1. Booker, J. R. & Bretherton, F. P. 1967 J. Fluid Mech. 27,513.
2. Oster, G. 1965 Sci. American,212, no. 2,p.70.
3. Jones, Walter L. 1967 J. Fluid Mech. 30,439.
4. Bretherton, F. P. 1966 Quart. J. Roy. Met. Soc. 92,394.
5. Hughes, T. H. & Reid, W. H. 1967 To appear in Phil. Trans.