  We present theoretical calculations and experimental measurements which
reveal finite-size effects in the tunneling between two parallel quantum wires,
fabricated at the cleaved edge of a GaAs/AlGaAs bilayer heterostructure.
Observed oscillations in the differential conductance, as a function of bias
voltage and applied magnetic field, provide direct information on the shape of
the confining potential. Superimposed modulations indicate the existence of two
distinct excitation velocities, as expected from spin-charge separation.
