5o6 



NATURE 



{Oct, 7, 1875 



splendid result of solar physics to establish the nature of the 

 gaseous molecules of so many elements that have as yet defied 

 the experimental methods of our terrestrial laboratories. The 

 banded character of the spectra of so many of these metalloids 

 has lent a really important argument to Mr. Lockyer in his bold 

 speculation as to their compound nature, in consequence of its 

 parallelism with the case of compound gases, and his hypothesis 

 has the merit of giving thus an explanation of the apparent 

 absence of elements that every argument would lead us to look 

 for, founded on a principle as ingenious as it is bold in^its appli- 

 cation. 



The recognition by Mr. Huggins in the spectra of the stars of 

 the lines belonging to hydrogen, sodium, magnesium, calcium, 

 and iron, and of carbon compounds in comets and nebulas, tends 

 strongly to confirm the probability of a general identity in the 

 chemical nature of the matter which pervades our universe ; and 

 further shows that the results of these investigations present 

 no obstacle to our drawing any conclusion to which the logic of 

 facts might otherwise guide us as to meteorolitic matter having 

 been in its origin foreign to the solar system. Observations by 

 v. Konkoly of the magnesium, sodium, and possibly also iron 

 lines in the August meteoric swarm, like those by Alexander 

 Herschel of the sodium line in those same St. Lawrence meteors, 

 are of value as extending the coincidence in the elementary con- 

 stitution of the sun, the stars, and meteorites, to those minuter 

 formsjof meteoric matter which,b y their dispersion in the atmo- 

 sphere, have hitherto been unattainable for the purposes of inves- 

 tigation. 



In passing from the merely elementary components of meteor- 

 ites to the chemical forms — that is to say, to the minerals in 

 which these elements are grouped in them, we find ourselves in the 

 presence of aggregates of crystallised minerals that at once remind 

 us of our terrestrial rocks. At a first aspect they might easily be 

 taken for rocks formed under conditions not very different from 

 those of our globe. A closer inspection, however, brings out dis- 

 tinctive characters in these that evidence a very different set of 

 conditions as having prevailed in the formation of the meteoric 

 and the terrestrial rocks. Without going into minute minera- 

 logical variations, and needlessly multiplying names, we may 

 tabulate in a very short list the constituent minerals of the different 

 sorts of meteorites. Several of these minerals are nearly identical 

 in composition and crystallographic character with corresponding 

 minerals met with in terrestrial rocks ; others again are unknown, 

 while some of them could hardly exist permanently as terrestrial 

 minerals ; and two present the composition of minerals familiar 

 to us in our own rocks, but crystallographically distinct from these 

 as belonging to different types of symmetry or ' ' systems " from 

 theirs. 



In the Elementary Condition. 



Iron xvith Nickel, traces of Cobalt and Copper, in some and 

 probably in all cases with Hydrogen, Carbonic oxide, or other 

 gases occluded in the metal. 



Carbon (graphitic and plumbaginous). 



Sulphur. 



Compounds, 

 Ferrous Sulphide [Troilite) FeS 



Magnetic Pyrites FcySg 



Magnesium Sulphide ? MgS 



Calcium Sulphide [Oldhamite) Ca(Mg)S 



A Titanium — Calcium Sulphide {Osbornite) ? 



Magnetite Fe304 



Chromite {FeCr)304 



Silica (orthorhombic as Asmanite) SiOg 



,, (hexagonal as Quartz) ? ) 

 Tin Oxide ) 



Silicates, viz. : — ■ 



Olivine varieties /Mg n Fe m-n^ 38104 



Enstatite MgSiOj 



Bronzite varieties /MgnFe m-nXSiOj 



\ m m / 



Augite varieties /MguCa m-nXSiOj 



\ m m / 



„ varieties containing corresponding ferrous silicate. 

 Anorthite CaAlgSiOs 



Labradorite ? 



„ in tesseral forms (Tschermak's Maskelynite). 



Schreibersite varieties (phosphides of iron and nickel). 

 Hydrocarbons (not yet sufficiently investigated). 



SnO, 



The names printed in italics are thus new to our mineralogy. 

