\begin{table}%t3
%\centering
\par
\caption{KOSMA-$\tau$ calculations of H$_2$, C and CO column 
densities of spherical clumps with $n=10^5$~\cmcub\ and $\chi =
10^2$ (Draine units). The column densities are for individual clumps, and
not the column densities observed per beam.
\label{pdrmod}}
\begin{tabular}{llllcc}
\hline\hline
\noalign{\smallskip}
%! M <NH2> <NC> <NCO> <N13CO> <N(C)>/<N(CO)> R[pc]     
$M_{\rm cl}$ & $N$(H$_2$)$_{\rm cl}$ & $N$(C)$_{\rm cl}$ & $N$(CO)$_{\rm cl}$ & $\frac{N(\rm {C^0})}{N(\rm {CO})}_{\rm cl}$ &
$R_{\rm cl}$\\
& 10$^{21}$ & 10$^{16}$ & 10$^{17}$ & &\\
\msun & cm$^{-2}$ & cm$^{-2}$& cm$^{-2}$& & pc\\
\hline
10    &  31  &  23  &  79  &  0.03  &  0.077\\
1     &  14  &  20  &  32  &  0.06  &  0.036   \\  
0.1   &  6.6 &  14  &  13 &   0.11  &  0.017    \\ 
0.01  &  3.3 &  8.7 &  4.0 &  0.22  &  0.008    \\ 
0.001 &  1.3 &  4.2 &  1.0 &  0.43  &  0.004    \\ 
\hline
\end{tabular}
\end{table}