  In a sample of 7.8 million $J/\psi$ decays collected in the Beijing
Spectrometer, the process J/$\psi\to\gamma\eta_c$ is observed for five
different $\eta_c$ decay channels: $K^+K^-\pi^+\pi^-$, $\pi^+\pi^-\pi^+\pi^-$,
$K^\pm K^0_S \pi^\mp$ (with $K^0_S\to\pi^+\pi^-$), $\phi\phi$ (with $\phi\to
K^+K^-$) and $K^+K^-\pi^0$. From these signals, we determine the mass of
$\eta_c$ to be $2976.6\pm2.9\pm1.3$ MeV. Combining this result with a
previously reported result from a similar study using $\psi(2S)\to\gamma\eta_c$
detected in the same spectrometer gives $m_{\eta_c} = 2976.3\pm2.3\pm1.2$ MeV.
For the combined samples, we obtain $\Gamma_{\eta_c} = 11.0\pm 8.1\pm 4.1$ MeV.
