  In this letter we present calibrated mass and light profiles of the rich
cluster of galaxies Abell 1689 out to 1 $h^{-1}$ Mpc from the center. The high
surface density of faint blue galaxies at high redshift, selected by their low
surface brightness, are unique tools for mapping the projected mass
distribution of foreground mass concentrations. The systematic gravitational
lens distortions of $10^4$ of these background galaxies in 15\arcmin\ fields
reveal detailed mass profiles for intervening clusters of galaxies, and are a
direct measure of the growth of mass inhomogeneity. The mass is measured
directly, avoiding uncertainties encountered in velocity or X-ray derived mass
estimates.
  Mass in the rich cluster Abell 1689 follows smoothed light, outside 100
h$^{-1}$ kpc, with a rest-frame V band mass-to-light ratio of $400 \pm 60$
$h^{-1} (M/L_V)_\odot$. Near the cluster center, mass appears to be more
smoothly distributed than light. Out to a radius of 1 $h^{-1}$ Mpc the total
mass follows a steeper than isothermal profile. Comparing with preliminary high
resolution N-body clustering simulations for various cosmogonies on these
scales, these data are incompatible with hot dark matter, a poor fit to most
mixed dark matter models, and favor open or $\Lambda > 0$ cold dark matter.
Substructure is seen in both the mass and the light, but detailed
correspondence is erased on scales less than 100 $h^{-1}$ kpc.
