Royal Society. 221 



sideration that a particle situated in the common surface of the two 

 media cannot vibrate in more than one way at once. Of these three 

 equations two involve the amplitudes of the first component wave, 

 and the third those of the second. The five equations serve to de- 

 termine, in terms of the angle of incidence and the component am- 

 plitudes of the incident wave, the five following quantities, namely, 

 the angle of refraction, the two component amplitudes of the re- 

 flected wave, and those of the refracted wave. 



By the aid of the result referred to, that every loss of vis viva is 

 always accompanied by a diminution of the refractive index, coupled 

 with the general view which he takes of the cause of absorption, 

 the author is enabled to give an explanation of Frauenhofer's lines, 

 and in general of the lines of absorption in coloured media ; and also 

 to explain the phenomena discovered by Sir David Brewster, that 

 violet light may exist in the blue spaces, and blue light in the red. 



In the course of the investigation, the altered expressions for the 

 intensities of the reflected and refracted rays, so far as they are 

 affected by the coefficient of absorption, are given. The expressions 

 for the intensities of the two component reflected waves are very 

 little affected j but those for the intensities of the two component 

 refracted waves are materially altered in value. 



The theory likewise affords an explanation, the first the author 

 believes that has ever been offered, of the remarkable properties of 

 saccharine solutions and of certain crystals, such as right-handed 

 and left-handed quartz, which exhibit the phenomenon of circular 

 polarization. 



June 16. — The following papers were read : — 



1. "On the Anatomy and Physiology of Cordylophora, a contri- 

 bution to our knowledge of the Tubularian Zoophytes." By George 

 James Allman, M.D., M.R.I.A., Professor of Botany in the Univer- 

 sity of Dublin, &c. 



The author, after pointing out the necessity of giving greater de- 

 finiteness to the terminology employed in the description of the true 

 zoophytes, proceeds to the anatomical details of Cordylophora, a genus 

 of Tubulariad<£. He demonstrates that Cordylophora is essentially 

 composed in all its parts of two distinct membranes enclosing a 

 cavity, a structure which is common to all the Hydroida. For 

 greater precision in description, he finds it necessary to give to these 

 membranes special names, and he therefore employs for the external 

 the name of ectoderm, and for the internal that of endoderm. Each of 

 these membranes retains its primitive cellular structure. In the ecto- 

 derm thread-cells are produced in great abundance ; these are formed 

 in the interior of the ectodermal cells by a process of endogenous cell- 

 formation, and are afterwards set free by the rupture of the mother- 

 cell. The thread-cells in a quiescent state are minute ovoid capsules, 

 but under the influence of irritation, an internal sac is protruded by 

 a process of evagination ; the surface of the evaginated sac is 

 furnished with a circle of curved spicula, and from its free extremity 

 a delicate and long filament is emitted. The thread-cells of Cordy- 

 lophora thus closely resemble the " hastigerous organs " of Hydra. 



