  We report a study of $\bar p+p\to \bar p+X+Y$ at $\sqrt s=1800$ GeV, where
$Y$ is a proton or system of mass-squared $M_Y^2\lesssim 8$ GeV$^2$. In a
sample of events with a leading $\bar p$ of fractional momentum loss
$0.035<\xi_{\bar p}<0.095$ and 4-momentum transfer squared $|t_{\bar p}|<1.0$
GeV$^2$, the proton fractional momentum loss $\xi_p^X$ to the system $X$ was
evaluated from the momenta of the particles comprising $X$. In the region
$\xi_p^X<0.02$, the $\xi_p^X$ distribution behaves as $\sim 1/(\xi_p^X)^{1.1}$,
as expected for double Pomeron exchange. The fraction of events with
$\xi_p^X<0.02$ is found to be $0.194\pm 0.001 {\rm (stat)}\pm 0.012 {\rm
(syst)}$.
