  From recent high resolution observations obtained with the Swedish 1 m Solar
Telescope in La Palma, we detect swaying motions of individual filament threads
in the plane of the sky. The oscillatory character of these motions are
comparable with oscillatory Doppler signals obtained from corresponding
filament threads. Simultaneous recordings of motions in the line of sight and
in the plane of the sky give information about the orientation of the
oscillatory plane. These oscillations are interpreted in the context of the
magnetohydrodynamic theory. Kink magnetohydrodynamic waves supported by the
thread body are proposed as an explanation of the observed thread oscillations.
On the basis of this interpretation and by means of seismological arguments, we
give an estimation of the thread Alfv\'en speed and magnetic field strength by
means of seismological arguments.
