Abstract: There is disclosed a photoelastic strain gauge which displays visual patterns representative of the strain in the workpiece to which the gauge is bonded. The gauge comprises two sheets of reflective material and a body of photoelastic material therebetween. A reflector in the body directs polarized light in such a way as to be reverberated between the reflective sheets and then discharged to produce the visual patterns. Because the light is reverberated, the visual patterns are amplified or enlarged.