92 



On the Classification of Heavenly Bodies. [Apr. 12, 



[Received April 9, 1888J. 



Conclusion. 



Although in this paper I have chiefly confined myself to the discus- 

 sion of the probable uature of the bodies in Groups I and II, I have 

 also been engaged in the investigation of the spectra of some of the 

 bodies included in the remaining groups, with a view to their detailed 

 classification. Here, however, the work goes on slowly for lack of 

 published material, especially with regard to the examination of the 

 stars which should be included in Groups III and V. With regard to 

 Group VI, however, I may state that all the stars the spectra of which 

 have been recorded have been distributed among five well-marked 

 species, and that there is evidence that some of the absorption is pro- 

 duced by substances which remain in the atmosphere during the next 

 stage, that of Group VII. This probability is based, upon the fact 

 that some of the bands are apparently coincident with bands in the 

 telluric spectrum as mapped by Brewster, Angstrom, Smyth, and 

 others. 



In special connexion with the discussion of Groups I and II, the 

 spectrum of the Aurora Borealis, concerning which I have already 

 (January 19, 1888) communicated to the Society a preliminary note 

 indicating the possible connexion between the spectra of the aurora 

 and of stars of Group II, has been further studied. By this inquiry 

 the work has been advanced a stage, and the view is strengthened 

 that in the case of the aurora the spectrum is mainly one of metallic 

 nutings and lines, probably produced by electric glows in an atmo- 

 sphere charged with meteoric dust and the debris of shooting stars ; 

 while in bodies of Groups I and II it is chiefly produced by collisions 

 between the component meteorites. 



It may be thought by some premature to give an extended discus- 

 sion of the bodies belonging to the two groups which have been dealt 

 with before my view of their constitution has been thoroughly tested 

 by observations. My reasons, however, for the present publication 

 are twofold. I have not sufficient optical power at my disposal to go 

 over the ground myself, and I have been anxious to save time by 

 indicating to those who are at present occupied with stellar spectra, 

 or who may be prepared to undertake such observations with suffi- 

 cient optical appliances, the points chiefly' requiring investigation as 

 being of a crucial nature. 



From this point of view the small number of observatories paying 

 attention to these matters is much to be regretted, and the import- 

 ance of Mrs. Draper's noble endowment of spectroscopic photography 

 at Harvard Collegj will be best appreciated, 



I may, however, say that I have made some observations in the 



