122 Prof. Haidinger on the Optical Properties of 



On the Optical Properties of a Compound of Iodine and Codeine."^ 

 By William Haidinger, Esq., Councillor of Mines in 

 Austria, and Professor of Mineralogy, F.R.S.E., Member 

 of the Wernerian Nat. Hist. Soc. of the Royal Academies 

 of Berlin, Munich, &c., &c. Communicated by the Author. 



The crystals which I now submit to the notice of the 

 physico- mathematical section of the Academy belong to the 

 class of those which reflect the incident ray with coloured 

 polarization, while the transmitted ray presents a colour dif- 

 ferent from, and complementary to, that reflected from the 

 surface. They form an individual example of a series of 

 substances exhibiting all the modifications of the colour 

 spectrum in their transmitted, reflected, internal, and surface 

 colours, with which I have been engaged for some time past, 

 and which I hope soon to be able to submit to the Academy 

 in a connected form. These crystals, however, appear to me 

 to deserve an earlier notice, as they are the result of an 

 entirely new, and, as yet, incomplete investigation of Dr 

 Anderson of Edinburgh, by whom they have been trans- 

 mitted to me through the hands of my colleague, Professor 

 Schrotter. 



The crystals are tabular, apparently equilateral triangular 

 plates, and, at first sight, I was inclined to seek for a 

 rhombohedral form in the arrangement of the narrow faces 

 distributed on the edges. A more minute examination, how- 

 ever, proved them to belong to the Anorthoid system, and 

 their form is shewn in the accompanying figure. If we 

 assume the large face O as 

 the terminal plane or base of Fig- 1- 



the crystallographic series, 

 m and m' may be considered 

 as the left and right faces of 

 a rhomboidal prism, the limit 

 of the series of the anorthoid 

 forms, that is as / oo A/2, and 

 r 00 A/2. Of the two faces 

 I 00 A/2 only the anterior + face occurs, the posterior 



* From the *' Sitzungsberichte" of the Vienna Academy of Sciences. 



