Abstract
For decades, the determination of the mean density of matter (ΩM) has been tied to the distribution of light. This has led to a "bias," perhaps as large as a factor of 2, in determining a key cosmological parameter. Recent measurements of the physical properties of clusters, the cosmic microwave background anisotropy, and the power spectrum of mass inhomogeneity now allow a determination of ΩM without "visual bias." The early data lead to a consistent picture of the matter and baryon densities, with ΩB = 0.039 ± 0.0075 and ΩM = 0.33 ± 0.035, respectively.