5 So 



NATURE 



{Sept. 27, 1888 



NOTES ON METEORITES! 



III. 



Identity of Origin of Meteorites, Luminous 

 Meteors, and Falling Stars. 



TT is very fortunate for science that many of the meteorites so 

 ■^ carefully preserved in our museums have been seen to fall. 

 This being so we possess full accounts of the accompanying 

 phenomena and effects. 



These comprise the most vivid luminosity ; visible and audible 

 explosions, in some cases heard over thousands of square 

 miles of country, and at times a long train in the sky indicating 

 the meteor path, which sometimes remains visible for hours. 



Now precisely similar effects have been noted when nothing 

 has reached the earth's surface ; and in the thousands of records 

 of the phenomena presented by luminous meteors, fire-balls, 

 bolides, or shooting or falling stars as they have been variously 

 called, we have the links which connect in the most complete 

 manner the falls of actual irons and stones from heaven with the 

 tiniest trail of a shooting or falling star, tine etoile qui file, qui 

 file, et disparail. 



The heavy masses fall by virtue of their substance resisting the 

 friction of the air, the grains are at once burnt up and fill the 

 upper regions of the earth's atmosphere with meteoric dust. 



As we have seen, the weights of meteorites which have actu- 

 ally fallen vary between many tons and a few ounces, the latter 

 being, in all probability, fragments shattered by the explosion. 

 In the case of some shooting-stars, the actual weight involved 

 has been estimated by Prof. Herschel as low as two grains, not 

 one out of twenty estimated by hi in exceeding a pound. 



It may appear impossible that such atoms should produce the 

 brilliant effects observed, but Prof. Herschel has calculated that 

 a single grain moving at the rate of 30 miles a second represents 

 3. dynamical energy of 55,675 foot-pounds. This energy is con- 

 verted by the resistance of our grosser air into heat, as the motion 

 of a projectile is converted into heat by its impact on the target ;- 

 and hence the combustion of the matter of the meteorite, and 

 perhaps even the incandescence of the air through which it 

 rushes with such lightning velocity. This luminosity com- 

 mences often at a height of 80 miles, and sometimes even 

 higher, in regions where the atmosphere must be excessively 

 rare. 



Could these little bodies pierce our envelope as readily as do 

 their larger cousins, the meteoric stones and meteoric irons, we 

 should certainly have the advantage of placing them in our 

 museums ; but, on the other hand, the bombardment — the feu- 

 de ciel — might be one to which the feu-d'enfer of all terrestrial 

 artillery would be, in the gross total of results, as mere child's 

 play. 



But the identity of such phenomena as these is by no means 

 the only line of evidence demonstrating the connection now in 

 question. 



Proof from the Chemistry of Fire-balls. 



The spectral appearances observed with meteors, fire-balls, 

 and shooting-stars, which explode and produce luminous effects, 

 are entirely in harmony with those observations on the spectra of 

 meteorites to which I have referred. 



The observations, so far as they have gone, have given decided 

 indications of magnesium, sodium, lithium, potassium, and of 

 *ihe carbon flutings seen in comets. 



Prof. Herschel and Herr Konkoly have both noticed that in 

 the generality of cases the lines of magnesium (one of the 

 -constituents of the olivine) show themselves first in the or- 

 dinary meteor or falling star, and the beautiful green light which 

 is so often associated with these falling bodies is due to the 

 incandescence of the vapour of magnesium. 



The following quotations from Konkoly and Prof. Herschel 

 are among the authorities which may be cited for the above 

 statement : — 



" On August 12, 13, and 14 I observed a number of meteors 

 with the spectroscope; amongst others, on. the 12th, a yellow 

 fire-ball with a fine train, which came directly from the Perseid 

 radiant. In the head of this meteor the lines of lithium were 

 clearly seen by the side of the sodium line. On August 13, at 

 ioh. 46m. ios., I observed in the north-east a magnificent fire- 



1 Continued from p. 458. 



2 The particles of iron in a large projectile, after impact, which is accom- 

 panied by a flash of light, are usually brought to a dark blue colour, which 

 •would correspond to about 555° F.. but the momentary heat imparted is 

 certainly greater ihan rhis. 



