  We observe vacuum Rabi splitting in a lossy nearly confocal cavity indicating
the strong coupling regime, despite a weak single-atom single-mode coupling.
Strong collective interaction manifests itself in the typical
$\sqrt{N}$-dependence of the normal mode splitting on the number of atoms $N$.
The $TEM_{00}$-mode coupling parameters are
$(g,\kappa,\gamma)=2\pi\times(0.12,0.8,2.6)$ MHz and up to $(1.33\pm
0.08)\times10^5$ cesium atoms were loaded into the mode volume.
