\begin{table}%t2 
%\centering
\par
\caption{\label{tab2}Observation of M17 (Fig.~\ref{fig1}).}
\vspace*{-2mm}
%%%   -----------------------------    table 2
%
\par
\begin{tabular}{rrccccccccc} 
\hline
\hline
\noalign{\smallskip}
 $n$ &\multicolumn{2}{c}{Wavelength} 
& \multicolumn{2}{c}{$F$($\lambda$)/$F$(H$\beta$)} 
&\multicolumn{2}{c} {$F$($\lambda$)/$F$(H$\beta$)} 
&\multicolumn{2}{c} {$F$($\lambda$)/$F$(H$\beta$)} 
&\multicolumn{2}{c} {$F$($\lambda$)/$F$(H$\beta$)} \\
  &\multicolumn{2}{c}{} &\multicolumn{2}{c}{region A} 
  &\multicolumn{2}{c}{region B} & \multicolumn{2}{c}{region C}
  & \multicolumn{2}{c}{region N~3} \\
  & P & H & P & H & P & H & P & H & P & H \\
\hline
 3 & --   & 6563 &  --  &532  & --   &1102\  & --   &667  & --  & 510  \\
 4 & --   & 4861 &  --  &100  & --   &\ 100  & --   &100  & --  & 100 \\
 5 & --   & 4340 &  --  &31.8 & --   &\ 22.3 & --   &32.0 & --  & 29.78\\
 6 & 10~938& 4103 & 75.4\ &12.6& --   &\ 11.4 & --   &11.6 & --  & 11.27 \\
 7 & 10~049& 3970 & 37.3\ &6.62& 250\ &\ 6.7  & 141  &(6.5) & -- & --  \\
 8 & 9546 &*3889 & 23.0\ &7.28~(3.86)& 256\ & --  &  79.9& -- & -- & --  \\
 9 & 9229 & 3835 & 14.7\ &2.28&  82.7& --    & 51.79& -- & 12.6 & 1.51  \\
10 & 9015 & 3797 &  9.00&1.54 &  43.5& --    & 16.22& -- & 7.71 & 0.98  \\
11 & 8863 & 3770 & 7.57~(6.29)&1.37~(1.12) &  33.3& -- & -- & -- & -- & -- \\
12 & 8750 & 3750 & 5.86~(4.47)&0.94 &  29.6& --  & --  & --  & -- & --     \\
\hline
%    &F(H$\beta$) &     &  50.67  &  3.56  &  1.50     &     58.97 \\
%\hline
\end{tabular}
\vspace*{-1.5mm}
\tablefoot{$^*$ Blend with HeI 3889~\AA. 
Values in bracket: corrected to obtain a smooth decrement (Fig.~\ref{fig2}).}
 \end{table}