  Several processes of meson production in proton-deuteron collisions have been
measured simultaneously using a calibrated magnetic spectrograph. Among these
processes, the $\eta$ meson is seen clearly as a sharp missing--mass peak on a
slowly varying background in the $p+d\to ^3\textrm{He} +X$ reaction. Knowing
the kinematics of the other reactions with well determined masses, it is
possible to deduce a precise mass for the $\eta$ meson. The final result,
$m(\eta)=547.311\pm 0.028 \textrm{(stat)} \pm 0.032 \textrm{(syst) MeV/c}^2$,
is significantly lower than that found by the recent NA48 measurement, though
it is consistent with values obtained in earlier counter experiments.
