\begin{table}%f4
%\centering
\par
\caption{\label{tab_dens}Electron densities in particles per cm$^3$ of [S{\sc ii}] and [O{\sc ii}] measured for each of the knots.}
\small
\begin{tabular}{l c c}
\hline\hline
 Knot & $n$([O{\sc ii}])  & $n$([S{\sc ii}]) \\
 \hline
A & $<$200 & $<$230 \\
B & $<$85 & $<$160 \\
C & $<$180 & $<$210 \\
D & $<$190 & $<$350 \\
\hline
\end{tabular}
\end{table}