 The mineral to which I originally gave the name of Oldhamite 

 is in all probability a mixture of two minerals — a Calcium Sul- 

 phide (which would be the pure Oldhamite) and a Magnesium 

 Sulphide ; and it is probable that they are not uncommon, 

 though sparsely scattered, ingredients in freshly fallen meteorites, 

 which, however, the action of a damp atmosphere rapidly de- 

 composes into calcium sulphate or carbonate, and free sulphur, 

 all which minerals occur in minute quantities occasionally, in 

 meteorites after they have been exposed to the weather. 



Until the year 1867 the mineralogical department at the 

 British Museum was without a laboratory, and chemical analyses 

 could not be performed. I accordingly had recourse in 1861 to 

 microscopic investigation as my only means of attacking the 

 mineralogical problems presented by meteoric rocks. By the 

 use of polarised light, of which the position of the plane of 

 polarisation was accurately determined, it was possible, by the 

 aid of an eyepiece goniometer and also of a revolving stage, to 

 determine with some precision the directions of the principal 

 sections in any of the minute sections of crystals which a frag- 

 ment of a meteorite worked down to a thin transparent slice 

 might present. Where such crystal sections happened to be 

 approximately parallel to a zone plane, and the traces of the faces 

 belonging to the zone could be seen with sufficient sharpness, or 

 where cleavage planes occurred parallel or at recognisable incli- 

 nations to faces of the zone, important decisions could be arrived 

 at by aid of polarised light. And this method is now becoming 

 one of great importance to petrologists. 



It was thus that I was enabled to anticipate with much con- 

 fidence the orthorhombic character of one and the clinorhombic 

 character of another ingredient (the enstatite and augite) in the 

 Busti meteorite, and determine the cubic character of the oldhamite 

 in that meteorite in 1862 ; and to be the first to announce the more 

 than probability of enstatite (including of course, as the term 

 then did, bronzite) being an important ingredient in meteorites ; 

 in the case of the Nellore meteorite in June 1863 and of that ot 

 Kaee in August 1864; a view confirmed afterwards (in November 

 1864) by Dr. Lawrence Smith on his repeating his analysis of 

 the meteorite of Bishopville, Of the meteorites of Busti and of 

 Manegaum, before they were cut, only minute fragments were at 

 my disposal ; and though in naming and first describing old- 

 hamite in 1862, I had spoken of it as having all the appearance 

 of being a " calcium galena," a small amount of probably sulphur 

 and gypsum that separated in the watch-glass in which I made a 

 qualitative investigation of it constrained me to say that I 

 believed it -to contain an excess of sulphur beyond that in the 

 neutral sulphide. 



Of the Manegaum meteorite also I employed only a minute 

 fragment for investigation, and I attributed the bronzite of that 

 meteorite to oUvine, the section of the crystal examined not 

 being really paralled to a zone-plane, and was confirmed in this 

 error by finding the powdered bronzite not to be insoluble in 

 acids. The addition of a laboratory to the department in 1867 

 enabled the long-desired analysis of the minerals I had separated 

 to be made ; and Dr. W. Flight being at my request appointed 

 chemical assistant, I was able, with the help of his analytical 

 skill, to complete the account of the minerals the presence of 

 which in the meteorites in question had been determined so 

 many years before. 



The separated sulphur in the oldhamite proved, when a 

 sufficient amount was taken for investigation, to be due to a 

 superficial decomposition ot the mineral, while bronzite was 

 shown to be distinctly soluble in acid. The methods I adopted 

 for the investigation of meteorites have since been employed by 

 other observers, as well in the mode of using the directions of the 

 principal sections of crystal-sections in the microscopic exami- 

 nation of terrestrial rocks as in the mode of attacking a meteo- 

 rite by separating and isolating by toilsome microscopic selection 

 its ingredient minerals ; the plan by which the silicates in the 

 Breitenbach siderolite and also those in fresh amounts from the 

 Busti aerolite had been separated with a view to analysis in 1864 

 and 1865. Viktor von Lang, to whose assistance and to whose 

 friendship I owe two or three of the most valued years of my 

 life, while he was my colleague, measured, and some time after- 

 wards published the account of the crystals of bronzite in the 

 Breitenbach meteorite ; the first occasion on which the crys- 

 tallography of that mineral had been made out, only the system 

 and approximate prism angle of the terrestrial bronzite and 

 enstatite being previously known through the optical researches 

 of Des Cloizeaux. 



The form of asmanite, the orthorhombic'variety of silica, occur- 



