Page:Scientific Papers of Josiah Willard Gibbs - Volume 2.djvu/238

222 While the writer has aimed at a greater degree of rigor than is usual in the establishment of the fundamental equation of monochromatic light, it is not claimed that this equation is absolutely exact The contrary is evident from the fact that the equation does not embrace the phenomena which characterize such circularly polarizing bodies as quartz. This, however, only implies the neglect of extremely small quantities—very small, for example, as compared with those which determine the dispersion of colors. In one of the papers already cited, the case of a perfectly transparent body is treated with a higher degree of approximation, so as to embrace the phenomena in question.