Exhibit 169 is a press for deforming glass to demonstrate birefringence. Figure 3 illustrates the experimental setup using a polarizer, analyzer and a light source. When the polarizer is normal to the analyzer and the glass is not deformed, no light is visible on the screen. When the glass is deformed, it becomes birefringent and bands of color are visible on the screen. The space between the bands is inversely proportional to the pressure, the greater the pressure and thus the deformation, the narrower the bands.
BIBLIOGRAPHY
[1] E. Perucca,"Fisica Generale e Sperimentale", Vol. II, Torino 1963, Pag. 290
