Series of H$_\alpha$ spectra and slit-jaw H$_\alpha$ filtergrams of a quiescent prominence (QP) taken at Pic du Midi Observatory on 7 November 1977 are studied. The image processing of the H$_\alpha$ filtergrams reveals an internal structure of the prominence consisting of several arches. Series of high-resolution H$_\alpha$ spectra obtained with the slit located on selected parts of one of the prominence arches chosen for Doppler shift analysis. The prominence arch show cyclic displacement along the line-of-sight (L.O.S.) direction implying Alfven string-mode oscillations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html