8 Prof. Forbes on the Optical Characters of Greenockite. 



generally received. In the present case, for example, our 

 green compound would be represented 



By C 30 H 40 -f I 2 according to Berzelius. 



By C 60 H 40 -J- I 2 according to Dumas. 

 And by C so H 20 + I according to British chemists. 

 The compounds of carbon and hydrogen therefore, on the 

 principle of Berzelius, which abstractedly is very valuable as 

 a guide for general nomenclature, would receive in the works 

 of different chemists at least two, and sometimes three differ- 

 ent names of foreign origin. Trivial names therefore derived 

 as heretofore from different and various sources, will be likely 

 in the present state of the science to create much less con- 

 fusion in our rapidly extending, already exceedingly difficult 

 and almost Protean nomenclature. 

 Durham, May 16, 1840. 



II. On the Optical Characters of Greenockite {Sulphur el of 

 Cadmium). By James D. Forbes, Esq., F.R.SS. L. and 

 Ed., Professor of Natural Philosophy in the University of 

 Edinburgh.* 



FT appears from a late number of Professor Jameson's 

 •*- Journal, that the crystallographic characters of this new 

 mineral, as examined by Mr. Brooke, remain ambiguous, and 

 that the crystals sent to him for examination do not enable 

 him positively to say whether it belongs to the rhombohedral 

 or to the prismatic system; it may therefore be interesting to 

 state that I have discovered that it possesses only one axis of 

 double refraction in the direction of the axis of the pyramid or 

 prism in which it usually crystallizes, and consequently there 

 can be no doubt that greenockite is a rhombohedral cadmium 

 blende. 



Edinburgh, May 18, 1840. 



III. On a new Species of Biliary Calculus. By Thomas 



Taylor, M.li.C.S. 



To the Editors of the Philosophical Magazine and Journal, 



Gentlemen, 

 Vl/'HILST engaged in examining the extensive collection 

 *" of calculi in the museum of the Royal College of Sur- 

 geons, which had been entrusted to me for that purpose by the 

 Board of Curators, I remarked, among those in the Hunterian 

 collection, one, which from its extreme lightness and peculiar 



* Communicated by the Author. We were favoured with this article in 

 the middle of May, but from an oversight which we regret its insertion 

 was omitted. 



