Aprils, 1877] 



NATURE 



497 



minute particles when they were probably in a separate 

 state, mechanical forces of great intensity would be re- 

 quired. By far the greater number of meteorites have a 

 structure which indicates that this breaking up of the 

 constituents was of very general occurrence. 



Assuming then that the particles were originally de- 

 tached like volcanic ashes, it is quite clear that they were 

 subsequently collected together and consolidated. This 

 more than anything else appears to me a very great diffi- 

 culty in the way of our adopting Reichenbach's cometary 

 theory. Volcanic ashes are massed together and con- 

 solidated into tuff, because they are collected on the 

 ground by the gravitative force of the earth. It appears 

 to me very difficult to understand how in the case of a 

 comet there could be in any part a sufficiently strong 

 gravitative force to collect the dispersed dust into hard 

 stony masses like meteorites. If it were not for this 

 apparent difficulty we might suppose that some of the 

 facts here described were due to the heat of the sun, when 

 comets approach so near to it that the conditions may be 

 practically almost solar. Comets may and probably do 

 contain many meteorites, but I think that their structure 

 indicates that they were originally formed under con- 

 ditions far more like those now existing at the surface of 

 the sun than in comets. 



The particles having been collected together, the com- 

 pound mass has evidently often undergone considerable 

 mechanical and crystalline changes. The fragments have 

 sometimes been broken in situ, and "faulted;" and 

 crystalhsation has taken place, analogous to that met with 

 in metamorphic rocks, which has more or less, and some- 

 times almost entirely, obliterated the original structure. 

 The sin»plest explanation of this change is to suppose that 

 after consolidation meteorites were variously heated to 

 temperatures somewhat below their point of fusion. Those 

 which have the structure of true lava may in some cases 

 be portions which were actually remelted. We have also 

 this striking fact, that meteoric masses of compound 

 structure, themselves made up of fragments, have been 

 again broken up into compound fragments, and these 

 collected together and consolidated along with fresh mate- 

 rial, to form the meteorites in their present condition. 

 L'Aigle is a good example cf this complex structure. 



Another remarkable fact is the occurrence in some 

 meteorites of many veins filled with material, in some 

 respects so analogous to the black crust, that at one time 

 I felt induced to believe that they were cracks, into which 

 the crust had been injected. Akburfur is a good example 

 of this, and seems to show that under whatever condi- 

 tions the veins were found, they were injected not only 

 with a black material, but also with iron and magnetic 

 pyrites. 



Taking, then, all the above facts into consideration, it 

 appears to me that the conditions under which meteorites 

 were formed must have been such that the temperature 

 was high enough to fuse stony masses into glass; the 

 partic'es could exist independently one of the other in an 

 incandescent atmosphere, subject to violent mechanical 

 disturbances ; that the force of gravitation was great 

 enough to collect these fine particles together into solid 

 iras^e?, and that these were in such a situation that they 

 COL Id be metamorphosed, further broken up into frag- 

 ment;--, and again collected together. All these facts 

 agree so admirably with what we know must now be 

 taking place near the surface of the sun, that I cannot 

 but think that, if we could only obtain specimens of the 

 sun, we should find that their structure agreed very 

 closely with that of meteorites. Considering also that 

 the velocity with which the red flames have been seen to 

 be thrown out from the sun is almost as great as tha 

 necessary to carry a solid body far out into planetary space, 

 we cannot help wondering whether, after all, meteorites 

 may not be portions of the sun recently detached from it by 

 the violent disturbances which do most certainly now occur, 

 or wae carried off from it at some earlier period, when 



these disturbances were more intense. At the same time, 

 as pointed out by me many years ago, some of the facts 

 I have described may indicate that meteorites are the 

 residual cosmical matter, not collected into planets, formed 

 when the conditions now met with only near the surface 

 of the sun extended much further out from the centre of 

 the solar system. The chief objection to any great ex- 

 tension of this hypothesis is that we may doubt whether the 

 force of gravitation would be sufficient to explain some 

 of the facts. In any case I think that one or other of 

 these solar theories, which to some extent agree with the 

 speculations of the la^e Mr. Brailey, would explain the 

 remarkable and very special microscopical structure of 

 meteorites far better than that which refers them to por- 

 tions of a volcanic planet, subsecpently broken up, as 

 advocated by Meunier, unless indeed we may venture to 

 conclude that the material might still retain its original 

 structure, due to very different conditions, previous to its 

 becoming part of a planet. At the same time so little is 

 positively known respecting the original constitution of 

 the solar system, that all these conclusions must to some 

 extent be looked upon as only provisional. 



I will now proceed to consider some facts connected 

 with meteoric irons. The so-called Widmanstatt's figur- 

 ing, seen when some of these irons are acted on by acids, 

 is well known ; but in my opinion the preparations are 

 often very badly made. When properly prepared, the 

 surface may be satisfactorily examined with a magnifying 

 power of 200 linear, which is required to show the full 

 detail. We may then see that the figuring is due to a 

 very regular crystallisation, and to the separating out one 

 from the other of different compounds of iron and nickel, 

 and their phosphides. When meteoric iron showing this 

 structure is artificially melted, the resulting product does 

 not show the original structure, and it has therefore been 

 contended that meteoric iron was never in a state of 

 igneous fusion. In order to throw light on this question, 

 I have paid very much attention to the microscopical 

 structure of nearly all kinds of artificial irons and steels, 

 by studying surfaces polished with very special care, so as 

 to avoid any effect like burnishing, and then acting on 

 them very carefully with extremely dilute nitric acid. In 

 this manner most beautiful and instructive specimens 

 may be obtained, showing a very great amount of de- 

 tail, and requiring a magnifjing power varying up to at 

 least 200 linear. In illustration of my subject I will call 

 attention to only a few leading types of structure. In 

 the first case we have grey pig-iron, showing laminae of 

 graphite promiscuously arranged in all positions, on the 

 surface of which is a thin layer of what is probably iron 

 uncombined with carbon, whilst the intermediate spaces 

 are filled up with what arc probably two different com- 

 pounds of iron and carbon. 



White chilled refined iron has an entirely different 

 structure and more uniform crystallisation, the structure 

 is very remarkable and beautiful, mainly due to the vary- 

 ing crystallisation of an intensely hard compound of iron 

 and carbon, and the two other softer compounds met 

 with in grey pig. 



Malleable bar iron has an entirely different structure, 

 and shows fibres of black slag, and a more or less uniform 

 crystallisation of iron with a varying small amount of 

 carbon. 



Cast steel differs again very much, from any of the 

 previous. It shows a fine-grained structure, due to small 

 radiating crystals, and no plates of graphite. 



The diflerence between any of the above and meteoric 

 iron is extremely great. 



In the case of Bessemer metal we have a crystalline 

 structure approaching in some places more nearly to that 

 of meteoric iron. We see a sort of Widmanstatt's figuring, 

 but it is due to the separation of free iron from a com- 

 pound containing a little carbon, and not to a variation in 

 the amount of nickel. 



The nearest approach to the structure of meteoric iron 



