  The fundamental role of line geometry in the study of wave motion is first
introduced in the general context by way of the tangent planes to the
instantaneous wave surfaces, in which it is first observed that the possible
frequency-wave number 1-forms are typically constrained by a dispersion law
that is derived from a constitutive law by way of the field equations. After a
general review of the basic concepts that relate to quadratic line complexes,
these geometric notions are applied to the study of electromagnetic waves, in
particular.
