13.7 Glass fragments found on a suspect’s shoes or clothes are often used to connect the suspect to a crime scene. The index of refraction of the fragments are compared to the refractive index of the glass from the crime scene. To make this comparison rigorous, we need to know the variability the index of refraction is over a pane of glass. Bennet et al. (2002) analyzed the refractive index in a pane of float glass, searching for any spatial pattern. Here are samples of the