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NATURE 



\Oct. 14. 187 



the other hand the silicates composing meteorites, and those 

 constituting the mass of our terrestrial rocks, are alike almost 

 devoid of nickel ; and a process that would reduce the iron in 

 such rocks {e.g. serpentine or Iherzolite) as contain traces of this 

 element would' simultaneously reduce the nickel also to the 

 metallic condition, as has been shown by Daubree. 



Among those who have sought to throw light on the part of 

 our problem which deals with the chemical history of meteorites, 

 M. Daubree, the distinguished Director of the Ecole des Mines, 

 stands forward. He has subjected both meteorites and certain 

 terrestrial rocks in some respects mineralogically allied to them to 

 fusion under special conditions. He has, further, reviewed in a 

 valuable article in the Comptes Rendus of the French Academy, 

 the two opposite chemical conditions under which aerolitic matter 

 may be supposed to have assumed its present form ; those namely, 

 first, of the oxidation with a limited supply of oxygen of the 

 elements composing a meteorite assumed as combined inter se ; 

 and secondly, a condition under which a basic ferruginous silicate 

 may be supposed to be converted into a neutral silicate with the 

 emancipation of free iron by the operation of reducing agents, 

 such as hydrogen or carbon, acting on the ferrous silicate at a 

 high temperature. 



In this way an olivine, rich in diferrous silicate, would become 

 a bronzite poor in ferrous silicate, or become an enstatite without 

 any iron in it at all, the iron lost in either case by the olivine 

 being separated as metallic iron ; and M. Daubree performed 

 transformations of this kind. 



Now, the remarkable discovery by the late Prof. Graham of 

 hydrogen in the Lenarto iron, and that recently made by Wohler 

 of carbonic oxide in the iron of Ovifak (due, however, probably 

 in this case to the action of magnetic iron-oxide on the carbon 

 of the meteorite), and also by Prof. Mallet of the same gas in a 

 meteoric iron from Virginia, lend some probability to the view of 

 M. Daubree. 



Still the existence of great masses of siderolites like those of 

 Pallas and from Atacama, rich in ferruginous olivine, and pre- 

 senting, so far as the analyses may be trusted, no trace of ensta- 

 tite, or even bronzite, offers a great obstacle to the view that the 

 iron in these cases was the result of a reduction from olivine. 

 So again the Breitenbach siderolite, notwithstanding its large 

 ingredient of free silica (as asmanite) consists largely of a bronzite 

 very rich in ferrous monosilicate. This bronzite, however, it is 

 to be said, resists the reducing action of hydrogen at a considerable 

 temperature. 



The similarity, not to say the peculiarity, as well in their chemical 

 nature as in their mechanical condition that 1 have alluded to as 

 characterising so many meteorites would seem to impose some 

 restrictions on our freedom in tracing the origin of these bodies to 

 distant and dissevered regions of interstellar space. And, indeed, 

 though a great unity and simplicity in condition and in material 

 Avould seem to rule throughout thestellar universe, as viewed by our 

 present means of knowledge, and so far would justify our treating 

 lightly the sameness of the meteoric material that reaches us as a 

 check on our reasonings ; yet it is to be borne in mind that the 

 prism has only begun to interpret for us the language of the stars, 

 and that further research may introduce complexity, and narrow 

 the limits of our problem. On the other hand, we can only 

 reason legitimately from the standing-point of the present ; and 

 it is equally probable, nay, almost certain, that the stellar 

 spectra, in wnich, for instance, the lines characterising nickel 

 have not yet been found, will, on direct search for them, yield 

 those lines, and then the arguments otherwise converging on the 

 probability of meteorites coming to us from interstellar space will 

 acquire an almost conclusive character ; for the difficulties in the 

 way of our confining their origin to our own solar system are 

 almost insuperable. Their high proper velocity, often far greater 

 than that ot the earth in her orbit, the directions of their motion, 

 sometimes direct, often retrograde, and continually at high angles 

 to the ecliptic, are not consistent with their being portions of 

 asteroidal matter sporadically dispersed, while they are still less 

 so with any explanation of meteorites as resulting from lunar 

 volcanoes or from any lost telluric satellite, or from satellitic 

 matter that had escaped the centralising influence of gravitation. 



Whether any of the meteorites are intercepted by our earth 

 while passing nodes common to our orbit, and to long cometary 

 orbits described by innumerable meteoric groups around the sun, 

 is a question we cannot answer in the present condition of our 

 knowledge. 



