The optical anisotropy and heterogeneity of vitreous silica

Summary

The paper describes the birefringence exhibited by vitreous silica, both in the naturally occurring material found in the Libyan desert and in the commercially available material in the forms of rods and disks. The facts revealed by the investigation are discussed. It is shown that Rayleigh’s belief that vitreous silica in the mass has a crystalline granular structure cannot be sustained. It is shown further that, besides the familiar stress-optical birefringence, a second kind of effect,viz., “structural birefringence” is also possible in amorphous solids and that this is particularly prominent in vitreous silica for reasons which are discussed.

12 photographs illustrate the paper.