  A systematic study of the linear thermal instability of a self-gravitating
magnetic molecular cloud is carried out for the case when the unperturbed
background is subject to local expansion or contraction. We consider the
ambipolar diffusion, or ion-neutral friction on the perturbed states. In this
way, we obtain a non-dimensional characteristic equation that reduces to the
prior characteristic equation in the non-gravitating stationary background. By
parametric manipulation of this characteristic equation, we conclude that there
are, not only oblate condensation forming solutions, but also prolate solutions
according to local expansion or contraction of the background. We obtain the
conditions for existence of the Field lengths that thermal instability in the
molecular clouds can occur. If these conditions establish, small-scale
condensations in the form of spherical, oblate, or prolate may be produced via
thermal instability.
