In this paper we present a detailed analysis of a number of quiescent
prominences for which the components of the magnetic field as well as
the electron density and emission measure were previously obtained fro
m quasi-simultaneous measurements in hydrogen Her and helium D-3 lines
. From magnetic equilibrium models of the Kippenhahn-Schluter type one
can calculate the gas pressure, density, column mass and geometrical
width. The same set of physical parameters can also be derived from a
NLTE hydrogen-line analysis. We have studied the mutual correlations b
etween these two sets of parameters. Very large differences, reaching
an order of magnitude, were found between these two sets, both for ind
ividual prominences and for the mean values over all prominences used
in this investigation. Finally, we discuss some implications of our re
sults.