Annu. Rev. Astron. Astrophys. 1996. 34: 155-206
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2.4. Comparison with Optical Polarization Data

Optical polarization observations have revealed spiral magnetic patterns in M51 (Scarrott et al 1987), NGC 1068 (Scarrott et al 1991), NGC 1808 (Scarrott et al 1993), and other galaxies (Scarrott et al 1990) (see also the review by Hough 1996). In the western half of M51, field orientations as derived from optical polarization disagree by up to about 60° from the spiral pattern as derived at several wavelengths in the radio continuum Beak et al 1987. Optical polarization is contaminated by highly polarized light due to scattering at large angles. Polarization observations at far-infrared or submillimeter wavelengths are free from scattering effects and reveal the magnetic field structure in Galactic dust clouds (Davidson et al 1995) and near the Galactic Center (Hildebrand et al 1990, Hildebrand & Davidson 1994).