  We explore the dark matter distribution in ms1224.7+2007 using the
gravitational distortion of the images of faint background galaxies. Projected
mass image reconstruction reveals a highly significant concentration coincident
with the X-ray and optical location. The concentration is seen repeatably in
reconstructions from independent subsamples and the azimuthally averaged
tangential shear pattern is also clearly seen in the data. The projected mass
within a $2.76'$ radius aperture is $\simeq 3.5 \times 10^{14} h^{-1}
M_{\sun}$. This is $\simeq 3$ times larger than that predicted if mass traces
light with $M/L = 275 h$ as derived from virial analysis. It is very hard to
attribute the discrepancy to a statistical fluctuation, and a further
indication of a significant difference between the mass and the light comes
from a second mass concentration which is again seen in independent subsamples
but which is not seen at all in the cluster light. We find a mass per galaxy
visible to $I = 22$ of $\simeq 8 \times 10^{12}h^{-1}M_{\sun}$ which, if
representative of the universe, implies a density parameter $\Omega \sim 2$. We
find a null detection of any net shear from large-scale structure with a
precision of 0.9\% per component. This is much smaller than the possible
detection in a recent comparable study, and the precision here is comparable to
to the minimum level of rms shear fluctuations implied by observed large-scale
structure.
