The Piscian Stars. 



131 



Number of zones. 



Magnitudes of stars in 

 which they are seen. 



4. 



5 -5—8 2 



3 



6 -0—9 -5 



2 



8 -0—9 -0 



Here, again, the visibility of the zones does not depend altogether 

 upon the magnitude. There are stars as bright as the sixth magni- 

 tude which only give three zones, whilst some as low as 8-2 give four. 

 Duner refers to this difference as follows : — 



"Puis I'intensite de la luraiere des zones brillantes peut varier 

 considerablement chez les etoiles de la meme grandeur. Dans les 

 etoiles d'un rouge fonce, la zone ultra-bleue est extremement faible en 

 comparaison avec la meme zone dans les etoiles rouge jaune ; et chez 

 les etoiles faibles, cette zone est tout-a-fait invisible, et meme la zone 

 bleue est tres difficile a voir si elles sont tres rouge. ""^ 



Another important difference is the variation in the intensity of the 

 citron band of carbon (band 6) as compared with the other bands. 

 Duner also refers to this point (p. 10) as follows : — " Mais aussi la 

 bande principale a la longueur d'onde 563 est d'une opacite tres variee. 

 Chez certaines etoiles, elle est presque aussi foncee que les deux 

 autres bandes principales ; mais dans certains spectres elle est assez 

 faible, et semble, probablement a cause de cela, etre beaucoup moins 

 large que les bandes aux longueurs d'onde 516 et 473. Celles-ci, et 

 surtout la premiere d'entre elles, sont toujours tres fortes et tres 

 larges, et forment le caractere le plus prononce de ces spectres." A 

 discussion of the observations shows that this variation is independent 

 of the magnitudes of the stars. 



Thus we find that the band is dark in some stars with magnitudes 

 varying from 5*4 to 8-0. It is interesting to note that this band, as I 

 have shown, is also the one most subject to variations in the spectra 

 of comets, t 



It thus appears that there are distinct differences in the spectra, 

 quite independent of the difficulties in recording the details. 



It will be clear that the stars with the longest spectra, characterised 

 by four " zones," must be placed above those with shorter spectra on 

 the temperature curve. As none of the stars, however, show more 

 than four zones and only one less than three, this alone does not dis- 

 criminate sufficiently between the different species, and we have there- 

 fore to look to the variations in the carbon flutings and secondary 

 bands for finer sub-division. 



* ' Sur les Etoiles,' &c., p. 9. 



t ' Roy. Soc. Proc.,' vol. 45 (1889), p. 168. 



