  Gravitationally coupled scalar fields, originally introduced by Jordan, Brans
and Dicke to account for a non constant gravitational coupling, are a
prediction of many non-Einsteinian theories of gravity not excluding
perturbative formulations of String Theory. In this paper, we compute the cross
sections for scattering and absorption of scalar and tensor gravitational waves
by a resonant-mass detector in the framework of the Jordan-Brans-Dicke theory.
The results are then specialized to the case of a detector of spherical shape
and shown to reproduce those obtained in General Relativity in a certain limit.
Eventually we discuss the potential detectability of scalar waves emitted in a
spherically symmetric gravitational collapse.
