A new design of tiltmeter has been used to measure the tidal bending of the Ronne Ice Shelf, Antarctica. By this means the point at which the ice sheet leaves the land and starts floating on the sea has been defined to within 600m. Monitoring this position in future should give an indication of the state of balance of the West Antarctic ice sheet, often considered1 to be unstable even if not actually disintegrating. The hydrostatic level meter is light and simple and can operate unattended while recording continuously for periods of several weeks. Observations at eight different sites on Rutford Ice Stream (Fig. 1) gave tidal records on ice more than 1,700 m thick and at points up to 600 km from the nearest open sea.