1888.] 



of the various Species of Heavenly Bodies. 



25 



from most stars by the fact that we get evidence of radiation alone, 

 or almost alone so far as we know. Absorption has been snspected in 

 the spectra of some nebulae,* and has been observed beyond all doubt 

 in some comets. f But there are some stars in which we also get 

 radiation, accompanied by certain absorption phenomena. But there 

 is no difficulty in showing that nebulas and comets are more special 

 on account of their bright lines than on account of their absorption 

 bands. I have already shown that in all probability the stars with 

 bright lines are most closely allied with nebulae. Indeed, it seems as 

 if they are very nearly akin to those condensations in nebulae, showing 

 an undoubted olivine and hydrogen spectrum, which gave them the 

 appearance of resolvability. It seems, also, highly probable that 

 future observations with instruments of great light-collecting power, 

 will show that in nebulae, the spectra of which are recorded as 

 continuous, lines including the remnants of some of the carbon 

 flutings, which there is good reason to believe have already been 

 traced in the spectra of bright line stars, are also present. From this 

 point of view, the various recorded observations of regions of different 

 colour in certain nebulae acquire an additional interest. It is also 

 clear that since the only real difference between comets and other 

 meteor swarms of equal denseness is that the former are in motion 

 round the centre of our system, comets whether at aphelion or at 

 perihelion will fall into this group. We may, therefore, form the first 

 group of bodies which are distinguished by the presence of bright 

 lines or flutings in the spectrum. 



The great distinction between the first group and the second would 

 be that evidences of absorption now become prominent, and side by 

 side with the bright flutings of carbon and occasionally the lines of 

 hydrogen we have well-developed fluting absorption. 



The second group, therefore, is distinguished from the first by 

 mixed flutings as well as lines in the spectrum. 



* " Nebula [No. 117, 51 h. 32 M. R.A. Oh. 35 m. 5 3 s. ; N.P.D. 49° 54/ 12'7". 

 Very, very Wght; large, round; pretty suddenly much brighter in the middle]. — 

 This small but bright companion of the great nebula in Andromeda presents a 

 spectrum exactly similar to that of 31 M. [the great nebula in Andromeda]. The 

 spectrum appears to end abruptly in the orange ; and throughout its length is not 

 uniform, but is evidently crossed either by lines of absorption or by bright lines." — 

 (Huggins, 'Phil. Trans.,' vol. 154, p. 441.) 



f "A dark band was noticed at wave-length 5679." — (Copeland, "Comet III? 

 1881," ' Copernicus,' vol. 2, p. 226.) 



" May 20. — With none of these dispersions could any bright band's, properly so- 

 called, be distinguished ; but two faint broad dark bands, or what gave that 

 impression, crossed the spectrum. ... A third dark band was suspected near 

 D on the blue side of that line." — (Maunder, " Comet a, 1882 (Wells)," ' Greenwich 

 Spectroscopic Observations,' 1882, p. 34.) 



" The dark bands were observed again, and their wave-lengths measured on 

 May 31."— (Ibid., p. 35.) 



