1883.] 343 [Annual Meeting. 



Comparative Mineralogy is divided into three topics. 

 1st. Composition and chemical relations of Minerals. 

 2nd. Form and structure of Minerals ; crystallography. 

 3rd. Physical properties of Minerals. 



The first and second topics are fully dealt with in one of the 

 floor cases, the pyramidal end of which is occupied by the ele- 

 ments, and the third in another of the same size, which stands 

 parallel with it. 



In this general account we can, of course, only allude to a few 

 series which may be used as examples of the mode of arrangement. 

 We have, however, added a fuller account in an appendix, since 

 we have reason to believe that this mode of arrangement is in 

 some respects unique in its design and execution. 



The following are some of the examples of the mode of treat- 

 ment of the sub-topics of the 1st, 2nd, and 3rd subdivisions of 

 comparative mineralogy marked by the letters of the alphabet 

 to distinguish them from the grouping indicated by the Arabic 

 numerals. 



(a). Variations due to chemical substitution are shown by a 

 series of seven minerals among which are three principal varieties 

 ofAmphibole, and three of Garnet exhibiting the variations in 

 color, and aspect due to changes in the composition of the varie- 

 ties. 



(b). Variations due to alteration and decomposition of minerals 

 by a series of five minerals, among which are Orthoclase and 

 Wernerite, two distinct minerals undergoing change to the same 

 mineral, Kaolinite, by decomposition. 



(c). Only one substance is devoted to the exposition of the 

 great differencies which may exist between the constituents of a 

 mineral and the compound resulting from their union ; Pyrrho- 

 tite and its elements, sulphur and iron, are placed together upon 

 one tablet. 



d). Adiffi3ULt s:ibJ3ct to dial with in an exhibition of this 

 kind which is wholly addressed to the eye is magnetism, this is 

 shown by arranging a series as follows: — 



