a Compound of Iodine and Codeine. 125 



diate brightness, and that perpendicular to the intersection 

 of the two planes AA and BB the darkest. All have, how- 

 ever, the same fundamental dark orange-colour, and are 

 distinguished only by differences of intensity. 



The adamantine surface-lustre, when, examined by reflec- 

 tion with the dichroscopic lens, is decomposed in such a 

 manner, that a portion of the reflected light is definitely 

 polarized {fast polarisirt) in 

 the direction of the edge dd', ^ *^' 



or as E in fig. 1. In the po- 

 sition represented in fig. 3, all 

 the ordinary polarized light 

 passes into the upper image, 

 the extraordinary polarized 

 into the lower image, and the 



contrast is then most complete. In the position perpendi- 

 cular to this, all the definitely polarized light, along with the 

 white surface lustre, passes into the upper image. In the 

 position represented in fig. 3, the colour is not equally blue 

 at all angles of incidence. When the angle becomes con- 

 siderable, the colour passes into violet, and when it becomes 

 very high, an imperfect bronze yellow makes its appearance 

 in the lower, contrasted with a bright white in the upper, 

 image. 



The crystals now described afford a new confirmation of 

 the law already laid down by me in the second part of the 

 " Sitzungsberichte," viz., that the determinate surface-lustre, 

 or the definitely polarized surface colour, corresponds in the 

 direction of its polarization with that of the more absorbed 

 ray of doubly refracting crystals.* 



According to Dr Anderson, the chemical constitution of 

 this substance is not yet fully determined, and in default of a 

 systematic name, I propose to designate these crystals, so in- 



* As there is some diflSculty in translating this law so as exactly to express 

 Professor Haidinger's meaning, we give it here in the original, in which it 

 stands thus : — " Der orientirte Flachenschiller, oder die fest polarisirte Oher- 

 flachenfarhe in der Polarisationsrichtung mit der Polarisationsrichtung der 

 mehr absorbirten Strahles doppelt brechender Krystalle iibereinstimmt." 



