146 



Mr. N. Story-Maskelyne on the 



[Jan. 13, 



I. " On the Mineral Constituents of Meteorites." By Nevil 

 Story-Maskelyxe, M.A., Professor of Mineralogy in the Uni- 

 versity of Oxford, and Keeper of • the Mineral Department, 

 British Museum. Communicated by Prof. H. J. Stephen 

 Smith. Received October 9, 1869. 



(Abstract.) 



I. The Application of the Microscope to the Investigation of Meteorites. 



The difficulties in the way of the complete investigation of a meteorite 

 resemble those we meet with in terrestrial rocks. In both the ingredient 

 minerals are minute, and are often, especially in the case of the aerolitic 

 rock, very imperfectly crystallized. Moreover the methods for separating 

 them, whether mechanically or chemically, are very incomplete. With a 

 view to obtain some more satisfactory means of dealing with these aggre- 

 gates of mixed and minute minerals, I sought the aid of the microscope, by 

 having in the first place sections of small fragments cut from the meteorites 

 so as to be transparent. 



One may learn, by a study and comparison of such sections, something 

 concerning the changes that a meteorite has passed through ; for one soon 

 discovers that it has had a history, of which some of the facts are written in 

 legible characters on the meteorite itself ; and one finds that it is not 

 difficult roughly to classify meteorites according to the varieties of their 

 structure. In this way one recognizes constantly recurring minerals ; but 

 the method affords no means of determining what they are. Even the 

 employment of polarized light, so invaluable where a crystal is examined by 

 it of which the crvstallographic orientation is at all known, fails, except in 

 rare cases, to be a certain guide to even the system to which such minute 

 crystals belong. It was found that the only satisfactory way of dealing with 

 the problem was by employing the microscope chiefly as a means of select- 

 ing and assorting out of the bruised debris of a part of the meteorite the 

 various minerals that compose it, and then investigating each separately by 

 means of the goniometer and by analysis, and finally recurring to the 

 microscopic sections to identify and recognize the minerals so investi- 

 gated. The present memoir deals with the former part of this inquiry. 

 Obviously the amount of each mineral thus determined, after great care 

 and search, can only be extremely small, as only very small amounts of a 

 meteorite can be spared for the purpose, notwithstanding that as large a 

 surface as possible of its material requires to be searched over for instances 

 of any one of the minerals occurring in a less than usually incomplete form. 

 On this account one has to operate with the greatest caution in performing 

 the analysis of such minerals ; and the desirability of determining the 

 silica with more precision than is usually the case in operations on such 

 minute quantities of a silicate suggested to me the process, which, after 

 several experiments in perfecting it, assumed the following form. 



