1888.] of the various Species of Heavenly Bodies. 21 



Class I. Spectra in which the Metallic Lines are extremely Faint or 

 entirely Invisible. — The most refrangible parts, blue and violet, are 

 very vivid. The stars are white. 



(a.) Spectra in which the lines of hydrogen are very strong. 



(&.) Spectra in which the lines of hydrogen are wanting. 



(c.) Spectra in which the lines of hydrogen and D 3 are bright. 



Class II. Spectra in which the Metallic Lines are Numerous and very 

 Visible. — The blue and violet are relatively weaker ; in the red part 

 there are sometimes faint bands. The colour of the star is clear 

 bluish- white to deep reddish-yellow. 



(a.) Spectra with numerous metallic lines, especially in the yellow 

 and green. The lines of hydrogen are generally strong, but never as 

 strong as in the stars of Class I. In some stars they are invisible, 

 and then faint bands are generally seen in the red formed by very 

 close lines. 



(6.) Spectra in which besides dark lines and isolated bands there are 

 several bright lines. 



Class III. Spectra in which besides the Metallic Lines there are 

 numerous Lark Bands in all parts of the Spectrum, and the Blue and 

 Violet are remarkably Faint. — The stars are orange or red. 



(a.) The dark bands are fainter towards the red. 



(6.) The bands are very wide, and the principal are fainter towards 

 the violet. 



It is pointed out that if this classification be true, there must be 

 links between all the classes given. Now it is perfectly obvious that 

 if this classification includes in its view all the stars, and if there is 

 a line of ascending as well as descending temperatures — that is to say, 

 if some of the stars are increasing their temperatures, while others 

 are diminishing them — the classification must give way. 



It is not difficult to see, in the light of my communication to 

 the Society of November 17th, that it has given way altogether, and 

 principally on this wise. 



The idea which underlies the classification is that a star of Class I 

 on cooling becomes a star of Class II, and that a star of Class II has 

 as it were a choice before it of passing to Class Ilia or Class III6. 

 Thus under certain conditions its spectrum will take on the appear- 

 ance of Secchi's third type, Class Ilia- (Yogel) ; on certain 

 other conditions it will take on the appearance of Secchi's fourth 

 type, Class III6 (Vogel). There is now, however, no doubt what- 

 ever that Secchi's Class Ilia represents stars in which the tem- 

 perature is increasing, and with conditions not unlike those of the 

 nebulas — that is to say, the meteorites are discrete, and are on their 

 way to form bodies of Class II and Class I by the ultimate vaporisa- 

 tion of all their meteoric constituents, There is also no doubt that the 

 stars included in Class III6 have had their day ; that their tempera- 



