  Several hotspots of FRII radio sources have previously been detected in the
X-ray at a flux level consistent with the X-rays being due to inverse-Compton
scattering of radio synchrotron photons (`synchrotron self-Compton'), if the
magnetic fields in the hotspots are close to their equipartition values.
However, the number of hotspots compact and bright enough to exhibit detectable
X-ray emission is small, so it is worth searching for synchrotron self-Compton
emission in the optical, in spite of the obvious observational difficulties of
such an approach. In this note I report on a possible detection of an optical
inverse-Compton hotspot in a deep Hubble Space Telescope observation of the
distant quasar 3C196, at a level which implies a hotspot magnetic field
strength close to equipartition if the electrons have a low-energy cutoff
around gamma ~ 500.
