\begin{table}%t1
%%\centering
\par
\caption{Water vapour seeing at three astronomical sites. The Fried parameter $r_0$ is given at
500~nm, adapted from the values of \citet{Racine05}. References for the {\it PWV} data are given in the
last column. The standard deviation of water vapour seeing at Dome~C is deduced from the data at
Cerro Paranal and Mauna Kea following Eq.~(\ref{eq:pwv}). Water vapour seeing was measured on a
baseline of 66~m (resp.\ 100~m) at Paranal (resp.\ Mauna Kea), and we assume that our estimate at
Dome~C is valid for a similar range of baseline lengths.\label{tab:pwv}} 
\begin{tabular}[h]{ccccc} 
\hline\hline
         Site     &  $r_0$  & $\langle {\it PWV}
\rangle$ & $\sigma_{\it PWV}$ & References
\\ \hline Cerro Paranal & 14.5~cm & 3~mm       & 27~$\mu$m  & \citet{Meisner02}
\\        Mauna Kea     & 17.8~cm & 1.6~mm     & 11~$\mu$m  & \citet{Colavita04}
\\        Dome C        & 38.2~cm & 0.25~mm    & 1~$\mu$m & \citet{Bussmann05}
\\ \hline
\end{tabular}
\end{table}