He-D3 Polarization observed in Prominences

Spectro-polarimetric measurements of the D3-HeI 5876 A line profile in 35 prominences have been performed in 2003 with the Gregory-Coud\'e Telescope in Locarno. Two different experimental techniques (ZIMPOL and Beam-exchange method) have been successfully employed to determine all four Stokes components. Both give compatible results. The preliminary results as well as the measurement techniques are reported