On the theories of form optical rotation —The existence of two zeroes in the rotatory dispersion curve

The rotatory dispersion has been measured for a mixture of optically active l-menthol and n-p-methoxybenzylidene-p′- butylaniline (MBBA) which simulates a cholesteric liquid crystal in its behaviour. The rotatory dispersion exhibits two zeroes in contradiction to the theoretical results for form optical rotation based on Oseen's dielectric continuum model. However, the existence of these zeroes is in agreement with the theory based on difference equations for wave propagation in a periodic structure.