OPTICS 



central tract of deep clear blue, which looks exactly like 

 a bit of ordinary blue sky, seen through a gap in the 

 cloud. A great bank of grey stratus passing behind the 

 wisps of illuminated cloud, proved that there was no blue 

 sky present. 



The colours of the iridescent clouds were brighter than 

 in any of the other phenomena of the same class, such 

 as the prismatic sunrises and sunsets. They were brighter 

 than any rainbow and only to be compared with the 

 spectrum of sunlight shown by a glass prism. 



Ieidescent Clouds, August 22 



Earth Shadows 



The name is that used by Captain Scott, though per- 

 haps their appearance may be better suggested if they 

 were called aerial shadows. These shadows appear to be 

 generally from mountain peaks, but their source is often 

 hidden. They most commonly take the form of straight 



3.77 



