1. J. G. Daunt and E. Lerner, eds., Monolayer and Submonolayer Helium Films (Plenum Press, New York, 1973).
2. J. G. Dash, Films on Solid Surfaces (Academic Press, New York, 1975).
3. P. Monod and J. A. Cowen, preprint (unpublished).
4. H. T. Weaver, J. Phys. Chem. Sol. 34, 421 (1973).
5. D. F. Brewer, D. J. Creswell, Y. Goto et at., in Ref. 1, p. 101.