  We present an image of the redshift 2.3 IRAS source FSC10214+4724 at 0.8
microns obtained with the HST WFPC2 Planetary Camera. The source appears as an
unresolved (< 0.06") arc 0.7" long, with significant substructure along its
length. The arc is centered near an elliptical galaxy 1.18" to the north. An
unresolved component 100 times fainter than the arc is clearly detected on the
opposite side of this galaxy. The most straightforward interpretation is that
FSC 10214+4724 is gravitationally lensed by the foreground elliptical galaxy,
with the faint component a counterimage of the IRAS source. The brightness of
the arc in the HST image is then magnified by ~100 and the intrinsic source
diameter is ~0.01" (80 pc) at 0.25 microns rest wavelength. The bolometric
luminosity is probably amplified by a smaller factor (~30), yielding an
intrinsic luminosity ~2E13 solar luminosities. A detailed lensing model is
presented which reproduces the observed morphology and relative flux of the arc
and counterimage, and correctly predicts the position angle of the lensing
galaxy. The model also predicts reasonable values for the velocity dispersion,
mass, and mass-to-light ratio of the lensing galaxy. A redshift for the lensing
galaxy of ~0.9 is consistent with the measured surface brightness profile from
the image, as well as with the galaxy's SED.
