554 The Genesis of Double Stars 



his calculations do not enable him actually to draw the state of affairs 

 after the rupture of the neck. 



There are certain difficulties in admitting the exact parallelism 

 between this problem and ours, and thus the final development of 

 our pear-shaped figure and the end of its stability in a form of 

 bifurcation remain hidden from our view, but the successive changes 

 as far as they have been definitely traced are very suggestive in the 

 study of stellar evolution. 



Attempts have been made to attack this problem from the other 

 end. If we begin with a liquid satellite revolving about a liquid 

 planet and proceed backwards in time, we must make the two masses 

 expand so that their density will be diminished. Various figures 

 have been drawn exhibiting the shapes of two masses until their 

 surfaces approach close to one another and even until they just 

 coalesce, but the discussion of their stability is not easy. At present 

 it would seem to be impossible to reach coalescence by any series of 

 stable transformations, and if this is so Professor Jeans's investigation 

 has ceased to be truly analogous to our problem at some undeter- 

 mined stage. However this may be this line of research throws an 

 instructive light on what we may expect to find in the evolution of 

 real stellar systems. 



In the second part of this paper I shall point out the bearing 

 which this investigation of the evolution of an ideal liquid star may 

 have on the genesis of double stars. 



II. 



There are in the heavens many stars which shine with a variable 

 brilliancy. Amongst these there is a class which exhibits special 

 peculiarities ; the members of this class are generally known as Algol 

 Variables, because the variability of the star ^ Persei or Algol was the 

 first of such cases to attract the attention of astronomers, and because 

 it is perhaps still the most remarkable of the whole class. But the 

 circumstances which led to this discovery were so extraordinary that 

 it seems worth while to pause a moment before entering on the 

 subject. 



John Goodricke, a deaf-mute, was born in 1764 ; he was grandson 

 and heir of Sir John Goodricke of Ribston Hall, Yorkshire. In 

 November 1782, he noted tliat the brilliancy of Algol waxed and 

 waned \ and devoted himself to observing it on every fine night from 

 the 28th December 1782 to the 12th May 1783. He communicated 



' It is 8aid that Georg Palitzch, a farmer of Prohlis near Dresden, had about 1758 

 already noted the variability of Algol with the naked eye. Journ. Brit. Astron. Assoc. 

 Vol. XV. (1904—5), p. 203. 



