a1 Mathematisches Institut der Universität Bonn, Beringstraβe 1, 5300 Bonn, Germany
In this note we study Borel-probability measures on the unit tangent bundle ofa compact negatively curved manifold M that are invariant under the geodesic flow. We interpret the entropy of such a measure as a Hausdorff dimension with respect to a natural family of distances on the ideal boundary of the universal coveringof M. This in term yields necessary and sufficient conditions for the existence of time preserving conjugacies of geodesic flows.
(Received December 18 1990)
(Revised April 19 1991)