84 



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



The first test we have of the theory is that there should be more 

 variability in this group than in any of the others. Others are as 

 follows : (2) When the swarm is most spaced, we shall have the least 

 results from collisions, but (3) when it is fairly condensed, the effect 

 at periastron passage (if we take the simplest case of a double star in 

 posse) will be greatest of all, because (4) condensation may ultimately 

 bring the central swarm almost entirely within the orbit of the 

 secondary (cometic) body, in which case no collisions could happen. 



Fig. 19. — Explanation of the variability of bodies of Group IT. (3.) Minimum 

 variation. Under the conditions shown, the smaller swarm will never be 

 entirely out of the larger one, and at periastron the number of collisions will 

 not be very greatly increased. Consequently, the variation in the amount of 

 light given out' will be small. 



In the light , of what has gone before it is as easy to test these 

 points as the former ones. 



The Frequent Occurrence of Variability in Group II. 



The total number of stars included in Argelander's Catalogue, 

 which deals generally with stars down to the ninth magnitude, but in 



