132 INORGANIC EVOLUTION. [CHAP. 



Bright-line Stars. 



These, then, are the results with regard to the stars having obviously 

 dark lines in their spectra, but besides these there are many so-called 

 bright-line stars. 



I should say that there has necessarily been a change of front in our 

 views with regard to these bright-line stars since they were first classi- 

 fied with nebulae. The nebulae are separated generic-ally from the stars 

 by the fact that in their case we have to deal with bright lines, that is 

 to say, we deal only with radiation phenomena, and not with absorp- 

 tion phenomena, as in the case of the stars so far considered ; and in 

 the first instance it was imagined that the bright-line stars were, from 

 the chemical point of view, practically nebulae, although they appeared 

 as stars, because the brightest condensations of them were so limited 

 or so far away that they gave a star-like appearance in the telescope. 



Since that first grouping of bright-line stars, by the work chiefly of 

 the American astronomers, it has been found that in a large number 

 of cases they hove also dark lines in their spectra, and that being so we 

 must classify them by their dark lines instead of by their bright ones ; 

 and the bright-line stars thus considered chiefly turn out to be gaseous 

 stars, with a difference. What is that difference 1 It is this, I think: 

 in the case of the bright-line stars we are dealing with the condensa- 

 tions of the most disturbed nebulae in the heavens, together with the 

 light which we get from the nucleus of that nebula which appears as a 

 star, and can be spectroscopically classified with the other dark-line 

 stars, inasmuch as the surrounding vapours close to the star produce 

 absorption, and therefore give us dark lines ; other parts of the nebulae, 

 probably those further afield, give us bright lines which mix with the 

 dark ones. Therefore we get both bright lines and dark lines under 

 these conditions. So far as the result goes up to the present moment, 

 it looks as if we have now to consider that these bright-line stars, instead 

 of being nebula? merely, are gaseous stars at a very high temperature, 

 in consequence of the fact that the nebula which is surrounding them, 

 which is falling upon them, is increasing the temperature of the central 

 mass by the change of vis vim into heat. Pickering,* in his discussion 

 of these stars, had thirty-three to deal with, and he found that there 

 was a wonderful tendency among these to group themselves along the 

 Milky Way : that very few of them, in fact, lay outside its central 

 plane ; the galactic latitude, the distance in degrees from the plane 

 being limited in the generality to only 2, and the greatest departure, 

 the greatest galactic latitude, was something within 9. That was the 

 story in 1891. Two years afterwards Campbell, another distinguished 



* Astr. Nach., No. 2025. 



