  We argue that existing measurements of ep collisions at HERA --in which an
energetic photon is made via a QED `Compton' subprocess-- can provide rather
detailed information on the photonic parton density of the proton. This
function and its deviations from Bjorken scaling should be measurable, allowing
for an interesting test of the theory. The photonic distribution function and
its gluonic counterpart should show a strikingly different evolution with
momentum scale.
