6o 



NA TURE 



{Nov. 17, 1887 



ihe north-east of 0'G}alla. 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 lo an equatorial 

 telescope, Herr von KonKoly succeeded in ideniifying 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 ihe 

 meteor-spectroscope."' 



The green line "6" of magnesium occurring as a bright 

 line in luminous meteors indicates that their temperature when 

 passing through our atmosphere is higher than that of the 

 bunsen, and we may add of comets as generally observed, 

 although some exhibit the /^ lines of magnesium and those of 

 iron when at perihelion, as shown later on. 



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. 



The main conclusions from this comparison are then : ,(i) that 

 the temperature of luminous meteors is higher than that of the 



bunsen flame ; (2) that the meteorites which produce the phe- 

 nomena we are now discussing are hotter than those in the 

 experimental gliw taken generally ; and (3) that in both cases 

 finings of carl on may be seen. 



$. Comets. 



When the meteorites are strongly heated in a glow-tube, the 

 whole tube when the electric current is passing gives us the 

 spectrum of carbon. 



When a meteor-swarm approaches the sun, the whole region 

 of space occupied by the meteorites, estimated by Prof. 

 Newton in the case of Biela's comet to have been thirty miles 

 apart, gives us the same spectrum, and further it is given by at 

 all events part of the tail, which in the comet of 1680 was 

 calculated to be 60,000,000 miles in length. The illumination 

 therefore must be electrical, and possibly connected with the 

 electric repulsion of the vapours away from the sun ; hence it is 

 not dependent wholly upon collisions. 



Passing now from the flutings seen in cometary spectra, it is 

 found that most of the lines which havebeen observed at perihelion 

 are coincident with lines seen in experiments with meteorites, 



Map 3. — Comparison of flutings seen in the spectra of " stars " and comets with flutings of carbon, manganese, and zinc ; and, in the case of R Geminorum, 

 lines With remnants of flutings and hnes seen in a meteorite glow. (The Zn fluting is at \ 544 in a Oiionis.) 



while the low temperature lines of Mg are absent. In the great 

 comet of 1882, to which particular attention has been given on 

 account of the complete record of its spectrum by Copeland,^ 

 the lines recorded were the D lines of sodium, the low-tempera- 

 ture iron lines at 5268, 5327, 5371,5790, and 6024, the lines seen 

 in the manganese spectrum at the temperature of the bunsen 

 burner at 5395 and 5425, and a line near b which might be due 

 to magnesium, or to a remnant of the carbon fluting. In addi- 

 tion to these there was a line at 5475, probably due to nickel, 

 the absence of the blue strontium line indicating that it is not 

 likely to be the green line of strontium. There were also four 

 other lines less refrangible than D, the origin of which has not 

 yet been determined. As the comet got further from perihelion 

 the lines gradually died out, those which remained longest being 

 the iron line at 5268 and the line near b. The absence of D 

 before the disappearance of all the lines is probably to be 



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

 '■^ Copernicus, vol. ii. p. 234. 



accounted for partly by the greater brightness of the continuoi 

 spectrum in that region. 



In the comets of 1866-67, when seen away from the sur 

 the only line seen was the one at 500.'' 



It is fair to myself to say that I was not aware of thes 

 observations when I began to write this paper. The fact of \}n\ 

 line at 500 remaining alone in Nova Cygni made it clear that q 

 my views were correct, the same thing should happen wiif 

 comets. It now turns out that the crucial observation which ' 

 intended to make was made twenty years ago. 



' " In January 1S66 I communicated to the Royal Society the result of an 

 examination of a small comet visible in the beginning of that year(Proc. K.S. 

 vol. XV. p. 5). I examined the spectrum of another small and faint comet in 

 May 1E67. The spectra < f these objects, as far as their feeble light permitted 

 them to be observed, appeared to be very similar. In the case of each of 

 these comets the spectrum of the minute nucleus appeared fo consist of a 

 bright line between b and F, abcut the position of the double line of the 

 spectrum of nitrogen, while the nebulosity surrounding the nucleus and 

 forming the coma gave a sptc;riim which was apparently caitinuous'' 

 (Huggins, Proc. R.S. vol. xvi. p. 387). 



.^i 



