14f) Proceedings of Philosophical Societies. [Feb. 



Secretary. — Dr. Hope. 



Counsellors of the Physical Class. — Lord Webb Seymour, Mr. 

 Leslie, Colonel Irnrie, Mr. Jameson, Dr. Brewster, and Mr. 

 James Jardine. 



President of the Literary Class. — Henry Mackenzie, Esq. 



Secretary. — Thomas Thomson, Esq. 



Counsellors of the Literary Class. — Mr. Pillans, Dr. Mack^ 

 night, Mr. Dunbar, the Rev. Mr. Alison, Lord Reston, and Rev.. 

 Dr. Jamieson. 



Dec. 1. — A paper, by Dr. Brewster, was read on the Laws of 

 Double Refraction and Polarisation. 



This paper was divided into seven sections, of which only the 

 two first were read. 



I. On the crystals which produce double refraction, a property 

 which the author has observed in 160 crystals. 



II. On crystals with one apparent axis of double refraction. 

 These crystals, which amount to twenty-two, were divided into 

 two classes, positive and negative, and include all those whose 

 primitive form is the hexahedral prism, the rhomboid with an 

 obtuse summit, and the octohedron, in which the pyramids have 

 a square base. 



III. On crystals with two axes of double refraction and pola- 

 risation. These crystals, which amount to about eighty, include 

 all those whose primitive form is not the hexahedral prism, the 

 obtuse rhomboid, the octohedron with a square base, the cube, 

 the regular octohedron, and the rhomboidal octohedron. 



IV. On the resolution and combination of polarising forces, 

 and the reduction of all crystals to crystals with two or more 

 axes. 



V. On crystals with three equal and rectangular axes. These 

 crystals amount to twenty, and consist of those whose primitive 

 form is the cube, the regular octohedron, and the rhomboidal 

 dodecahedron. 



VI. On the artificial imitation of all the classes of doubly 

 refracting crystals. 



VII. On the laws of double refraction, for crystals with any 

 number of axes. 



Dec. 15. — »A paper was read which had been announced at 

 the first meeting, by Dr. Murray, containing Experiments on 

 Muriatic Acid. He had repeated the experiment performed by 

 Dr. Ure, of subliming muriate of ammonia over ignited metals, 

 with the variation of operating on the salt formed by the combi- 

 nation of muriatic acid and ammoniacal gases, instead of the 

 common sal-ammoniac which, from its mode of preparation, 

 might be supposed to contain water. He obtained a similar 

 result, water appearing when the muriate of ammonia was sub- 

 limed over iron at a red heat in a glass tube. His attention hav- 

 ing been thus recalled to the subject, he repeated the experiment 

 which he had performed some year* ago, of obtaining water from 



