  We present 0.4 arcsec-resolution imaging polarimetry at 8.7, 10.3, and 12.5
microns, obtained with CanariCam at the Gran Telescopio Canarias, of the
central region of W51 IRS2. The polarization, as high as 14 percent, arises
from silicate particles aligned by the interstellar magnetic field. We
separate, or unfold, the polarization of each sightline into emission and
absorption components, from which we infer the morphologies of the
corresponding projected magnetic fields that thread the emitting and
foreground-absorbing regions. We conclude that the projected magnetic field in
the foreground material is part of the larger-scale ambient field. The
morphology of the projected magnetic field in the mid-IR emitting region
spanning the cometary HII region W51 IRS2W is similar to that in the absorbing
region. Elsewhere, the two magnetic fields differ significantly with no clear
relationship between them. The magnetic field across the W51 IRS2W cometary
core appears to be an integral part of a champagne outflow of gas originating
in the core and dominating the energetics there. The bipolar outflow, W51north
jet, that appears to originate at or near SMA1/N1 coincides almost exactly with
a clearly demarcated north-south swath of lower polarization. While
speculative, comparison of mid-IR and submm polarimetry on two different scales
may support a picture in which SMA1/N1 plays a major role in the magnetic field
structure across W51 IRS2.
