418 



The Application of the Microscope to the Investigation of Me- 

 teorites.— The difficulties in the way of the complete investiga- 

 tion 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 imper- 

 fectly crystallized. Moreover the methods for separating 

 them, whether mechanically or chemically, are very incom- 

 plete. With a view to obtain some more satisfactory means 

 of dealing Avith these aggregates 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 metorite itself; and one finds that it is not difficult roughly 

 to classify nieteorities according to the varieties of their 

 structure. In this way one recognises constantly recurring 

 minerals ; but the method aff"ords 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 

 crystallographic 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 Avith the problem was by employ- 

 ing the microscope chiefly as a means of selecting and 

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

 the various minerals that compose it, and then investigating 

 each se2:)arately by means of the goniometer and by analysis, 

 and finally recurring to the microscopic sections to identify 

 and recognise the minerals so investigated. 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 

 amoitnts of a meteorite can be spared for the purpose, not- 

 withstanding 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 desira- 

 bility 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, Avhich was adopted. — 

 Professor Maskelyne in the ' Proceedings of the Royal 

 Society, 1870.' 



