A moving dielectric appears to light as an effective gravitational field. A
t low flow velocities the dielectric acts on light in the same way as a mag
netic field acts on a charged matter wave. We develop in detail the geometr
ical optics of moving dispersionless media. We derive a Hamiltonian and a L
agrangian to describe ray propagation. We elucidate how the gravitational a
nd the magnetic models of light propagation are related to each other. Fina
lly, we study light propagation around a vortex flow. The vortex shows an o
ptical Aharonov-Bohm effect at large distances from the core, and, at short
er ranges, the vortex may resemble an optical black hole. [S1050-2947(99)01
912-5].