342 



NATURE 



[August 7, 1890 



The Perseid Meteor Shower. 



With reference to the letter of Mr. Monck in Nature of 

 July 24 (p. 296), I would remark that his attempted explanation 

 of the displacement in the Perseid radiant point is altogether 

 futile. If your correspondent were better acquainted with the 

 facts in detail, I think he would readily admit this. 



My observations in this branch have been effected in the hope 

 that they might prove useful, and I am sorry to see that Mr. 

 Monck has so thoroughly misapprehended them. The shifting 

 radiant of the Perseids is fully proved, and anyone who will take 

 the trouble to watch the sky at the proper season may readily 

 observe the fact for himself. W. F. Denning. 



Bristol, August 2, 1890. 



COMPARISON OF THE SPECTRA OF NEBULA 

 AND STARS OF GROUPS I. AND II. WITH 

 THOSE OF COME TS AND A UROR^. 



I. 



THE first step towards my present views as to the 

 evolutions of the various groups of cosmical bodies 

 was taken when one day I was attempting to trace the 

 origin of the absorption flutings in stars of Vogel's Class 

 \\\.a. So far, no one had endeavoured to trace their 

 origin, all the work having been confined to the absorp- 

 tion lines. It is true that both Dr. Huggins and Vogel, 

 as well as others, had published maps of the spectra of 

 these stars, showing the absorption flutings as well as 

 the lines, but the origins of the former were not inquired 

 into. 



It was at once perfectly obvious that among the chief 

 absorption flutings were the most prominent of those seen 

 in the spectrum of manganese at the temperature of the 

 oxy-coal-gas flame— a temperature at which only one line 

 is visible, while in the sun all the lines of manganese are 

 visible. In order to investigate this further all the 

 flutings seen when the principal metals were exposed to 

 this temperature were mapped, with a view of determining 

 whether any others besides those of manganese were 

 visible in the stellar spectra. Several others, notably one 

 of lead, were found to be present. 



Here, then, was proof positive of low temperature ; 

 from solar absorption to the absorption of these stars of 

 Class \\\.a we passed from phenomena which we can 

 reproduce at the temperature of the arc to those visible 

 at the temperature of the oxy-coal-gas flame. 



It was next found that identical absorption phenomena 

 are seen in comets long before they reach perihelion. 

 This was a striking result, considering the vast differ- 

 ence in the w^ay in which the phenomena of distant and 

 near meteoric groups are necessarily presented to us ; 

 and bearing in mind that in the case of comets, however 

 it may arise, there is an action which drives the vapours 

 produced by impacts outward from the swarm in a direc- 

 tion opposite to that of the sun. • 



• It must be a very small comet which, when examined 

 spectroscopically in the usual manner, does not in conse- 

 quence of the size of the image on the slit enable us to 

 differentiate between the spectra of the nucleus and en- 

 velopes. The spectrum of the latter is usually so obvious, 

 and the importance of observing it so great, that the 

 details of the continuous spectrum of the nucleus, how- 

 ever bright it may be, are almost overlooked. 



A moment's consideration, however, will show that if 

 the same comet were so far away that its whole image 

 would be reduced to a point on the sHt-plate of the in- 

 strument, the differentiation of the spectra would be lost ; 

 we should have an integrated spectrum in which the 

 brightest edges of the carbon bands, or some of them, 

 would or would not be seen superposed on a continuous 

 spectrum. 



But another revelation still more startling was in store 

 for me, when my assistants and myself had exhausted all 



NO. 1084, VOL. 42] 



the flutings then known to us as origins for the so-called 

 dark bands which remained, and found that none would 

 fit, and we seemed at the end of our tether. 



My ten years' work on carbon made itself quite uncon- 

 sciously felt at this juncture. It suddenly flashed upon 

 me that the 5i7'2, 5167, 516-6, 5167, 5i7"i, &c., recorded 

 by Duner in his observation of a Ononis as the edge of 

 a dark band, could be nothing but the edge of the brightest 

 ba/id of carbon, the bright cometary band par excellence, 

 and therefore that these so-called stars not only resemble 

 comets in their absorption flutings, as we now learn, but 

 in their radiation flutings as well ; in short, these stars 

 were comets, with the difference^a trifling one from my 

 then point of view — that they were not moving round 

 our sun. 



This surmise has since been abundantly confirmed. 

 The dark band of Dundr is a contrast band— the. spectrum 

 looks dark there on account of the extreme brilliancy of 

 the carbon fluting. The other carbon flutings were next 

 sought for and easily found. 



These "stars," then, instead of being like our sun, con- 

 sisted of swarms of meteorites. We have in these bodies 

 a spectrum integrating the radiation of carbon and the 

 absorption of manganese and lead vapour, as in the case 

 of some comets. 



The law of parsimony compels us to ascribe the bright 

 fluting of carbon in these " stars " to the same cause as 

 that at work in comets, where we know it is produced by 

 the vapours between the individual meteorites or repelled 

 from them. Hence we are led to conclude that the ab- 

 sorption phenomena are produced by incandescent vapours 

 surrounding individual meteorites which have been ren- 

 dered intensely hot by collisions, while the carbon light 

 comes from the interspaces. 



I propose in the present paper to give a summary of 

 the evidence of cometary kinship, so to speak, among the 

 other cosmical bodies ; and I shall follow this by an 

 historical statement showing how previous observers 

 have suspected the presence of carbon in " stars." 



First as to cometary kinship. 



The discussion of cometary spectra which I communi- 

 cated to the Royal Society in November 1888 (Roy. Soc. 

 Proc, vol. xlv. pp. 159-217), contained, among other 

 matters, conclusions which have a special bearing on the 

 relations of their spectra to those of other bodies. 



It is obviously desirable to compare this material with 

 the more complete lists of lines which I have now obtained 

 from a very thorough search after all the observations 

 hitherto made of other groups of celestial bodies, since 

 such a comparison — a much more complete one than 

 was possible in the first instance — would strengthen or 

 weaken my hypothesis according as the increased area of 

 observation increased or decreased the number of co- 

 incidences in the spectra of the various groups. 



The more the coincidences are intensified the greater is 

 the probability that comets, nebulas, stars with bright lines, 

 stars with mixed flutings, and the aurora have a common 

 origin, independent of the chemical origins which have 

 been assigned to the various lines by laboratory observa- 

 tions. 



In the tables which follow, the individual observations 

 are not given, but under each heading all the lines or 

 flutings which have been recorded find place. 



I. Comparison of Co7nets and NebulcB. 



We may conveniently begin with a comparison of 

 comets and nebulse. The Great Comet of 1882 and Comet 

 Wells, when near perihelion, are excluded from the list of 

 cometary lines and flutings, as their temperature was too 

 high for fair comparison with most of the nebulae and 

 other low temperature phenomena. 



In cases where any of these higher temperature lines 

 correspond to lines in the comparison spectrum, however, 

 they have been added to the list of cometary lines, in 



