1888.] 



of the various Species of Heavenly Bodies. 



81 



Zollner in point of fact advances very little beyond the views 

 advocated by Newton and Sir W. Herschel. He considers the main 

 causes of variability to be as follows. He lays the greatest stress upon 

 an advanced stage of cooling, and the consequent formation of scoriae 

 which float about on the molten mass. Those formed at the poles are 

 driven towards the equator by the centrifugal force, and by the 

 increasing rapidity of rotation they are compelled to deviate from 

 their course. These facts, and the meeting which takes place between 

 the molten matter, flowing in an opposite direction, influence the form 

 and position of the cold non-luminous matter, and hence vary the 

 rotational effects, and therefore the luminous or non-luminous appear- 

 ance of the body to distant observers. 



This general theory, however, does not exclude other causes, such as, 

 for instance, the sudden illumination of a star by the heat produced 

 by collision of two dark bodies, variability produced by the revolution 

 of a dark body, or by the passage of the light through nebulous light- 

 absorbing masses. 



; If the views I have put forward are true, the objects now under 

 consideration are those in the heavens which are feast condensed. In 

 this point, then, they differ essentially from all true stars like the 

 sun. 



This fundamental difference of structure should be revealed in the 

 phenomena of variability ; that is to say — The variability of the 

 bodies we are now considering should be different in hind as well as in 

 degree from that observed in some cases in bodies like the sun or 

 <* Lyrae, taken as representing highly condensed types. There is also 

 little doubt I think, that future research will show that when we get 

 short-period variability in bodies like these, we are here really dealing 

 with the variability of a close companion. 



II. On the Variability in Group I. 



That many of the nebulas are variable is well known, though so far 

 as I am aware there are no complete records of the spectroscopic result 

 of the variability. But bearing in mind that in some of these bodies 

 we have the olivine line by itself, and in others, which are usually 

 toighte*f7*~we* have the lines of hydrogen added, it dees not seem 

 unreasonable to suppose that any increase of temperature brought 

 about by the increased number of collisions should add the lines of 

 hydrogen to the spectrum of a nebula in which they were not pre- 

 viously visible." 



exnhmation of the jrydrogen in the variable stars is not at first 

 so envious, but a little consideration will sh6\v that this must happen 

 if my theory be true. 



Since the stars with bright lines are, as I have attempted to show, 



VOL. XLIV. G 



