\begin{table}%t3
%\centering
\par
\caption{\label{tab:prevqso}Previous circular polarization measurements of quasars and BL~Lac objects.}
\par
\begin{tabular}{lcccr}
\hline\hline  \noalign{\smallskip}
Object &  $z$  &  $p_{\rm lin}$ (\%) &  $\theta_{\rm lin}$ ($\degr$) &  $p_{\rm circ}$ (\%) \\ 
\hline 
0237$-$233 & 2.223 &   0.25 $\pm$ 0.29     &   $-$\tablefootmark{d} & $-$0.06 $\pm$ 0.08\tablefootmark{a} \\
0955$+$326 & 0.533 &   0.18 $\pm$ 0.24     &   $-$\tablefootmark{c} &    0.06 $\pm$ 0.08\tablefootmark{a} \\
1127$-$145 & 1.187 &   1.30 $\pm$ 0.40     &  23 $\pm$ 10\tablefootmark{e} &    0.32 $\pm$ 0.20\tablefootmark{a} \\ 
1156$+$295 & 0.729 &   2.68 $\pm$ 0.41     & 114 $\pm$  4\tablefootmark{f} &    0.12 $\pm$ 0.14\tablefootmark{b} \\
1222$+$228 & 2.058 &   1.09 $\pm$ 0.16~[u] & 167 $\pm$  4\tablefootmark{i} &    0.23 $\pm$ 1.80\tablefootmark{i} \\
1226$+$023 & 0.158 &   0.25 $\pm$ 0.04     &  58 $\pm$  4\tablefootmark{c} & $-$0.01 $\pm$ 0.02\tablefootmark{g} \\
1253$-$055 & 0.536 &   9.00 $\pm$ 0.40     &  67 $\pm$  1\tablefootmark{e} &    0.09 $\pm$ 0.07\tablefootmark{a} \\
1308$+$326 & 0.997 &  12.10 $\pm$ 1.50     &  68 $\pm$  3\tablefootmark{e} & $-$0.08 $\pm$ 0.17\tablefootmark{b} \\
1634$+$706 & 1.334 &   0.24 $\pm$ 0.07~[u] &   4 $\pm$  8\tablefootmark{i} & $-$0.05 $\pm$ 0.09\tablefootmark{i} \\
1641$+$399 & 0.594 &   4.00 $\pm$ 0.30     & 103 $\pm$  2\tablefootmark{e} & $-$0.05 $\pm$ 0.23\tablefootmark{b} \\
2230$+$114 & 1.037 &   7.30 $\pm$ 0.30     & 118 $\pm$  1\tablefootmark{e} & $-$0.05 $\pm$ 0.17\tablefootmark{a} \\
2302$+$029 & 1.044 &   0.66 $\pm$ 0.12~[u] & 136 $\pm$  5\tablefootmark{i} & $-$0.39 $\pm$ 0.16\tablefootmark{i} \\
{\it 0138$-$097} & 0.733 &  3.60 $\pm$ 1.50 & 168 $\pm$ 11\tablefootmark{e} & 0.25 $\pm$ 0.35\tablefootmark{k} \\
{\it 0219$+$428} & 0.444 & 26.11 $\pm$ 0.19 &   3 $\pm$  1\tablefootmark{k} & 0.16 $\pm$ 0.05\tablefootmark{k} \\
{\it 0422$+$004} & 0.310 & 10.29 $\pm$ 0.23 & 179 $\pm$  1\tablefootmark{g} &    0.14 $\pm$ 0.07\tablefootmark{g} \\
{\it 0735$+$178} & 0.424 & 11.69 $\pm$ 0.22 & 123 $\pm$  1\tablefootmark{k} & 0.03 $\pm$ 0.05\tablefootmark{k} \\
{\it 0823$-$223} & 0.910 & 14.39 $\pm$ 0.16 &  11 $\pm$  1\tablefootmark{k} & 0.16 $\pm$ 0.08\tablefootmark{k} \\
{\it 0851$+$202} & 0.306 & 10.80 $\pm$ 0.30 & 156 $\pm$  1\tablefootmark{e} & $-$0.01 $\pm$ 0.02\tablefootmark{a} \\
{\it 1101$+$384} & 0.031 &  2.59 $\pm$ 0.11 &  10 $\pm$  1\tablefootmark{h} & 0.02 $\pm$ 0.03\tablefootmark{h} \\
{\it 2155$-$304} & 0.116 &  4.12 $\pm$ 0.25 &  93 $\pm$  2\tablefootmark{j} & $-$0.02 $\pm$ 0.02\tablefootmark{j} \\
{\it 2200$+$420} & 0.068 &  4.90 $\pm$ 0.40 & 147 $\pm$  2\tablefootmark{e} & $-$0.07 $\pm$ 0.19\tablefootmark{a} \\
\hline 
\end{tabular}
\tablefoot{All but a few polarization measurements were
obtained in white light; the multi-color measurements in references
($h$), ($j$) and ($k$) were averaged; [u] refers to linear and circular
polarization measurements averaged over the 2200--3200~\AA\
ultraviolet wavelength band; the circular polarization of objects
2200$+$420 and 2230$+$114 was obtained in the 4000--6000~\AA\ and
3500--5200~\AA\ bands respectively; italicized names indicate objects
classified as BL~Lac in V\'eron-Cetty \& V\'eron
(\cite{VER06}). References for linear and circular polarization:
\tablefoottext{a}{Landstreet \& Angel (\cite{LAN72});} 
\tablefoottext{b}{Moore \& Stockman
(\cite{MOO81});} 
\tablefoottext{c}{Stockman et~al. (\cite{STO84});} 
\tablefoottext{d}{Moore \& Stockman
(\cite{MOO84});} 
\tablefoottext{e}{Impey \& Tapia (\cite{IMP90});} 
\tablefoottext{f}{Wills et~al. (\cite{WIL92});} 
\tablefoottext{g}{Valtaoja et~al. (\cite{VAL93});} 
\tablefoottext{h}{Takalo \&
Sillanp\"a\"a (\cite{TAK93});} 
\tablefoottext{i}{Impey et~al. (\cite{IMP95});} 
\tablefoottext{j}{Tommasi
et~al. (\cite{TOM01a});} 
\tablefoottext{k}{Tommasi et~al. (\cite{TOM01b}).  }}
\end{table}