THE STARS AND NEBULAE 269 



evolution theory, the reader may argue, as indeed Darwin 

 and his adherents do, that since the fission of stars can 

 and does take place, the earth might have flung off the 

 moon. The cases, however, as the sincere reader will 

 see on second thought, are not parallel at all. In this 

 connection compare this interesting passage from Doctor 

 Campbell's book, (p. 291) : 



The two stars [Beta Lyrse] are enormous in size, but of very 

 low density. They are so close together as to be almost in con- 

 tact. The two bodies are in form approximately prolate ellip- 

 soids, with their longer dimensions in the line joining the two 

 bodies. The immediate cause of the variable brightness is due, 

 in large part, to the eclipsing of one body by the other, but there 

 are probably other factors entering to a minor degree, such as 

 tidal ebb and flow, which must exist, as the orbit seems to be 

 slightly eccentric. 



VARIABLE STARS 



In a sense all stars may be said to be Variable, for 

 all alike have explosive graduated shells. In the very 

 large stars, however, the shells are much more homoge- 

 neous and much more fluid, so that the ebullient action is 

 practically uniform. I am speaking now, not of eclipsing 

 variables, whose changeableness is obviously due to the 

 intervention of companion bodies, but of those whose 

 flickering is due to a change that goes on in the star itself. 

 In the previous chapter I have already given the reader 

 my version of the true nature of sun-spots and the rea- 

 sons for their periodicity, and he has only to apply the 

 same principles to the analysis of particular cases and 

 phases of star variation. In this engrossing study, how- 

 ever, two exceedingly important points must be ever 

 borne in mind, namely; (1) that a very high percentage 

 of variables are abnormals, and (2) that abnormal stars 

 are invariably subnormals. By this I mean, that after 

 the collapse of a star, whether by spontaneous eruption 

 or by puncture, it for a time drops to the temperature of 

 stars of lesser mass, and, secondly, that in this collapsed 

 condition it is bound to exhibit changes in its light 

 especially fitful changes. For illustration, compare the 



