  We report on measurements performed on an apparatus aimed to study the
Casimir force in the cylinder-plane configuration. The electrostatic
calibrations evidence anomalous behaviors in the dependence of the
electrostatic force and the minimizing potential upon distance. We discuss
analogies and differences of these anomalies with respect to those already
observed in the sphere-plane configuration. At the smallest explored distances
we observe frequency shifts of non-Coulombian nature preventing the measurement
of the Casimir force in the same range. We also report on measurement performed
in the parallel plane configuration, showing that the dependence on distance of
the minimizing potential, if present at all, is milder than in the sphere-plane
or cylinder-plane geometries. General considerations on the interplay between
the distance-dependent minimizing potential and the precision of Casimir force
measurements in the range relevant to detect the thermal corrections for all
geometries are finally reported.
