  This paper is a review of a previous research on gravitational waves from the
R^-1 high order theory of gravity. It is shown that a massive scalar mode of
gravitational waves from the R^-1 theory generates a longitudinal force in
addition of the transverse one which is proper of the massless gravitational
waves and the response of an arm of an interferometer to this longitudinal
effect in the frame of a local observer is computed. Important conseguences
from a theoretical point of view could arise from this approach, because it
opens to the possibility of using the signals seen from interferometers to
understand which is the correct theory of gravitation.
