VII. On the dispersion in artificial double refraction

Abstract

It is well known that glass and other transparent isotropic substances, when compressed unequally in different directions, behave like doubly-refracting substances and exhibit the colours of polarized light. Attention was first called to this by Fresnel (‘Annales de Chimie et de Physique,' vol. XX.), and by Sir David Brewster (‘Phil. Trans.,' 1816). For further investigations in this field, reference may be made to F. E. Neumann (‘Abhandlungen der k. Acad. v. Wissenschaften zu Berlin,' 1841, II.; see also ‘Pogg. Ann.,' vol. LIV.); to Clerk Maxwell (‘Trans, Roy. Soc. Edin.,’ vol. XX., Part I.; or ‘Collected Papers,' vol. I.); to G.Wertiieim (‘Annales de Chimie et de Physique,' ser. 3, vol. XL., p. 156); to J. Kerr (‘Phil. Mag.,' October, 1888); and to F. Pockels (“Über die Änderung des optischen Yerhaltens verschiedener Glaser durch elastische Deformation,” ‘Ann. d. Physik,' 1902, ser. IV., vol. VII., p. 745). Of these only Wertheim and Pockels have considered how the effect varies with the nature of the light employed. If homogeneous parallel light is passed perpendicularly through a plate of thickness τ which is subjected to principal stresses P, Q in its plane, these stresses being uniform throughout, then it is found that the light on traversing the plate is broken up into two rays polarized in the directions of principal stress. The relative retardation in centimetres of these rays on emergence is given by R = ( μ 1 - μ 2 ) τ , where μ 1 , μ 2 are the indices of refraction of the two rays.