  We present and analyze experimental results on the dynamics of hydrothermal
waves occuring in a laterally-heated fluid layer. We argue that the large-scale
modulations of the waves are governed by a one-dimensional complex
Ginzburg-Landau equation (CGLE). We determine quantitatively all the
coefficients of this amplitude equation using the localized amplitude holes
observed in the experiment, which we show to be well described as Bekki-Nozaki
hole solutions of the CGLE.
