82 



Mr. J. N. Lockyer. On the Classification [Apr. 12, 



very akin to nebulae in their structure, we might, reasoning by analogr, 

 suppose that any marked variability in their case also would be 

 accompanied by the coming out of the bright hydrogen lines. 



This is really exactly what happens both in /3 Lyra? and in 7 Cas- 

 siopeias. In (3 Lyras the appearance of the lines of hydrogen has a 

 period of between six and seven days, and in 7 Cassiopeiae they appear 

 from time to time, although the period has not yet been determined. 



III. Ox the Variability ix Geoup II. 



This same kind of variability takes place in stars with the bright 

 fiutings of carbon indicated in their spectra, o Ceti being a marvellous 



Fig. 17. — Explanation of the variability of bodies of Group II. (1.) Maximum 

 variation. The ellipse represents the orbit of the smaller swarm, -which revolves 

 round the larger. The orbit of the revolving swarm is very elliptical, so that 

 at periastron the number of collisions is enormously increased. 



case in point. In x Orionis, one of the most highly developed of 

 these stars, the hydrogen lines are invisible ; the simple and sufficient 

 explanation of this being that, as I have already suggested, the bright 

 lines from the interspaces now at their minimum and containing 



