  We investigate the dynamical condensation process in a magnetized thermally
bistable medium. We perform one-dimensional two fluid numerical simulations
that describe the neutral and ionized components in the interstellar medium
with purely transverse magnetic fields. We find that the clouds that are formed
as a consequence of the thermal instability always have a magnetic field
strength on the order of a few microgauss irrespective of the initial strength.
This shows good agreement with the measurements of the magnetic field strength
in diffuse clouds. We show analytically that the final magnetic field strength
in the clouds is determined by the balance between ambipolar diffusion and the
accumulation of the magnetic field due to condensation.
