OPTICS 



remains merely a fine line which cannot be called either 

 lighter or darker than the sky. 



'The figure shows one of the first of these shadows 

 noticed on the western mountains, April 12, 1908. Two 

 bands rose up at different angles. As the sun went round 

 the band on the left became more nearly horizontal, the 

 other went steeper, keeping the same relation to one 



Eakth Shadows, Octobeb 15 



another. The hne on the left could be traced without 

 interruption to the summit of Erebus as shown in the 

 next figure, that on the right died out altogether. The 

 line on the left was curved, but the fact was not remarked 

 upon at the time. 



Shadows from Mount Erebus 



The most remarkable " shadows " were those from 

 Erebus. As early as April 12, 1908, we noticed that the 



3Y9 



