Oct, 7, 1875] 



NATURE 



505 



will dissolve meteoric iron out of it ; but the remainder of the 

 mass will, after this treatment, in most cases, crumble into a 

 granular powder, showing that the cohesion of the mass is not 

 like that of an ordinary terrestrial rock. Some aerolites, again, 

 will even crumble in the fingers without previous treatment. 



The rocks to which they bear the nearest resemblance, in 

 respect of their mechanical structure, among the products of our 

 volcanoes, are some volcanic bombs, and, as regards several of 

 the aerolites, certain kinds of volcanic tufa. 



Now, in examining these bodies more closely, the first thing that 

 calls for attention is that they are composed entirely, or almost 

 entirely, of crystalline substances ; and that matter thus coming 

 from regions beyond our world crystallises in the same way, and 

 is obedient to the same law, as matter which crystallises on 

 the globe. 



Sections of meteorites cut thin and ground down to transparent 

 slices, when examined by means of polarised light, are seen to 

 be crystallised throughout ; the crystalline character of the 

 substances being evidenced by the interference lints which colour 

 the different crystals of which the sections are made up. 

 Another characteristic of many meteorites, in which they differ 

 from ordinary terrestrial rocks, is what has been termed by 

 Gustav Rose their chondritic structure. The minerals in these 

 are found to be more or less aggregated in little spherules, which 

 are distributed in different degrees of abundance in different 

 meteorites through the ground-mass of the stone. 



Sections of chondritic meteorites show them to consist in some 

 cases almost entirely of spherules. Such is the case with the 

 Parnallee aerolite, of which the most varied groups of spherules 

 may be seen assembled in a single section. Some of these 

 spherules are encased, as it were, in minute shells of metallic 

 (nickeliferous) iron, or of such iron mingled with a kind of 

 pyrites peculiar to meteorites, an iron sulphide termed troilite, 

 constituted by an equivalent of sulphur combined with one equi- 

 valent of iron. Minute granules of troilite and iron, without 

 any definite form, are so seen to be disseminated among the 

 grains of the interspherular ground-mass of the meteorite. 



A closer inspection of the spherules further reveals in many 

 cases the presence of /w/r^rspherular iron. In some spherules the 

 meteoric silicates may be seen, radiating from a point, but while 

 the spherule is enclosed in a mixed outer mass of silicates, iron 

 and troilite in little black specks are seen scattered all through 

 it, presenting the appearance of having been spurted, as it were, 

 from a point, the larger particles to the greater distance : and 

 these specks consist in part of nickeliferous iron, while some are 

 meteoric pyrites (troilite). 



In connection with the subject of these spherules, which form 

 so characteristic a feature of many stony meteorites, it should be 

 mentioned that occasionally some of the spherules are seen to 

 be broken in half and the halves separated from each other to 

 some small distance, a fact of considerable significance, though 

 not easy of interpretation in connection with the history of the 

 meteorite and the more or less violent crises it must have passed 

 through at successive periods in that history. 



Evidence of another kind of historical succession in the events 

 and influences through which a meteorite may have passed is 

 afforded by the not rare peculiarity of a sort of vein, like a 

 mineral vein, running through the meteorite. In fact, just as in 

 a mine one may meet with a fissure that, once dividing the 

 ** country," but subsequently filled by rocky matter, cuts across 

 the course of a mineral vein which itself was originally formed 

 in a similar way ; and just as such a cross fissure thus inter- 

 secting with the original metalliferous vein often gives us evidence 

 of a hcaze, i.e. that one side of the new, fissure has slid upwards 

 or downwards along the other, so an exactly similar thing is met 

 with in meteorites, and is admirably ieen in the microscopic 

 sections of them. 



Such a fissure will sometimes divide several spherules lying on 

 its track, the two sides of the fissure having slid, the one along 

 the other. The corresponding halves of the spheniles are in 

 such cases separated to some distance along the fissure, and this 

 is itself filled with the vein of meteoric iron or troilite, in some 

 cases with a black fused substance, like the cnist of a meteorite. 



