OPTICS 



not appear to form arched bands like the lower colours, 

 but were limited to an elliptical area, as indicated by 

 dotted lines in the diagram. 



On October 2 the blue zone rose to 15° above the 

 horizon, and the purple zone to 25°. 



In all cases the whole arch, from the summit to the 

 horizon, was filled with bands of colour, thereby differing 

 from rainbows and halos. 



Simultaneously with the appearance of a prismatic 

 arch, opposite to the sun there were frequently to be seen, 

 over the sun's position, brilliant sunset colours, which also 

 formed an arch in which the colours were in inverse order 

 to those of the prismatic arch, ranging from orange at 

 the horizon, through yellow and green to blue. The bands 

 were less distinct than in the prismatic arch, but the colours 

 were much brighter. The prismatic arch often occurred 

 without this complementary display being visible. Though 

 not confined to the Antarctic region this phenomenon 

 appears to be exceptionally distinct and frequent there. 



Ice-blink 



The ice-blink of the Great Barrier, viewed from some 

 little distance, was always in the form of a low arch. On 

 January 27 and 28, 1908, we coasted the Barrier all day 

 long, but out of sight of it. All the time the arched ice- 

 blink accompanied us, unvarying except in height as we 

 receded or approached, and apparently always bounded 

 by a true circular arc. When close in to the Barrier the 

 white glare seemed to penetrate to a very limited distance 

 through the air, which was unaffected at a higher level. 



