  We report quantitative experimental results for the intensity of
noise-induced fluctuations below the critical temperature difference $\Delta
T_c$ for Rayleigh-B\'enard convection. The structure factor of the fluctuating
convection rolls is consistent with the expected rotational invariance of the
system. In agreement with predictions based on stochastic hydrodynamic
equations, the fluctuation intensity is found to be proportional to
$1/\sqrt{-\epsilon}$ where $\epsilon \equiv \Delta T / \Delta T_c -1$. The
noise power necessary to explain the measurements agrees with the prediction
for thermal noise. (WAC95-1)
