  We report on the generation, subsequent oscillation and interaction of a pair
of matter wave dark solitons. These are created by releasing a Bose-Einstein
condensate from a double well potential into a harmonic trap in the crossover
regime between one dimension (1D) and three dimensions (3D). The oscillation of
the solitons is observed and the frequency is in quantitative agreement with
simulations using the Gross-Pitaevskii equation. An effective particle picture
is developed and reveals that the deviation of the observed frequencies from
the asymptotic prediction $\nu_{z}/\sqrt{2}$, where $\nu_{z}$ is the
longitudinal trapping frequency, results from the dimensionality of the system
and the interaction between the solitons.
