16 



Mr. J. N. Lockyer. On the Classification [Apr. 12, 



them ; the origin of these groups being, first still further condensation, 

 then the condition of maximam temperature, and finally the formation 

 of a photosphere and crust. 



We shall be in a better position to discuss these later stages when 

 the classifications hitherto suggested have been considered. 



Part II. — Classification into Groups. 



, I. Former Classifications of Stars. 



In the various classifications of the celestial bodies which have 

 been attempted from time to time, nebula? and comets have been 

 regarded as things apart from the stars ; but from what I have stated 

 in the first part of this paper, relating to the origin of the various 

 groups of heavenly bodies, it is clear that it is not only unnecessary 

 but unphilosophical to make such a distinction ; and, indeed, if any 

 such separation were needed, such a result would seem to indicate 

 that the line of evolution is by no means so simple and clear as it 

 really seems to be. But although it is no longer necessary to draw 

 this distinction, it is important that I should state the various spectro- 

 scopic classifications which have been attempted in the case of the 

 stars. With this information before us, we shall be better able to 

 see the definite lines on which any new classification must be based to 

 include all celestial forms. 



Fraunliofer, RutJierfurd, and Secchi. 



When we inquire into the various labours upon which our present 

 knowledge of the spectra of the various orders of " stars " is based, 

 the first we come across are those of Fraunhofer, who may be said 

 to have founded this branch of scientific inquiry in the year 

 1814. 



Fraunhofer not only instituted the method of work which now is 

 found to be the most effective, but his observations at that time were 

 so excellent that he had no difficulty in finding coincidences between 

 lines in the spectrum of the sun and of Venus. 



Fraunhofer's reference in his observations runs as follows : — 

 " I have also made several observations on some of the brightest 

 fixed stars. As their light was much fainter than that of Venus, the 

 brightness of their spectrum was consequently still less. I have 

 nevertheless seen, without any illusion, in the spectrum of the light 

 of Sirius, three large lines, which apparently have no resemblance' 

 with those of the sun's light. One of them is in the green, and two 

 in the blue space. Lines are also seen in the spectrum of other fixed 

 stars of the first magnitude ; but these stars appear to be different 

 from one another in relation to these lines. As the object-glass of the 

 telescope of the theodolite has only thirteen lines of aperture, these 



