45 



CHAP. V. STELLAR ATMOSPHERES. 



AFTER the laboratory work undertaken with the view of att3mpting to 

 find explanations of the various phenomena presented by the sun had 

 reached a certain stage, it became necessary to endeavour to get an 

 idea of the sun's place among the stars by a discussion of all I/he 

 existing spectroscopic observations which might throw light upon the 

 subject. 



At that time a very large number of the most important lines, 

 both bright and dark, recorded in stellar spectra were of unknown 

 origin. The inquiry, therefore, in the case of all the hotter stars had 

 to do with the spectral lines as hieroglyphics, not as special chemical 

 representatives. 



When I began the inquiry, the prevailing ideas were that the first 

 period of a star's life was one of the highest temperature, and that all 

 the differences observed were due to different stages of cooling having 

 been reached. With regard to the nebulae, they, it was imagined, 

 formed a different order of created things from the stars. 



Passing over the old views, among them one that the nebulae were 

 holes in something dark, which enabled us to see something bright 

 beyond ; and another that they were composed of a fiery fluid, I may 

 say that not long ago they were supposed to be masses of gases only, 

 existing at a very high temperature ; and it was also suggested that 

 they, perchance, represented the residua in space left after all the stars 

 had been formed. 



The upshot of this inquiry forms the subject matter of two com- 

 panion volumes,* so I need not dwell upon it in any detail here. But 

 it is necessary that I should state, as briefly as may ba, the results to 

 which the discussion of all the then available spectroscopic observations 

 led me. 



All the observations were satisfied by the working hypothesis of 

 the evolution of all cosmical bodies from meteorites, the various stages 

 recorded by the spectra being brought about by the various conditions 

 which follow from the hypothesis. 



The nebulas present us with the first stage. They are taken to be 

 sparse swarms of meteorites colliding together, and thus producing 

 their luminosity, which spectroscopically is found to be due to permanent 



* The Meteoritic Hypothesis and The Sun's Place in Natiire. Maemillan. 



