  We present optical spectroscopy of the microquasar SS433 covering a
significant fraction of a precessional cycle of its jet axis. The components of
the prominent stationary H-alpha and H-beta lines are mainly identified as
arising from three emitting regions: (i) a super-Eddington accretion disc wind,
in the form of a broad component accounting for most of the mass loss from the
system, (ii) a circumbinary disc of material that we presume is being excreted
through the binary's L2 point, and (iii) the accretion disc itself as two
remarkably persistent components. The accretion disc components move with a
Keplerian velocity of ~600 km/s in the outer region of the disc. A direct
result of this decomposition is the determination of the accretion disc size,
whose outer radius attains ~8 R_sun in the case of Keplerian orbits around a
black hole mass of 10 M_sun. We determine an upper limit for the accretion disc
inner to outer radius ratio in SS433, R_in/R_out ~ 0.2, independent of the mass
of the compact object. The Balmer decrements, H-alpha/H-beta, are extracted
from the appropriate stationary emission lines for each component of the
system. The physical parameters of the gaseous components are derived. The
circumbinary ring decrement seems to be quite constant throughout precessional
phase, implying a constant electron density of log N_e(cm^-3) ~ 11.5 for the
circumbinary disc. The accretion disc wind shows a larger change in its
decrements exhibiting a clear dependence on precessional phase, implying a
sinusoid variation in its electron density log N_e(cm^-3) along our
line-of-sight between 10 and 13. This dependence of density on direction
suggests that the accretion disc wind is polloidal in nature.
