\begin{table}%T3
\caption{Electron temperature indicators in \ngc.}\label{tab-3}
%\centerline
{
\begin{tabular}{lcccc}
\hline
\hline
Ion & Ioniz. & Lines& Observed & $T_{{\rm e}}$\\
 & pot. (eV)& used &ratio  & (K) \\
\hline
\ion{[N}{ii]} & 14.5 & 5755/6584 & 0.0209 & 10~000\\
\ion{[S}{iii]} & 23.3 & 6312/18.7 & 0.081 & 10~000 \\
\ion{[N}{iii]} & 29.6 & 1750/57.3 & 1.5 & 10~800\\
\ion{[O}{iii]} & 35.1 & 4363/5007 & 0.0115 & 13~000\\
\ion{[O}{iii]} & 35.1 & 1663/5007  & 0.0227 & 12~500\\
\ion{[Ne}{iii]} & 41.0 & 3868/15.5 & 0.86 & 12~500\\
\ion{[O}{iv]}  & 54.9 & 1400/25.9  & 0.126 & 15~000\\
\ion{[Ne}{iv]} & 63.4 & 2424/4725 & 95.: & 16~000\\
\ion{[Ne}{v]} & 97.1 & 3425/24.3 & 0.64.:  & 14~000\\
\ion{[Ne}{v]} & 97.1 & 3425/14.3 & 0.55.:  & 16~600\\
\ion{[Mg}{v]} & 109.3 & 2784/5.61 & 0.573 & 16~000\\
\hline
\end{tabular}}
\par
\medskip
The ":'' indicate uncertain observations.
\end{table}