We now turn to consideration of those instabilities characteristic of inhomogeneous plasmas. As we remarked earlier, additional sources of free energy associated with the spatial variations of physical quantities are available in these circumstances. A nonuniform system, therefore, has a natural tendency to release this extra amount of free energy and thereby to approach a uniform state of thermodynamic equilibrium. The magnetic field applied to the plasma usually places certain constraints on the motion of charged particles; ordinary relaxation processes through collisions may not provide a sufficiently effective mechanism by which such an equilibrium may be approached. The onset of an instability may then have to be looked upon as an alternative avenue through which the plasma finds it preferable to release the extra free energy; so-called anomalous relaxations would thereby result in the plasma.