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A cleavage technique has been used to measure solid/fluid interfacial energies, and to study directly the effect of various media on these energies. Solid/vapour and solid/liquid interfacial energies were measured by cleaving mica specimens first in an atmosphere of vapour and then in the corresponding liquid. In this way we have a direct means of checking the validity of Young’s equation. Results obtained with water, as representative of a polar medium, and hexane, as representative of a non-polar medium show that Young’s equation holds for systems with zero contact angle. The effect of the humidity of the surrounding atmosphere on the cleavage of mica was also investigated. Water vapour was found to produce a marked reduction in the cleavage energy. In another set of experiments the cleavage technique was used to determine the work done in separating mica surfaces covered with an adsorbed monomolecular layer of fatty acid. The results yield a value of 37 erg/cm 2 for the surface energy of a lauric acid monolayer on mica.

The influence of a variety of media on solid/fluid interfacial energies has been measured by a cleavage technique. The solid used was mica, chosen because of its near perfect cleavage and ideal bulk properties. Solid/vapour and solid/liquid interfacial energies, ysv and y s ~, were measured by cleaving specimens in the form of strips, first, in an atmosphere of the vapour and then with the specimens completely immersed in the corresponding liquid. Samples of mica coated with monomolecular films of fatty acids were constructed in such a way that separation took place between the oppositely oriented films. Polar and non-polar liquids and vapours were used in these experiments. The results allow an investigation into the validity of Young's equation for contact angles which are zero or positive. For well-behaved systems in which no adsorption takes place during the cleavage, the relation is valid. For fatty acid films in an aqueous environment, it is necessary to introduce an additiona1 term into the relation to preserve the equality, thus

The authors have used matrix methods to calculate the electrode potentials required to maintain a given conjugate focus condition for two five-element electrostatic cylinder lenses of slightly different proportions. They show that there is a simple parametrisation which allows one to calculate the focusing potentials given the overall voltage ratio and the magnification required. By using an extension of a straightforward method for calculating the potential within two closely spaced coaxial cylinders they have determined the matrix elements for a two-cylinder lens for voltage ratios from 0.01 to 100 in 200 equal logarithmic steps. These small steps simplify accurate interpolation especially for ratios close to unity.