The Photo-elastic Properties of Glass
JSGT_1929_V13_T213_T219

 
It is a well-known fact that glass and other transparent bodies under stress acquire the property of double refraction. Sir David Brewster who first observed this stated that for a plate of glass stressed transversely to the direction of propagation of the light, the axes of polarisation in the glass are along and perpendicular to the direction of stress. Also he stated that glass under pressure behaves like a negative uniaxial crystal, and under tension like a positive uniaxial crystal, the optic axes in each case being along the line of stress.

F. C. Harris