1889.] of the various Species of Heavenly Bodies. 215 



In each case, an increase in temperature is accompanied by the 

 addition of continuous spectrum. 



Further condensation of the nebulous swarm results in an apparent 

 star with a spectrum consisting of bright flutings and lines in 

 addition to continuous spectrum, and this condition, we have seen, 

 also has a parallel in cometary spectra. 



Still further condensation of the nebulous swarm results in a body 

 of Group IT, giving the radiation of carbon and metallic fluting 

 absorption. It has been seen that this is also reproduced in cometary 

 spectra. 



The next stage in the history of a nebulous swarm is the forma- 

 tion of a body of Group III, in which the carbon radiation has 

 disappeared, and the metallic flating- has given way to line-absorption. 

 This, we have seen, was exactly reproduced in the Great Comet of 

 L882, and in Comet 6, 1881, to which reference has just been made. 

 In the former case, both radiation and. absorption lines were recorded, 

 this being due to the repellent action of the sun, as already explained. 



The general sequence of phenomena, both in nebulous swarms and 

 comets, may be stated as follows : 



Magnesium (500) radiation. 

 Carbon and manganese fluting radiation. 

 Manganese and lead fluting absorption. 

 Line radiation and absorption. 



It is now universally agreed that comets are swarms of meteorites, 

 and hence this connexion between comets and bodies of Groups I, 

 II, and III strengthens the general view, which would have been 

 worthless had the cometary spectra been otherwise. We have, there- 

 fore, well-marked species of swarms revolving round the sun exhi- 

 biting just the same series of phenomena as marked species of non- 

 revolviiig ones in space. 



Schiaparelli's view, therefore, that comets consist of materials 

 similar in nature to that of which the nebulae are composed drawn 

 into the solar system by solar attraction, is now abundantly demon- 

 strated by the spectroscopic survey of nebulae, stars, and comets 

 detailed in my previous papers and in the present one. 



[Note. December 4^/t. Since the above was written, my assistants 

 have made some observations of the nebula in Andromeda, which 

 were suggested by the foregoing discussion. We have seen that 

 some planetary nebulae give the same spectrum as a comet at 

 aphelion. It appeared that if the nebula of Andromeda .were further 

 advanced than a planetary nebula in condensation, it should give a 

 spectrum approximating to one of the more advanced cometary stages 

 which have been already discussed. 



