  Galaxy cluster mass distributions are useful probes of Omega_0 and the nature
of the dark matter. Large clusters will distort the observed shapes of
background galaxies through gravitational lensing allowing the measurement of
the cluster mass distributions. For most cases, the agreement between weak
lensing and radial velocity mass measurements of clusters is reasonably good.
There is, however, one significant exception, the z=0.32 cluster MS1224.7+2007,
which has a lensing mass substantially larger than the virial mass and also a
very high mass-to-light ratio. Since this controversial object might be an
unusually dark mass a follow-up study is definitely warranted. In this paper we
study the mass and light distributions of MS1224+2007 out to a projected radius
of 800/h kpc by measuring the gravitationally-induced distortions of background
galaxies. We detect a shear signal in the background galaxies in the radial
range 27.5 arcsec < r < 275 arcsec at the 5.5 sigma level. The resultant mass
map exhibits a peak centered on the dominant cluster galaxy and strong evidence
for substructure which is even more strongly seen in the galaxy distribution.
Assuming all the detected shear is due to mass at z=0.32 we find cluster
mass-to-light ratio of M/L_R = 640 +/- 150. The mass profile is quite flat
compared to other clusters, disagreeing with a pseudo-singular isothermal
sphere at the 95% confidence level. Our mass and M/L estimates are consistent
with the previous weak lensing result. The discrepancy between the lensing and
virial mass remains although it might be partially explained by subclustering
and infall perpendicular to the line-of-site. This cluster remains a candidate
dark object deficient in baryons and as such severely tests cosmological
models.
