  Measurements of infrared conductivity in the normal state of the cuprate
layer metals show a characteristic behavior in the plane of the layers which is
in essential agreement among many experiments. A simple parametrization of this
behavior, proposed originally by Collins and Schlesinger, and exploited by N.
Bontemps and her group, which gives an adequate fit over frequencies from a few
hundred cm$^{-1}$ to $>5000 $ cm$^{-1}$, is that the phase angle of the complex
conductivity is independent of frequency. This fit is shown to be a natural
consequence of Luttinger Liquid theory with charge-spin separation, and
determines the exponent of the singularity at the Fermi surface to be $\sim
.15\pm .05$.
