  We describe a new actuation technique for gravity experiments based on a
liquid field mass. The Characterizing idea is to modulate the gravity force
acting on a test mass by controlling the level of a liquid in a suitable
container. This allows to obtain a periodical gravity force without moving
parts (except the liquid level) close to the TM. We describe in detail the most
relevant aspects of the liquid actuator and discuss how it can be used in
gravity experiments. In particular we analyse an application to test the
inverse square law in the mm to cm distance region.
