  The CNOC1 cluster survey measures Omega_M via Oort's method, Omega_M= M/L x
j/rho_c, where M/L is the field mass-to-light ratio, j is the field luminosity
density and rho_c is the closure density. A wide range of potential systematic
effects are explicitly controlled by independently deriving the mean cluster
mass profile (finding good agreement with theoretical predictions), the cluster
light profile, the redshift evolution of both cluster and field galaxies, the
differential evolution between the two, and the field and cluster efficiencies
for the conversion of baryons into galaxies. We conclude that
Omega_M=0.19+/-0.06 where the errors are objectively evaluated via resampling
methods. The redshift evolution of the numbers of clusters per unit co-moving
volume over the 0< z < 0.6 range is found to be very slow, as is required for
consistency with a low density universe. The evolution of galaxy clustering in
the field is compatible with a low density universe, and strongly disfavors
models of galaxy evolution that associate low density halos with individual
galaxies.
