  If 7Be solar neutrinos can be observed in real time experiments, then an
extended region of Delta m^2 can be probed by a proper analysis of the rapidly
changing phase of vacuum oscillations due to the eccentricity of the earth's
orbit about the sun. For the case of maximal vacuum mixing, a kind of Fourier
analysis of expected data for one year's time could uniquely pick out Delta m^2
if it lies in the region ~10^{-10} - 6 X 10^{-9} (eV)^2.
