SUMMARY1. The unstirred layer of fluid bounding the posterior surface of the rabbit cornea and contact lens has been directly measured using an optical apparatus.2. Small polystyrene latex spheres (< 0-25 ,c diameter) were used as an indicator because of the excellent light-reflective properties; other indicators were used (e.g. carmine particles) and had a similar behaviour.3. With the bulk solution unstirred the layer was 350 ,u thick on the cornea and 150 ,c thick on the contact lens. Following vigorous stirring the layer was reduced to 65 ,u on the cornea and < 20 ,u on the contact lens.4. The present direct measurements of the unstirred layer thickness confirm previous indirect measurements.

The relationship between microstructure and physical behavior is especially pronounced in synthetic multilayer materials. Insight to the mechanisms responsible for changes in the mechanical properties can be investigated through a careful examination of the multilayer microstructure. A dominant feature of the nultilayer structure is the interface. The population of interlayer boundaries, that is interfaces, is directly proportional to the multilayer period for any given film thickness. In this paper, we will evaluate “TEM” images of multilayer systems. The interface structure will be viewed in cross-section and a range of layer thicknesses will be considered. Variation in the elastic modulus, yield stress, and microhardness have been observed for noble-transition metal systems over a wide range of multilayer periods, from less than 1 nm to greater than 1000 nm. In epitaxial systems, the extent of superlattice perfection (coherency effects) is closely tied with changes in physical behavior. Emphasis will thus be placed on the str'ucture and strain distribution from the interface, and its role in determining the mechanical properties of multilayers.