2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36070String theory suggests the existence of gravitational-strength scalar fields (``dilaton'' and ``moduli'') whose couplings to matter violate the equivalence principle. This provides a new motivation for high-precision clock experiments, as well as a generic theoretical framework for analyzing their significance.9 pages, Latex, to appear in the Proceedings of the Workshop on the Scientific Applications of Clocks in Space (JPL, Pasadena, November 7-8, 1996)General Relativity and Quantum Cosmologytext