1. Gaster, M. 1962 J. Fluid Mech. 14,222.
2. Betchov, R. & Criminale, W. O. 1966 Phys. Fluids,9, 359.
3. Gaster, M. & Davey, A. 1968 J. Fluid Mech. 32,801.
4. Mack, L. M. 1976 J. Fluid Mech. To appear.
5. Mattingly, G. E. & Criminale, W. O. 1972 J. Fluid Mech. 51,233.