\begin{table}
\caption{\label{equiv}Scalar-matrix analogies.}
\small%\centering
\par
\begin{tabular}{ll}
\hline\hline
 Scalar	&Matrix
 \\\hline 
  Complex gain		&Jones matrix
\\Visibility		&Coherency matrix
\\Brightness		&Stokes $I$ and $\pp$ brightnesses
\\Sky image		&Quartet of images, one for each of\\
& the 4 Stokes parameters 
  \\\hline 
 % \vspace{-18mm} 
  \end{tabular}
  \end{table}