1864.] Mr. ^oxhy on the Microscopical Structure of Meteorites, 333 



2. That the primary maximum occurred at the quadratures in 1845 and 

 1846, and one day earlier in 1844. 



3. That the primary minimum occurred at the syzygies in 1844 and 

 1845, and one day later in 1846. 



4. That 1846 was a disturbed year ; and if it were omitted from the Table, 

 each of the remaining years, as well as the average, would exhibit an entire 

 correspondence with theory, except in the primary maximum of 1844. 



5. That 1845 was a normal year, the primary and secondary maxima 

 and minima all corresponding with theory, both in position and relative value. 



XII. " On the Microscopical Structure of Meteorites.^^ 

 By H. C. SoRBY, r.H.S., &c. Received June 7, 1864. 



For some time past I have endeavoured to apply to the study of meteo- 

 rites the principles I have made use of in the investigation of terrestrial 

 rocks, as described in my various papers, and especially in that on the 

 microscopical structure of crystals (Quart. Journ. Geol. Soc. 1858, vol. xiv. 

 p. 453). I therein showed that the presence in crystals of ''fluid-, glass-, 

 stone-, or gas-cavities" enables us to determine in a very satisfactory manner 

 under what conditions the crystals were formed. There are also other 

 methods of inquiry still requiring much investigation, and a number of 

 experiments must be made which will occupy much time ; yet, not wishing 

 to postpone the publication of certain facts, I purpose now to give a short 

 account of them, to be extended and completed on a subsequent occasion*. 



In the first place it is important to remark that the divine of meteorites 

 contains most excellent "glass-cavities," similar to those in the olivine of 

 lavas, thus proving that the material was at one time in a state of igneous 

 fusion. The olivine also contains " gas-cavities," like those so common in 

 volcanic minerals, thus indicating the presence of some gas or vapour 

 (Aussun, Parnallee). To see these cavities distinctly, a carefully prepared 

 thin section and a magnifying power of several hundreds are required. 

 The vitreous substance found in the cavities is also met with outside and 

 amongst the crystals, in such a manner as to show that it is the uncrystal- 

 line residue of the material in which they were formed (Mezo-Madaras, 

 Parnallee). It is of a claret or brownish colour, and possesses the charac- 

 teristic structure and optical properties of artificial glasses. Some isolated 

 portions of meteorites have also a structure very similar to that of stony 

 lavas, where the shape and mutual relations of the crystals to each other 

 prove that they were formed in situ, on solidification. Possibly some entire 

 meteorites should be considered to possess this peculiarity (Stannern, New 

 Concord), but the evidence is by no means conclusive, and what crystalli- 

 zation has taken place in situ may have been a secondary result ; whilst in 

 others the constituent particles have all the characters of broken fragments 



* The names given thus (Stannern) indicate what meteorites I more particularly refey 

 to in proof of the variouo facts previously stated. 



