Left: raster observations of SoHO/CDS (Coronal Diagnostic Spectrometer) (Harrison et al. 1995) in the Hei 584.33 Å line made on April 26, 2007 between 13:03:34 and 13:30:08 UT. The position of the SoHO/SUMER slit is marked. Right: Meudon/MSDP image of the prominence obtained in the Hα line centre at 12:47 UT overlaid with the contours of the same prominence observed from 13:03 UT with SoHO/CDS in Hei 584.3 Å line (image in the left panel). The position of SoHO/SUMER slit with respect to the Hα prominence is also marked. The numbers along the slit show the coordinates of the axis used in our work and the next figures. The length of the slit was 120″. Both images are plotted in the same spatial scale. For the analysis of the observed and theoretical prominence emission we used only the part of SoHO/SUMER spectra between 10″ and 46″.