Has not seen the paper in the Smithsonian Institution, but believes the author is in error. Has looked at A. L. Cauchy's Dispersion Memoir, but thinks Baden Powell's paper presents a more distinct formula. Hopes to send in a few weeks the first volume of HL's [Observations Made at the Magnetic and Meteorological Observatory at Trinity College, Dublin].

Comments that A. J. Fresnel's papers in the Annales de chimie are really incomplete sketches of theories, which he developed later. Theory clearly stated in [Felix] Billet's Traité d'optique physique. Friend of his at Trinity College has produced a peculiar liquid.