  A new Fokker-Planck equation is developed for treating resonance line
scattering, especially relevant to the treatment of Lyman alpha in the early
universe. It is a "corrected" form of the equation of Rybicki & Dell'Antonio
that now obeys detailed balance, so that the approach to thermal equilibrium is
properly described. The new equation takes into account the energy changes due
to scattering off moving particles, the recoil term of Basko, and stimulated
scattering. One result is a surprising unification of the equation for
resonance line scattering and the Kompaneets equation. An improved energy
exchange formula due to resonance line scattering is derived. This formula is
compared to previous formulas of Madau, Meikson, & Rees (1997) and Chen &
Miralda-Escud\'e (2004).
