\begin{table}%t7
\caption{ Electron density indicators in NGC~3242.\label{tab7}}
%\centerline
 {\begin{tabular}{lcccc}
\hline
\hline
Ion &Ioniz. & Lines& Observed &$N_{{\rm e}}$ \\
&Pot. (eV) & used  & ratio & (cm$^{-3}$)\\
\hline
\ion{[S}{ii]} & 10.4 & 6731/6716 & 1.38  & 1900\\
\ion{[O}{ii]} & 13.6 & 3626/3729 & 1.61 & 2700 \\
\ion{[S}{iii]} & 23.3 & 33.5/18.7 & 0.38: & 2800 \\
\ion{[Cl}{iii]} & 23.8 & 5538/5518 & 1.08 & 3000\\
\ion{C}{iii]} & 24.4 & 1906/1909 & 1.29 & 3300:\\
\ion{[O}{iii]} & 35.1 & 51.8/88.4 & 2.24 & 900:\\
\ion{[Ar}{iv]} & 40.7 & 4711/4740 & 1.08 & 2100:\\ 
\ion{[Ne}{iv]} & 63.5 & 2425/2422 & 0.92 & 5000: \\
\hline
\end{tabular}}
\par
\smallskip
: Indicates uncertain values.\\ Wavelengths of the far infrared lines are in
microns, the rest are in Angstroms.
\end{table}