1888.] of the various Species of Heavenly Bodies. 



13 



The Cometic Nature of Stars with -Bright Lines in their Spectra. 



Seeing that the hypothesis I am working on demands that the 

 luminosity in stars and the bright lines in their spectra are produced 

 by the collisions of meteorites, the spectra of those bodies must in 

 part resemble those of comets, in which bodies by common consent 

 the luminosity is now acknowledged to be produced by collisions of 

 meteorites. 



We must, however, consider the vast difference in the way in which 

 the phenomena of distant and near meteoric groups are necessarily 

 presented to us ; and, further, we must bear 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 direction 

 opposite to that of the sun. 



It must be a very small comet which, when examined spectro- 

 scopically in the usual manner, does not in consequence of the size 

 of the image on the slit enable us to differentiate between the spectra 

 of the nucleus and envelopes. 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, however 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 slit-plate of the instrument, 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. 



The conditions of observation of comets and stars being so different, 

 any comparison is really very difficult ; but the best way of proceeding 

 is to begin with the spectrum of comets, in which, in most cases, for 

 the reason given, the phenomena are much more easily and accurately 

 recorded. 



But even in the nucleus of a comet as in a star it is much more easy 

 to be certain of the existence of bright lines than to record their exact 

 positions,* and as a matter of fact bright lines, including in all pro- 

 bability hydrogen, have been recorded, notably in Comet Wells and 

 in the great comet of 1882. 



The main conclusion to which my researches have led me is that 

 the stars now under consideration are almost identical in constitution 

 with comets between that condition in which, as in those of 1866 and 

 1867, they give us the absolute spectrum of a nebula and that put on 

 by the great comet of 1882. 



* " Observations of Comet III, 1881, June 25. — The spectrum of the nucleus is 

 continuous ; that of the coma shows the usual bands. With a narrow slit there are 

 indications of many lines just beyond the verge of distinct visibility." — Copelaiul. 

 f Copernicus,' vol. 2, p. 226. 



