  We report measurements of the temperature fluctuations in a horizontal layer
of a pure fluid confined between parallel plates and heated from below.
Consistent with earlier work we found that the structure factor $S_T(q)$ (the
square of the modulus of the Fourier transform of the temperature field) was
consistent with $S_T(q) \sim q^{-4}$ for large horizontal wavenumbers $q$. As
$q$ decreased, $S(q)$ increased less rapidly, passed through a maximum, and
then approached zero. The results agree qualitatively, but not quantitatively,
with the predictions of Ortiz de Z\'arate and Sengers.