In passing next to the consideration of the chemistry of meteo- 

 rites, one of the first inquiries that suggests itself is whether and 

 to what extent the elementary composition of these cosmical 

 rock-fragments accords with that of our own world, or with the 

 revelations which the prism has afforded us regarding the consti- 

 tution of the matter in energetic action on the surface of our sun, 

 or of those far distant suns, the stars ; or, again, in those still 

 uninterpreted assemblages of luminous matter that we call the 



nebulae. Now, the elements that have been already recognised 

 by analysis as existing in meteorites form a list that comprises 

 one-third of all the elements known to our chemistry ; and these, 

 the more abundant elements on our world. They are — 



Hydrogen Chromium Arsenic 



Lithium Manganese Vanadium ? 



Sodium Iron Phosphorus 



Potassium Nickel Sulphur 



Magnesium Cobalt Oxygen 



Calcium Copper Silicon 



Aluminium Tin Carbon 



Titanium Antimony Chlorine 



Now, of these elements, those in italics have also been found 

 by the spectroscope to be constituents of the solar surface, 

 together with zinc, strontium, and cadmium, which metals have 

 not yet been met with in meteorites. 



The number of elements recognised as existing in activity on 

 the solar orb will undoubtedly be largely increased with the pro- 

 gress of the combined study of the solar spectrum and of the 

 conditions under which the several lines belonging to the diffe- 

 rent elements are developed. It is by study of this kind that 

 Mr. Lockyer has detected potassium in the sun. The fact that 

 at the present time all the elements detected in the sun excepting 

 three are met with in meteorites, while on the other hand the 

 meteorites contain five metals not as yet found in the sun, at the 

 same time that the six metalloids found in them are so strangely 

 all apparently absent from the surface of our great luminary, 

 might seem to place difficulties in the way of our recognising a 

 general unity of elementary composition in the matter that com- 

 poses the various orbs and wandering masses that pervade our 

 universe. 



But it is clear, on the other hand, that it is too early as yet to 

 look on these results as establishing even probable exceptions to 

 such a unity. 



That carbon, sulphur, potassium, and phosphorus^ elements so 

 frequently met with in meteorites and on our globe, should, with 

 nitrogen, be absent or have escaped detection among the elements 

 involved in the active operations on the surface of the sun, is 

 certainly not a little surprising. Nor is the failure of the prism to 

 detect the lines due to oxygen and silicon among those presented 

 by the solar photosphere to be accounted for by assuming the 

 persistency of particular silicates in resisting decomposition or 

 vaporisation even in a solar temperature, for Von Rath has 

 shown that silicates such as augite and leucite are actually depo- 

 sited by a process of sublimation even at the comparatively low 

 temperatures of our volcanoes. Yet it is difficult to believe that 

 the last-mentioned elements can be absent from the great 

 central body of our system, whether we reason from analogy, 

 from their great importance in the composition of our earth, or 

 from the more than probability that these elements must have 

 been contributed to a large amount to the material of the sun 

 by meteoric matter falling into his surface. 



Mr. Lockyer has indeed grasped this difficulty with a bold 

 hand, and has not hesitated to declare as a probable explanation 

 of the results obtained from the spectra of the reversing layer and 

 chromosphere of the sun, that the elements exist there not in a 

 molecular but in an atomic condition ; and he further assumes 

 that the metalloids exist in a more simple elementary condition 

 than that in which we know them ; their terrestrial existence 

 being assumed to be that of compounds which have yet to be 

 resolved into their constituents by our chemistry, though under 

 the fierce chemistry of the sun it is only as thus resolved 

 that they exist on his surface. It is startling for the chemist 

 to be thus called upon to believe that enormous temperatures 

 are endowed with a dissociating power, capable of not 

 merely severing the bonds of ordinary chemical combination, 

 but further of forcing into a condition of ultimate atomic disin- 

 tegration composite molecules where these are the form under 

 which the chemist has learnt to recognise the ordinary condition 

 of even the isolated elements. Certainly the concordance of 

 the heights to which the different gaseous elements rise in the 

 reversing layer with the weights of the atoms of those elements 

 as represented by their equivalents in the older chemistry, would 

 lend something more than a justification to the even bolder 

 hypothesis that recognises in the metalloids (such as silicon, 

 sulphur, and oxygen, as they exist in our world) compounds of 

 other and to our chemistry unknown elements, were we able to 

 assert that the gaseous molecules of the metals in question, other 

 than hydrogen, potassium, and sodium, must necessarily, like 

 those of these elements, be dfiible. It would be, in any case, a 



