  We present imaging polarimetry of the extremely luminous, redshift 2.3 IRAS
source FSC10214+4724. The observations were obtained with HST's Faint Object
Camera in the F437M filter, which is free of strong emission lines. The 0.7
arcsec long arc is unresolved to 0.04 arcsec FWHM in the transverse direction,
and has an integrated polarization of 28 +/- 3 percent, in good agreement with
ground-based observations. The polarization position angle varies along the arc
by up to 35 deg. The overall position angle is 62 +/- 3 deg east of north. No
counterimage is detected to B = 27.5 mag ($3\sigma$), giving an observed arc to
counterimage flux ratio greater than 250, considerably greater than the flux
ratio of 100 measured previously in the I-band. This implies that the
configuration of the object in the source plane at the B-band is different from
that at I-band, and/or that the lensing galaxy is dusty.
