Further researches into the properties of the sulphate of lodo-quinine or Herapathite, more especially in regard to its crystallography, with additional facts concerning its optical relations

Joseph Beete Jukes, Esq., was admitted into the Society. The reading of Dr. Herapath’s paper was resumed and concluded. After referring to the observations of Professors Stokes and Haidinger, as well as to papers already published by himself on this subject in the Philosophical Magazine, the author gives an account of a set of prisms perfectly complementary in their optical characters to those previously described by him, and proves this fact by an elaborate comparison of their various optical relations; from which it appeared, that whilst theα -prisms (those described in Philosophical Magazine for March 1852) were totally impervious to a beam of polarized light, reflected from glass plates, when the plane of the length of the prism was at right angles to the plane of primitive polarization, theβ -prisms (those now examined) were equally absorbent of a vertically polarized beam, when the plane of their length lay parallel to that of primitive polarization.