On the Twyman effect and some of its applications

Abstract

This review is a survey of a number of papers on the Twyman effect, discovered in 1905, in the processing of optical glass. The subject of these works is a detailed study of the Twyman effect in optical glass, quartz and sapphire crystals, and metals in the form of thin wafers with a thickness of 1 to 0.1 mm. It has been established that plane-parallel wafers of the studied materials, ground on one side and polished on the other, bend until the surface becomes strictly spherical or elliptical, concave on the polished side with a radius of curvature in a quadratic dependence of the wafers' thickness and not depending on their size and shape. A phenomenological conclusion of the main law has been drawn. It reveals the physical sense of the Twyman effect through its connection with the surface tension of solids. Three new methods have been worked out which are rather interesting prospective applications of the Twyman effect (for studying anisotropy in crystals, for processing concave spherical mirrors, for measuring apparatus and for preparing a new type of spherical crystalline diffraction lattice for X-ray spectroscopy).