348 J . T. Stuart and others considered to move in the instability diagram of equivalent wavenumber against Reynolds number, in the sense th a t these param eters are time-and space-dependent for the evolution of the disturbance-wave system. For our detailed calculations we use a quadratic approximation to the eigenrelation, an approxim ation which is quite accurate. If the initial distribution implies a point within the neutral curve, when the plates are squeezed together the equivalent

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... ber falls while the equivalent Reynolds number rises, and amplification takes place until the lower branch of the neutral curve is nearly crossed. If the plates are pulled apart (dilatation) the equivalent wavenumber rises, while the Reynolds number drops, and amplification takes place until the upper branch of the neutral curve has been just crossed. In the case of dilatation the transition from amplification to damping takes place more quickly than for the case of squeezing, in p art due to the geometry of the neutral curve.