34 Variable Stars . [January, 
the whole period occupying some 70 hours in its com- 
pletion. 
Several theories have been put forward to account for the 
strange phenomena which this star exhibits, but hitherto, as 
it seems, without much success. We shall examine them 
one by one, although some of them will not call for more 
than a cursory notice. 
We may rejedt at the outset the supposition that Algol is 
of an irregular shape, and therefore presents, in consequence 
of his rotation, some parts of his surface at an ever-varying 
angle to the earth, the brilliancy being greatest when the 
greater portion of the surface is square to the line of sight. 
And the same reasons which enable us to rejedt this, enable 
us also to cast aside the idea that one side of Algol is 
brighter than the other. For it must be abundantly clear 
that if we suppose Algol to be in a sun-like condition, he 
must be surrounded — as other suns are — by an elastic 
gaseous envelope possessing light and heat-giving properties. 
It follows, then, that in the first case the tendency of these 
clouds would be to spread themselves over, and obliterate 
from sight the irregularities upon the surface of this star ; 
whilst, in the second place, it must be regarded as next to 
impossible that one portion of a star’s surface should be in 
a different condition to another, and remain so for a very 
long period. In all questions such as this analogy is our 
safest guide ; and if we look upon Algol as a sun like our 
own, we must rather infer that the mighty forces which are 
necessarily in ceaseless adtion throughout his whole globe 
would tend to fully equalise the light and heat-giving power 
of his whole surface. Moreover, Prof. Young has indicated 
reasons for the conclusion that the sun’s nucleus is not solid, 
but that, in all probability, it is in a nebulous state through- 
out, — a consideration which if admitted would, obviously, 
completely negative, upon analytical grounds, either of the 
above theories. 
I pass, also, the sun-spot theory — the theory, namely, that 
sun-spots of large dimensions check the emission of light 
from the surfaces of the different variable stars, the observed 
effedt being caused by the star’s motion of rotation. So far 
as Algol alone (or indeed any other star whose maxima and 
minima of brightness occur with an unbroken regularity) is 
concerned, a theory such as this is but the re-statement, in 
a slightly modified form, of the theory that one side of Algol 
is brighter than the other. We have yet to learn that any 
disruption on the surface of our own sun could last un- 
changed for a very long period. 
