FROM FEYNMAN HISTORIES TO OBSERVABLES

We analyze a quantum observable f given by the time average of a dynam ical variable F along a Feynman path. We show that f can be described by a (generalized) wave function satisfying the Schrodinger-like equat ion and measured by a meter similar to that of von Neumann. A connecti on with operators is established. Examples include the particle's mome ntum, energy and the fractional traversal time. [S1050-2947(98)50503-3 ].