PLATE XI. 



Low-level photograph, showing the dense calcium vapor lying just above the 

 photosphere. In this photograph very little of the penumbra is coverett by the 

 calcium vapor, but evidences may Ite seen, especially in the southern part of the 

 penumbra of the largest spot, of the columns of vapor which are greatly devel- 

 oped at the higher levels. 



156 



