Is the magnetic field in quiescent prominences force-free?

Aims. We describe under which conditions the magnetic fields of quiescent prominences are force-free and under which gravity plays the dominant role. Methods. The existing observational determinations of the magnetic field are summarised and the calculation of the plasma beta is outlined. We derive the dependence of beta on the prominence weight and the field strength. Results. We show that in many cases of well-developed quiescent prominences the field can deviate substantially from the force-free situation and gravity fully determines the structure of the magnetic dips.