,1889.] Variability in condensing Swarms of Meteorites. 42 L 



greatest number of revolving swarms. These will not be the sparsest 

 swarms, for the reason that the short period swarms will only produce 

 a general brightening, as already pointed out, leaving the loDg period 

 swarms predominant. Neither will they be the most condensed, 

 because most of the cometic swarms will sweep clear of the central 

 swarm at periastron passage. They must, therefore, occur in the 

 swarms of mean condensation, if anywhere at all, though mean 

 swarms need not necessarily exhibit irregular variability. The facts 

 observed show that out of the five irregular variables of Group II, 

 three have colours indicating a mean condensation, while two appear 

 to be a little further condensed. 



Irregular Variables. 











B 



a 





Colour. 







o 

















go 





and 



ner, 



6 



a 



a 

 1 



a 



ns 

 o 

 "B 







'8 



o 



,d 

 O 



ft 



ft 





3 



a> 



Chandler. 



Duner. 



m 



18 



1072 



29 



p-Persei 



3-4- 



4-2 





2 



Jr 



8 



37 



2098 



50 



a-Orionis 



1 



1-4 





6 



m 



15 



129 



6181 



196 



o-Herculis 



3-1 



3-9 





5 



»j 



10 



179 



7803 



269 



/x-Cephei 



2-7 



4-8 





6-2 



Rrj 



7 



184 



8273 



281 



^8-Pegasi 



2 2 



2-7 





2 



Jr 



9 



The spectroscopic observations confirm the conclusion that irregu- 

 larity mostly occurs in mean swarms ; it will be seen that with the 

 exception of a Orionis, which is only very slightly variable, the 

 species to which the irregular variables belong are 7—10, indicating 

 mean condensation. 



V. Bright Hydrogen in Variable Stars of Group II. 



I have already pointed out* that in the class of variable stars 

 under consideration the bright lines of hydrogen might be expected 

 to make their appearance at maximum. For since the bodies of 

 Group II are very much akin to nebulae, an increase of temperature 

 such as occurs at maximum should be accompanied by the appearance 

 of bright hydrogen, because a greater quantity of incandescent gas 

 would then occupy the interspaces. 



Under normal conditions there are neither bright nor dark hydrogen 

 lines in the spectra of bodies of Group II, the simple and sufficient 

 explanation being that the bright lines from the interspaces balance 

 the dark lines from the meteoritic nuclei. " Anything which in this 

 condition of light- equilibrium will increase the amount of incan- 

 * Bakerian Lecture, 1888, p. 83. 



