152 PROF. A. FOWLER, F.R.S., ON THE SPECTRA OF STARS AND NEBULffi. 



The generally accepted view that the ancestors of stars are 

 represented by nebulae requires that these bodies should 

 contain all the materials of which stars are known to be com- 

 posed. But the nebulae have a very simple spectrum of bright 

 lines, among which only those belonging to hydrogen and 

 helium have been certainly identified. Hence the modern view, 

 ably supported by the mathematical investigations of Professor 

 Nicholson, that nebulae consist largely of atoms of very 

 primitive forms of matter, and that the stellar sequence may 

 possibly indicate the order of evolution of the chemical 

 elements as well as that of the stars themselves. However 

 that may be, observations lately made at the Lick Observatory 

 have shown a direct relation between the spectra of nebulas 

 and the Wolf-Rayet stars of Class 0, which stand at the 

 head of the stellar sequence and thus mark the first stage in the 

 condensation of nebulae. That nebulae must contain matter 

 other than that indicated by their spectral lines is also strongly 

 suggested by observations of " new stars," which at one stage 

 show lines of iron and other known elements, and at a later 

 stage exhibit the lines characteristic of nebulae. 



Further investigations in many directions are still needed to 

 complete the story, but all modern work tends to strengthen 

 our belief in the chemical unity of the universe, and in an 

 evolutionary development of stars from the primitive conditions 

 represented by nebulae. 



A full report of Professor Fowler's lecture and of the discussion 

 following it will be published in Volume XLVIII of the Journal of 

 Transactions of the Institute. 



