text: For a Maclaurin spheroid of eccentricity greater than 0.812670, a Jacobi ellipsoid of the same angular momentum has lower total energy.  If such a spheroid is composed of a viscous fluid (or in the presence of gravitational radiation reaction), and if it suffers a perturbation which breaks its rotational symmetry, then it will gradually elongate into the Jacobi ellipsoidal form, while dissipating its excess energy as heat (or gravitational waves).  This is termed secular instability; see Roberts–Stewartson instability and Chandrasekhar–Friedman–Schutz instability.  However, for a similar spheroid composed of an inviscid fluid (or in the absence of radiation reaction), the perturbation will merely result in an undamped oscillation.  This is described as dynamic (or ordinary) stability.
  A Maclaurin spheroid of eccentricity greater than 0.952887 is dynamically unstable.  Even if it is composed of an inviscid fluid and has no means of losing energy, a suitable perturbation will grow (at least initially) exponentially.  Dynamic instability implies secular instability (and secular stability implies dynamic stability).