  The data of ground-based telescopes of Global Oscillation Network Group
(GONG) obtained in the H-alpha line provide an opportunity to study the
long-period oscillations of chromospheric filaments (quiescent prominence). For
the first time, on the base of time-series of 5 days duration, combined from
the observations of three observatories of the GONG, a new ultra-low mode, with
period between 20 and 30 hours, was reliably detected in oscillations of a
long-lived dark filament on the solar disc.
