The Hanle Effect in Atomic and Molecular Lines: A New Look at the Sun's   Hidden Magnetism
  This paper reviews some of the most recent advances in the application of the Hanle effect to solar physics, and how these developments are allowing us to explore the magnetism of the photospheric regions that look ``empty'' in solar magnetograms--that is, the Sun's ``hidden'' magnetism. In particular, we show how a joint analysis of the Hanle effect in atomic and molecular lines indicates that there is a vast amount of hidden magnetic energy and unsigned magnetic flux localized in the (intergranular) downflowing regions of the quiet solar photosphere, carried mainly by tangled fields at sub-resolution scales with strengths between the equipartition field values and 1 kG. 
J. Trujillo Bueno, A. Asensio Ramos and N. Shchukina