The photo-elastic dispersion of vitreous silica

Abstract

1. The dispersion of the double refraction induced by stress in isotropic transparent substances has been the subject of a number of investigations. All of these, however, have dealt with compound substances, such as ordinary glasses and nitro-cellulose. It appeared of interest to obtain data, as accurate as possible, for a substance of glassy type, containing only a single chemical constituent, and in which the complications arising from progessive creep (such as occurs in nitro-cellulose and gelatine) were absent. Vitreous silica provides such a material and is now obtainable in fair-sized blocks of good optical quality. 2. Two rectangular blocks of vitreous silica were obtained from the Thermal Syndicate, Ltd. Their dimensions were as follows: a (the height) being parallel to the line of stress, b (the height) being at right angles to both the line of stress and the rays of light, and d (the thickness) being in the direction of travel of the light through the block:- A. a = 2.142, b = 0.467, d = 0.902. B. a = 4.270, b = 1.228, d = 3.250.