a passive marker including a tuned circuit having an inductance and a capacitance carried by a carrier enclosed within a hollow sphere that is partially filled with a liquid to freely float the carrier . the inductance includes a coil which , when the carrier is floating , positions the axis of the coil so it is closer to the vertical than the horizontal . the passive marker is of a type that is buried relative to portions of utilities such as gas , telephone , water and power lines , for use in locating such portions when necessary .