ball of emerald-green colour, as bright as Jupiter, with a very 

 slow motion. The nucleus at the first moment only showed a 

 very bright continuous spectrum with the sodium line ; but a 

 second after I perceived the magnesium line, and I think I am 

 not mistaken in saying those of copper also. Besides that, the 

 spectrum showed two very faint red lines." x 



" A few of the green ' Leonid ' streaks were notic ed in No 

 vember (1886) to be, to all appearances, monochromatic, or quite 

 undispersed by vision through the refracting prisms ; from which 

 we may at least very probably infer (by later discoveries with 

 the meteor-spectroscope) that the prominent green line of mag- 

 nesium forms the principal constituent element of their greenish 

 light." 2 



Again, later on in the same letter, Prof. Herschel mentions 

 Konkoly's observation of the bright b line of magnesium, in 

 addition to the yellow sodium line, in a meteor on July 26, 1873. 

 I again quote from Prof. Herschel : — 



" On the morning of October 13 in the same year, Herr von 

 Konkoly again observed with Browning's meteor-spectroscope 

 the long-enduring streak of a large fire-ball, which was visible to 

 the north-east of O'Gyalla. It exhibited the yellow sodium line 

 and the green line of magnesium very finely, besides other 

 spectral lines in the red and green. Examining these latter 

 lines closely with a star-spectroscope attached to an equatorial 

 telescope, Herr von Konkoly succeeded in identifying them 

 by direct comparison with the lines in an electric Geissler-tube 

 of marsh-gas. They were visible in the star-spectroscope for 

 eleven minutes, after which the sodium and magnesium lines 

 still continued to be very brightly observable through the 

 meteor-spectroscope.'' 3 



An ither series of observations 4 gives continuous spectra for 

 the nucleus, and two trains with sodium, and a third with 

 sodium and a predominant green band, which was doubtless b of 

 magnesium, the meteor itself being of emerald-green colour. 



In cases where the temperature has been higher, the bright 

 line spectrum of iron has been associated with the bright lines 

 of magnesium in the spectrum of the falling star, so that the 

 two suiostances which are among the chief constituents of stones 

 and irons— precisely the two substances which we should expect 

 to find — are actually those which have been observed. 



The two lines which Konkoly supposes are probably due to 

 copper will, I expect, be found to be iron lines when other 

 observations are made of the spectra of meteors. 



These spectral appearances are naturally associated with 

 colours, and again we find that the colours of the trail, when 

 meteorites have fallen, closely resemble thjse observed when no 

 fall has been observed. 



Green is a tolerably common colour, especially in slow-moving 

 fire-balls about equal to Venus in lustre. These generally leave 

 a short trail of red sparks. 



About 10 per cent, of all shooting-stars show a distinct 

 colour, the most usual being orange or red, the slowly-moving 

 ones generally being red. The larger ones, or those with the 

 longest trails, often turn from orange to bluish-white, like burn- 

 ing magnesium. Sometimes the change is very sudden and 

 startling. 5 



A purple or mauve tint, like that given by copper, is sometimes 

 seen. 



Proof from the Aurora. 



When we come to consider the number of meteorites which 

 fall upon the earth daily we shall find that it is enormous ; and 

 this being so, if we can trace this dust in the air, or after it has 

 fallen, or both, if chemical examination shows it to be identical 

 with that of meteorites, we shall be supplied with another 

 argument which can be used in support of the fact that the 

 bodies which produce the dust are meteoric in their origin. 



One must suppose that these meteors in their passage through 

 the air break into numerous fragments, that incandescent 

 particles of their constituents, including nickel, iron, manganese, 

 and the various silicates of iron, are thrown off, and that these or 

 the products of their combustion eventually fall to the surface as 

 almost impalpable dust, among which must be magnetic oxide o 

 iron more or less completely fused. The luminous trains of 

 falling stars are probably due to the combustion of these innu- 

 merable particles, resembling the sparks which fly from a ribbon 

 of iron burnt in oxygen, or the particles of the same 



1 Ko-.koly, Obsei-vatory, vol. iii. 157. 



2 Herschel, letter to Nature, vol. xxiv. p. 507. 



3 Ibid. See also Astr. Nach., No. 2014. 



4 Monthly Notices, vol. xxxiii. p. 575. 



5 Corder, Monthly Notices, vol. xl. p. 13 



