  The modification to four--dimensional Einstein gravity at low energy in two
brane models is investigated within supergravity in singular spaces. Using
perturbation theory around a static BPS background, we study the effective
four--dimensional gravitational theory, a scalar--tensor theory, and derive the
Brans--Dicke parameter when matter is present on the positive tension brane
only. We show there is an attractor mechanism towards general relativity in the
matter dominated era. The dynamics of the interbrane distance are discussed.
Finally, when matter lives on both branes, we find that there is a violation of
the equivalence principle whose magnitude is governed by the warping of the
extra dimension.
