Reversed Pleochroic Haloes

IN a paper on “The Genesis of Pleochroic Haloes” (Phil. Trans. R.S., vol. ccxvii.) by J. Joly, a theory is advanced accounting for certain structural features of the halo on the assumption that, reversal of the. halo-image is possible, and may take place under conditions defined in the paper. In support of this a drawing of a halo is given in which an evident inversion or change from positive to negative has occurred, the inner region being light, the outer dark.