THE LIGHT OF THE STABS. 187 



the maxima are at times retarded and at others 

 accelerated with no apparent law. The spectro- 

 scopic investigations of Campbell in 1898 have 

 shown that Mira Ceti is a solitary star, while 

 bright lines of hydrogen appear in its spectrum 

 at maximum, showing that the variations are 

 due to periodical conflagrations in its atmo- 

 spheres. In many other long - period variables 

 bright lines have been observed. 



A remarkable fact regarding these stars is the 

 amount of their light change. Mira Ceti, for 

 instance, varies from the first to the ninth 

 magnitude, and U Orionis from the sixth to 

 the twelfth. As M. Flammarion says, "the 

 longer the period the greater the variation." 

 Another remarkable fact is that their light 

 curves show a curious resemblance to the curves 

 of the solar spots, only on a vastly greater scale, 

 which indicates that, relatively, these long-period 

 variables are much older than our Sun, the small 

 variations in the light of which are imperceptible. 

 "Here, if anywhere," says Miss Clerke, "will be 

 found the secret of stellar variability." 



To the irregular variables no period can be 

 assigned. Betelgeux, in Orion, the variation of 

 which was noted by Sir John Herschel in 1840, 

 is a typically irregular variable. But the most 

 extraordinary of all variables is 77 Argus, in 



