82 LIGHT SCIENCE FOR LEISURE HOURS. 



part of a second of arc, so that no less than twenty-six 

 such distances could be placed between the components 

 of that well-known test- object, the double companion 

 of the star Gamma Andromedse.* 



Next below this coloured envelope there is the 

 mottled photosphere, either a white-hot surface with 

 relatively dark pores all over it, or, according to other 

 and better authorities, a surface of white-hot spots 

 spread over a relatively dark background. Here we 

 are describing merely its appearance; what the con- 

 stitution of this surface may in reality be remains yet 

 to be determined. 



Beneath the photosphere there are vast depths of 

 vapour, for when the photosphere is broken through 

 where spots are formed, the spectroscope tells us that 

 the relatively dark regions thus disclosed are filled 

 with the vapours of various elements. We know that 

 the dark lines which cross the rainbow-tinted solar 

 spectrum are caused by the light-absorbing action of 

 the vapours which surround the sun, and these lines 

 are seen more distinctly in the spectrum of a sun-spot 

 than in that of the photosphere. 



Now it is worthy of notice that all that has thus far 

 been discovered tends to confirm the theory put for- 



* The view here presented was completely confirmed during the 

 eclipse of last December. Professor Young and Mr. Pye independently 

 recognised a layer whose spectrum showed all the Fraunhofer lines 

 reversed. By observing at the place where the moon had just concealed 

 the last fine sickle of the solar disc, they obviated the effects of diffrac- 

 tion, which render the observation wholly impossible in the case of the 

 uneclipsed sun. 



