  We introduce the concept of effective geometry by studying several systems in
which it arises naturally. As an example of the power and conciseness of the
method, it is shown that a flowing dielectric medium with a linear response to
an external electric field can be used to generate an analog geometry that has
many of the formal properties of a \Sch black hole for light rays, in spite of
birefringence. The surface gravity of this analog black hole has a contribution
that depends only on the dielectric properties of the fluid (in addition to the
usual term dependent on the acceleration). This term may be give a hint to a
new mechanism to increase the temperature of Hawking radiation.
