\begin{table}%t1  
 \caption{\label{tab1}Dust cross-section $\sigma$ at 250~\micron\ as a function of radius in M~33, expressed in units of $1.1 \times 10^{-25}$~cm$^2$ per H-atom.}   
%\centerline
{\small
\begin{tabular}{lrrrrrr}   
\hline \hline  
$r$ (kpc) & 4 & 5& 5.5 &6& 7& 7.5 \\
\hline
Polygons & 1.8 & 1.02 &..& 1.07 & 0.66 & 0.50  \\
histo-$N$   & 0.65 &..& 0.54 & ..& ..&0.48 \\
histo-$S$   & 0.92 &..& 0.95 & 0.69&.. &.. \\
% radius & $<5$ & $<6$ & $<7$ & $<7.5$ \\
Model   & 0.8 &..& 0.75 &..& 0.66 & 0.5 \\
\hline
\end{tabular}}
\tablefoot{The polygons are shown in Fig.~\ref{fig3}.  The histogram method was applied separately in the north and south (lines~2 and~3), leading to the ``Model'' values used to estimate the total H column density to make Fig.~\ref{fig4}.}\vspace*{-3.5mm}  
\end{table}