164 



KNOWLEDGE. 



[September 1, 1891. 



stony constitnents together, or, as in the case of aeroHtes, 

 of stony minerals with no imcombined metals. The first 

 class, Sideritcs, contain from 80 to 95 per cent, of iiielcel- 

 iferons iron. The most important characteristic of the 

 first class is this constant association of nickel with the 

 iron, and the peculiar crystalline structure known as 

 Widnianstiitten's figures, which are revealed when a speci- 

 men is cut, polished, and then submitted to the action 

 of dilute nitric acid. A prominent peculiarity of the stony 

 Meteorites is their rhumh-itir structure, that is, they are 

 composed of round grains imbedded in a ground mass of 

 similar composition. 



All Meteorites have a varnish or glaze on the sur- 

 face, produced by their rapid passage through the air. 

 This glaze shows that the surface has been subjected to a 

 heat so intense as to fuse the material. The glaze is always 

 very thin, pointing to the fact that the heating has been of 

 very short duration, and has not had time to affect the 

 inner portions. 



Such are the chief features of the bodies which have 

 been seni to fall from the sky. Now and again, in different 

 parts of the globe, specimens are found on the surface 

 which show the same well-known characters. These frag- 

 ments are often found at a distance fi-om any rocks having 

 the least resemblance to them in mineralogical character, 

 and where there is no evidence of transport by ice or water 

 as in the case of boulders. Such specimens are placed in 

 museums under the class " Meteorites," and in many 

 instances the evidence is sufficiently cogent to leave 

 no practical doubt of their origin being identical with 

 that of the Meteorites the fall of wliich has been actually 

 observed. 



A very slight examination of the circumstances attend- 

 ing the fall of Meteorites, as. <■.</., their high velocity, is 

 sufficient to show that they are not ordinary falling bodies, 

 but that they have come from regions outside the Earth's 

 atmosphere. Whether their ultimate origin is terrestrial, 

 or from some other member of the solar system, or from 

 regions beyond that system, it is not so easy to decide. 

 The %-iew which finds most general acceptance is that the 

 Meteorites, like certain systems of shooting stars, move in 

 orbits similar in form and range to those of the comets. 

 Their supposed ex-terrestrial origin gives a certain fasci- 

 nation to the study of Meteorites. Viewed in the light of 

 visitors from other worlds than ours, the comparison of 

 their materials with the materials of our own earth 

 becomes a matter of the highest interest. Hitherto, some 

 four-and-twenty of the already-known chemical elements 

 have been recognised in Meteorites, and no new element 

 has been found in them. The principal elementary con- 

 stituents are — 



Iron, Phosphorus, 



Nickel, Sulphur, 



Magnesium, Carbon, 



Calcium, Oxygen, 



Aluminium, Silicon. 



The following occur in smaller quantities : — 



Cobalt, Titanium, 



Manganese, Lithium, 



Chromium, Sodium, 



Copper, Potassium, 



Tin, Hydrogen, 



Antimony, Nitrogen, 



Arsenic, Chlorine. 



Of these nitrogen and hydrogen occur in the uncombmed 

 state as occluded gas. Carbon occurs nncombined, as 

 graphite, as well as combined with oxygen. The following 

 is a list of the mineral species which have been identified 

 in Meteorites with the chemical formulie as given by 



P. Groth [Ohersiijht der Minm-alien). The names in italics 

 indicate species which have not been recognised among 

 naturally-occurring terrestrial minerals. Of these Schrei- 

 bersite,Lawrencite,Rhabdite and Troilite have been repro- 

 duced in the laboratory. 

 Anorthite. Si,, Al 0,, Al Ca. 

 Augite and Diopside (Si O.j)^ Mg Ca ; or, 



(Si Oj); (Mg, Fe! Ca. 

 Breunnerite, C 0^ (Mg, Fel. 

 Chromite [(Cr, Fe) 0„] (Fe, Cr). 



ThtuhreeUte (Cr S^)., Fe (crystalline form not deter- 

 mined). 



Enstatite and Bronzite (Mg, Fe) Si O3. 

 Hornblende I Si O.j)., (Mg, Fe), Ca (Si Os)o ) 

 (Si 0.^)1 (Mg, Feij AL (Al O^r j 

 Labradorite, Si, Si Og Al Na. ) 

 Sio" Al Os Al Ca. 3 

 Lairmicite, Fe CU. 



Readily prepared in the laboratory, but rapidly 

 oxidizes, hence probably its non-occurrence in 

 nature under ordinary conditions. 

 Magnetite (Fe 0.,), Fe. 

 Ma^Miinite [Si 6']^ Al, (Ca Na.^ K„). 

 Crystallizes in the cubic system. 

 Oldhiwite, Ca S. 



A readily oxidizable body, not occurring in nature 

 under ordinary conditions. 

 Olivine, Si O, (Mg, Fe)„. 

 (himniite. 



? An oxysulphide of Titanium and Calcium. 

 Pvrrhotite, Fen Sp. 

 lihohdite, Fe- P. 



Reproduced by passing the vapour of Phosphorus 

 over red-hot iron-wire. Crystallizes in the 

 quadratic system. 

 S,-hrnhersite, ? (Fe Ni 00)3 P. 

 TrniUti', Fe S. 



Apparently identical with the product obtained by 

 heating together iron and sulphur. Crystal- 

 line form not determined. 

 Trydimite, Si O,. 



Trydimite is a form of silica not produced in 

 presence of water (as quartz), liut by igneous 

 fusion. 

 Graphite. 



Alloys of Nickel and Iron. 



Hydrogen, nitrogen, carbonic acid and carbonic oxide 

 as occluded gases. 



Certain soluble salts, occasionally, as the chloride ajid 

 sulphate of sodium, and the sulphates of calcium and 

 magnesium. 



The first information as to the mode of formation of the 

 minerals occurring in Meteorites was afiorded by the 

 researches of Dr. Sorby. He made use of the method of 

 studying the inrhixiom which may be seen in crystals when 

 examined in thin section under the microscope, a high 

 power being generallj- used (y. J. Geol. Soc, 1858). By 

 the study of artificially produced crystals, he established 

 the following facts : — 



1. That when substances crystallize out from aqueous 

 solution portions of the liquid are included in the crystal, 

 forming liquid cavities or inclusions. If the crystal- 

 lization take place at a high temperature the liquid on 

 cooling contracts, leading what is generally termed a gas 

 bubble. This bubble is free to move. Sometimes the 

 bubble is vacuous, sometimes it contains a gas such as 

 carbonic acid found in the cavities in quartz. 



2. When the nature of the liquid magma, from which 

 a substance crystallizes is such that it solidifies at the 



