[en] The ratio of real to imaginary parts of the forward scattering amplitude (rho) is a quantity of fundamental interest which should, if possible, be measured through Coulomb-nuclear interference in an early experiment at ISABELLE. If small angle proton-proton elastic scattering is spin independent, then the optical theorem, crossing symmetry, and the basic tenets of quantum field theory allow rho to be written as a dispersion integral of sigma/sub T/(s) over s. The test of such dispersion relations at increasingly higher energies serves to confirm the validity of these assumptions over increasingly smaller distances. A report is given of an effort to determine if such a measurement can be made in the first round of experiments at ISABELLE