10]
with the convention that
shall be equal to
. Then Maxwell's equations may be combined into the forms
as one can easily verify by substituting from (30a) and (31). Equations (32) and (33) have a tensor character, and are therefore co-variant with respect to Lorentz transformations, if the