The Spectral Dispersion of Birefringence, Especially of Birefringent Plastic Sheets

It is shown apparently for the first time how dispersion of birefringence (retardation, phase difference or ellipticity) can be measured through the visible spectrum by the use of a Martens type of polarization photometer and monochromator. Dispersion curves are given for several organic thermoplastic sheets including those with both normal and abnormal dispersion of birefringence, and possible uses for such sheets are suggested.