  The spin excitation continuum, expected to dominate the low-energy
fluctuation spectrum in the Haldane spin chain around the Brillouin zone
center, q=0, is directly observed by inelastic magnetic neutron scattering in
the S=1 quasi-1D antiferromagnet CsNiCl3. We find that the single mode
approximation fails, and that a finite energy width appears in the dynamic
correlation function S(q,omega) for q < 0.5pi. The width increases with
decreasing q, while S(q,omega) acquires an asymmetric shape qualitatively
similar to that predicted for the 2-magnon continuum in the nonlinear
sigma-model.