But reasoning by analogy from the movements of the meteor- 

 swarms that we are acquainted with, this is rendered highly proba- 

 ble by the identification beyond a question of the orbits of periodic 



meteor-swarms with those of known comets, and the statement of 

 Leverrier that these meteor-swarms are probably vast cosmical 

 clouds consisting of sparsely-spread particles ; and that some 

 of them entering our solar system from interstellar space have been 

 drawn aside by planetary attraction, and have assumed a circum- 

 solar orbit. When the curve is an ellipse, they of course remain in 

 our system, and are seen now as comets, or also again in certain 

 very rare instances, where their orbit intersects with our own, as 

 star-showers, which recur annually, or at the long intervals sepa- 

 rating tlieir approach to their perihelia, according as they have 

 or have not been long enough members of our system for 

 the meteoric dust to have become more or less equally distributed 

 along their orbit in a ring, or have still only the form of a pro- 

 longed cloud continually becoming more and more annular in the 

 distribution of its ingredient particles. 



Four cases of unquestionable accordance between comets and 

 meteor showers are established in — 



The Lyriad meteoric shower (April 20-21) and Comet I. of 

 1 86 1 (Galle and Weiss). 



The Perseids meteoric shower (August lo-ii) and Comet III. 

 of 1862 (Schiaparelli). 



The Leonids meteoric shower (November 13-14) and Comet I. 

 of 1866 (Oppolzer, Peters, and Schiaparelli). 



The Andromedes meteoric shower (November 27-28) and 

 Biela's Comet (Galle and Weiss). 



If we imagine meteorites to have a similar history, but with 

 the difference that the meteor-particles are assembled into larger 

 masses or clusters of them, and that these consequently are sepa- 

 rated from each other by far vaster distances than is the case with 

 the even widely-spread units that compose a meteor- swarm, we 

 may comprehend why the meteorite is such a rare visitant 

 as compared with the meteors proper, of which thousands 

 must pass into our atmosphere every hour. Indeed, when 

 we consider what has been before alluded to, touching the com- 

 paratively loose condition of aggregation of so many meteorites, 

 and when we remember that the fine dust and little particles of 

 a meteoric cloud are separated by no such atmosphere, gaseous 

 or vaporous, as prevents actual contact between surfaces on a 

 terraqueous globe, we may perhaps go so far as to suppose that if 

 groups of the individual particular units of a meteor cloud once 

 should approach each other to a distance small enough to give 

 their mutual gravitation a sensible influence, they might gradually 

 collect into masses, and acquire a cohesion more or less compact 

 according to the conditions imposed on such masses during their 

 subsequent history. Such is possibly the case with the nuclei of 

 the comets, which would thus possess the character of a cluster 

 of meteorites, while the coma is composed of meteoritic particles 

 of the character of ordinary meteors. 



There is one respect in which the comparison of the smaller 

 meteors with those of greater magnitude and with meteorites 

 may seem to point to a difference of some importance in the 

 character of the objects themselves. The velocities usually as- 

 cribed to the former class of bodies are in many cases very much 

 higher than that belonging to the larger objects. Thus, a velo- 

 licity of 140 miles per second has been ascribed to some of the 

 smaller meteors. Mr. Hind, however, gives the perihelion 

 velocity of the August swarm at 26 miles per second, which, 

 added to the motion of the earth (as the meteors are retrograde), 

 would give a velocity of about 40 miles at a point so near their 

 perihelion as that in which our earth meets them. On the other 

 hand, a velocity of from 13 to 40 miles per second is that usually 

 ascribed to the larger meteoric masses, and to meteorites of 

 which the actual fall has been witnessed. 



Furthermore, we have to consider, on the one hand, the very 

 great difficulty in determining the parallax of a body moving so 

 rapidly in the absence of accurate instrumental means of observ- 

 ing it, and on the other hand, the fact that a large meteoric mass 

 is sure to be observed best, and by daylight almost exclusively, 

 during the more brilliant and imposing, and therefore the nearer 

 and more slowly traversed, portion of its track. Thus the small 

 particles represented by the ordinary meteor are kindled and 

 extinguished almost instantaneously in the upper part of the atmo- 

 sphere, while themeteoroid masses of larger volume are observed 

 and reasoned upon almost entirely during the more imposing 

 part of their course, namely, their passage through its lower and 

 denser regions. 



While, then, we are restrained by the facts, as they at present 

 stand, from separating into different classes of cosmical pheno- 

 mena the meteors and the meteoroid bodies known as fireballs and 

 meteorites, and I must add the comets, so are we constrained 



