tokens: from the spine. Previously published high-resolution images show that filaments consist of numerous very fine threads. On the other hand, panel (a), which is a cutout from the full-disk image, has the spatial resolution about 1′′–2′′. Therefore, the barbs seen here are understood to be groups of smaller threads below the spatial resolution. The directions of the polarization signals in panel (b) coincide with the H α spine and barb structure very well. The direction somewhat varies from part to part of the filament, but it is approximately parallel to the H α spine or barbs in any part. This result confirms previous deductions that the structure in filaments is confined to follow the magnetic field. Plasma motions in filaments have been observed to be along the fine threads (Lin et al. 2003 , 2005 , 2008 ), and also verify the field-aligned nature of the threads of filaments. Because the polarization directions of the filament in Figure 2 (b) are roughly aligned with either the spine or barbs, the average polarization direction for all of the filament structure without differentiating between the spine and barbs can be defined; it is shown by a dashed line in the inset at the lower-right of panel (b). The green line shows the direction of the axis of the filament, which represents the average direction of the polarity inversion line seen in panel (b), which is approximately along a straight line. In the case of the filament in Figure 2 , these two lines intersect at an angle of 180. In this case, the average polarization direction deviates from the filament axis by −180. The deviation angle is defined as an acute angle and a positive value corresponds to the counterclockwise deviation; in this case, the deviation is clockwise. This deviation angle is considered to be the deviation angle of the magnetic field vector with respect to the polarity inversion line. As mentioned in Section 1 , it is known that H α structures in filaments shows a chiral nature (see e.g., Zirker et al. 1997 ; Martin 1998 ). As in the case of the filament shown in Figure 2 , where the filament has barbs along the sides of the filament that bend downward to the right and make acute angles to the right side of the filament axis, the chirality is “right-bearing” (dextral). The alternative chirality is “left-bearing” (sinistral). The spine/barbs structure and the deviation by an acute angle of the average polarization direction with respect to the axis of the filament are schematically illustrated at the bottom of Figure 2 . It is known that right(left)-bearing filaments are dominant in the northern (southern) hemisphere, and actually the filament is located in the northern hemisphere as shown in Figure 1 . The magnetic field direction shown in Figure 2 (b) has the 180° ambiguity, and it cannot be solved only with our polarization measurements. However, Martin et al. ( 1994 ) revealed that the direction of the magnetic field can be interpreted as shown in the
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