Evolution of the radial velocity perturbation u′ during the first three orbital periods of the N-body simulation with n = 25 and q = 0.4 of Fig. 13. Clearly visible is the periodic variation of the radial size of the simulation region according to Eq. (68) which is drawn as dashed curves. Also indicated is the analogous radial variation of one wavelength of the seeded mode, represented by the two pairs of red solid curves. Since the seed is a standing wave, its amplitude undergoes an oscillation with twice the overstable wave frequency (cf. Eq. (15)).