xcvi GENERAL SUMMARY OF SCIENTIFIC AND 



mide, and iodide of silver arc sensitive to rays of both high 

 and low refrangibility, this sensitiveness also depends on the 

 bodies which may be mixed with them, those colored bodies 

 which absorb certain colors (and which promote photograph- 

 ic reduction) increasing the sensibility of the silver salt for 

 the absorbed rays. Moreover, certain colorless bodies which 

 promote photographic reduction, and certain others which 

 influence the index of refraction, also modify the color-sensi- 



bilitv. 



MINERALOGY. 



The mineralogists in this country and abroad have been 

 far from inactive during the past year, as, in fact, is well 

 shown in the long list of new minerals which is appended. 

 Their investigations have covered a considerable part of the 

 known mineral species, and have resulted in adding much to 

 what has already been published about them. 



One of the most important of these memoirs is that by 

 Des Cloizeaux on the optical properties of the feldspar 

 family. He is a profound authority on such subjects, so 

 that these investigations, including a ready means for dis- 

 tinguishing the different feldspar species, become of very- 

 great value. The same author has given a crystallographic 

 and optical description of the rare species durangite, which 

 was named some years since by Professor Brush. Another 

 important French contribution to the science is a memoir 

 by Daubree on the recent formation of a number of minerals 

 in the thermal waters at Bourbonne-les-Bains ; these include 

 tetrahedrite, bornite, anglesite, etc. These observations are 

 important as bearing upon the paragenesis of minerals in 

 general. 



The number of doubtful minerals has been diminished by 

 the chemical and microscopical studies of Mr. G. W. llawes, 

 who has shown that neither chlorastrolite nor zonochlorite 

 deserve places as distinct species. A similar service has 

 been performed by Professor Klein, who by a series of crys- 

 tallographic investigations has shown that the supposed wis- 

 erine of Kenngott is nothing but a peculiar form of octahe- 

 drite. Mr. llawes has also put the very doubtful mineral of 

 Liebe, diabantachronnyn, on a proper footing. The mineral 

 in question is important as occurring frequently in some ig- 

 neous rocks, and is now called diabantite. Professor Cooke 



