1. Auer, L. H., Fabiani Bendicho, P. and Trujillo Bueno, J. (1994), A&A, 292, 599
2. Auer, L. H. and Paletou, F. (1994), A&A, 285, 675
3. Cannon, C. J. (1970) ApJ, 161, 255
4. Carlsson, M. and Stein, R.F. (1997), ApJ, 481, 500
5. Dittmann, O.J.: 1999, in K.N. Nagendra, J.O. Stenflo (eds.), Solar Polarization, Proc. 2nd SPW, Kluwer, Dordrecht, (in this Volume)