  In this paper we analyse a set of 33 optical spectra, which were acquired
with the ARCES echelle spectrograph (R = 38,000) on the 3.5-m telescope at the
Apache Point Observatory. We examine the H{\alpha} profile in each of these
observations in order to determine the geometry and velocity structure of the
previously discovered bipolar jet, which originates from the secondary star of
HD 44179 located at the centre of the Red Rectangle nebula. Using a 3D
geometric model we are able to determine the orbital coverage during which the
jet occults the primary star. During the occultation, part of the H{\alpha}
line profile appears in absorption. The velocity structure of the jet was
determined by modelling the absorption line profile using the Sobolev
approximation for each orbital phase during which we have observations. The
results indicate the presence of a wide angle jet, likely responsible for
observed biconical structure of the outer nebula. Furthermore, we were able to
determine a likely velocity structure and rule out several others. We find that
the jet is comprised of low-density, high-velocity, central region and a
higher-density, lower-velocity, conical shell.
