18 



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



line spectra and the third and fonrth had fluted ones. At that time 

 the important distinction to be drawn between line- and fluted-spectra 

 was not so well recognised as it is at present ; and further the relation 

 of spectra to temperature was not so fully considered. Secchi, as a 

 result of laboratory work, however, at once showed an undoubted 

 connexion between the absorption flutings in the stars of the fourth 

 type and the bright ones seen in the spectrum or carbon under certain 

 conditions ; and although this conclusion has been denied, it has since 

 been abundantly confirmed by Vogel and others (see Yogel, 6 Publica- 

 tionen, &c, Potsdam,' No. 14, 1884, p. 31). 



Relation to Temperature. 



At the time that Secchi was thus classifying the stars, the question 

 was taken up also by Zollner, who in 1865 first threw out the sugges- 

 tion that the spectra might probably enable us to determine some- 

 what as to the relative ages of these bodies ; and he suggested that 

 the yellow and red light of certain stars were indications of a reduc- 

 tion of temperature (Zollner, ' Photometrische TJntersuchungen,' 

 p. 243). 



In 1868 this subject occupied the attention of Angstrom with 

 special reference to the contrasted spectra of lines and flutings. On 

 this he wrote as follows, showing that temperature considerations 

 might help us in the matter of variable stars (' Recherches sur le 

 Spectre solaire,' Upsala, 1868) : — 



''D'apres les observations faites par MM. Secchi et Huggins, les 

 raies d'absorption dans les spectres stellaires sont cle deux especes : 

 chez l'une, le spectre est raye de lignes tres-fines, comme le spectre 

 solaire ; chez l'autre, les raies constituent des groupes entiers a espaces 

 egaux ou des bandes nuancees. Ces derniers groupes appartiennent 

 vraisemblablement aux corps composes, et je mentionnerai, en par- 

 ticulier, que ceux trouves dans le spectre de a, Orionis ressembient 

 fort aux bandes lumineuses que donne le spectre de l'oxyde de man- 

 ganese. Suppose que ma theorie soit juste, l'apparition de ces bandes 

 doit done indiquer que la temperature de l'etoile est devenue assez 

 basse pour que de telles combinaisons chimiques puissent se former 

 et se conserver. 



" Entre ces deux limites de temperature chez les etoiles, limites que 

 Ton peut caracteriser par la presence de l'une ou de l'autre espece 

 des raies d'absorption, on peut s'imaginer aussi un etat intermediaire, 

 dans lequel les gaz composes peuvent se former ou se dissocier, suivant 

 les variations de temperature auxquelles ils sont assujettis par Taction 

 chimique nieme. Dans cette classe doivent probablement etre com- 

 prises les etoiles dont l'intensite de lnmiere varie plus ou moins 

 rapidement, et avec une periodicite* plus ou moins constante." 



In the year ld/3, I referred to this subject in my Bakerian Lecture 



