1904.] On the Temperature Classification of Stars. 



227 



a solid is determined by the nature of the atoms composing the 

 physical molecules, and is not a measure of the thermal work done in 

 expansion. 



The paper concludes with a discussion of tbe relations of specific 

 heat to atomic weight in the solid, liquid and gaseous states. 



<£ Further Eesearches on the Temperature Classification of Stars." 

 By Sir Noeman Lockyee, K.C.B., LL.D., F.B.S. Beceived 

 January 30, — Bead February 18, 1904. 



[Plates 7—9.] 

 Contents. 



page 



1. Historical Review 227 



2. Aims and Conditions of the present Research 229 



3. The Observational Conditions 230 



4. Description of the Instrument used 231 



5. Method of Work 231 



6. Description of the Photographs 233 



7. Discussion of the Photographs 235 



8. Conclusions 237 



9. Description of Plates ... 238 



1. Historical Bemeiv. 



In my first Bakerian Lecture in 1873 I dealt with the question of 

 the spectra of stars, and pointed out that the facts accumulated up to 

 that time by Butherford and others led to the view that in the 

 reversing layers of the sun and stars various degrees of dissociation are 

 at work. 



I also suggested that the stellar evidence indicated that one of the 

 results of dissociation temperatures could be to " prevent the coming 

 together of atoms which at the temperature of the earth, and at all 

 artificial temperatures yet obtained here, compose the metals, the 

 metalloids, and compounds."* 



In a subsequent communication to the Paris Academy I wrote,! 

 I II semble que plus une etoile est chaude plus son spectre est simple, 

 et que les elements metalliques se font voir dans l'ordre de leurs poids 

 atomiques." 



This last generalisation rested upon the great preponderance of 

 hydrogen in certain stars, which I classed as hottest on the ground that 

 the blue end of the spectrum was open. Of the spectrum of helium, 



* ' Phil. Trans.,' vol. 164, p. 479. 



f ' Comptes Rendus,' vol. 77, 1873, p. 1357. 



