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. 
Il. 
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 that 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 
1 It is said 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. 
