  Given a point S (the light position) in P^3 and an algebraic surface Z (the
mirror) of P^3, the caustic by reflection of Z from S is the Zariski closure of
the envelope of the reflected lines got by reflection of the incident lines
(Sm) on Z at m in Z. We use the ramification method to identify the caustic by
reflection with the Zariski closure of the image, by a rational map, of an
algebraic 2-covering space of Z. We also give a general formula for the degree
(with multiplicity) of caustics (by reflection) of algebraic surfaces.
