Histogram of the α angle between the magnetic field vector and the long axis of the filament. The angle is oriented as in Fig. 4 of Leroy et al. (1984). Positive α angles correspond to normal polarity. Negative α angles correspond to inverse polarity. In the northern hemisphere, the filament is dextral when α lies inside the interval [ − 90° , + 90° ], and sinistral outside (and the reverse for the southern hemisphere). The overlined values in the top left corner are the average values, global and for each hemisphere. The associated standard deviations are also provided.