The fine structure of prominences. IV

High spatial resolution spectral observations of five hedgerow prominences were made in Hα, He I D3 and Ca II H and K. The observed relations between the lines were not the same in all prominences. The Ca II H and K lines were 2-4 times brighter relative to Hα and D3 than predicted theoretically. The optical thickness of Hα was less than for the H and K lines, the Hα was optically thin in medium faint prominence structures. Faint structures appeared slightly hotter than bright structures. (Auth.)