212 



On the Chemical Constitution of the Stars. 



He showed in the year* 1883 that the total amount of light emitted 

 by a star will, on the nebular hypothesis, first rise and then fall, and 

 he then suggested that the stars of Secchi's Class IY were falling in 

 temperature, while those of Secchi's Class III were rising. This is 

 the same distinction which Lockyer afterwards based on his meteoric 

 theory, and this division is therefore not dependent on the truth of 

 that theory. 



While I think that we shall all admit that different stars are in 

 different stages of development, and that hydrogen stars will 

 ultimately approach more nearly to the state of our sun, it would be 

 unwise to push the argument of uniformity too far, and to say that 

 every star will pass exactly through the same stages. Hitter, who is 

 favourably inclined to the dissociation hypothesis,! gives good reason 

 to believe that the sun's surface was never much hotter than it is 

 now, and that the higher temperature of hydrogen stars is connected 

 with their greater masses. It is, in fact, impossible to admit that the 

 process of development should be quite independent of the total mass 

 of the star. It may be urged that Arcturus must have a mass much 

 larger than that of our sun, and its spectrum, according to Professor 

 Lockyer, is identical with that of the sun. But I suppose that that 

 statement only refers to the blue and violet regiou, for according to 

 Dr. Huggins, to whose early stellar photographs we owe so much, the 

 spectrum of Arcturus in the ultra-violet approaches that of Sirius. 



Further, though I am ready to agree with the general statement 

 that the chemical elements in the stars are the same as those in the 

 sun, and probably in not widely different proportions, I am not con- 

 vinced that the difference in the spectra of stars, which Mr. Lockyer 

 ascribes to ascending and descending temperatures, are not due to a 

 real difference of constitution. 



We have no reason to believe that the nebulae of the present day 

 resemble our sun's ancestor. Some of the stars which are now in an 

 early stage of development may be forming through the condensation 

 of matter which has been left over by others ; and it would not be 

 surprising if the youngest star did not agree in constitution with its 

 aged companions. 



I now pass on to say a few words on Mr. Lockyer's final con- 

 clusions : — Most of us are convinced in our innermost hearts that 

 matter is ultimately of one kind, whatever ideas we may have 

 formed as to the nature of the primordial substance. That opinion 

 is not under discussion. The question is not whether we believe in 

 the unity of matter, but whether a direct proof of it can be derived 

 from the spectroscopic evidence of stars ; for that is what Professor 

 Lockyer claims. It must be observed that even according to him, 



* ' Wied. Annalen,' vol. 20, p. 156. 

 t : Wied. Annalen,' vol. 20, p. 152. 



