OPTICS 



METEOROLOGICAL OPTICS 



Notes by DOUGLAS MAWSON, B.Sc. B.E. 



Mirage. 



Wonderful exhibitions of mirage were of daily occur- 

 rence, especially in the early morning hours. In summer 

 time, travelling over the sea-ice on the Magnetic Pole 

 journej^ it was usually impossible to make theodolite 

 observations between the hours of 1 a.m. and 6 a.m. on 

 account of the extreme distortion of distant objects due 

 to mirage effects. This was attributable to the fact that, 

 at about this hour, a large body of cold dense air descends 

 from the great plateau of South Victoria Land, flowing 

 down the glacier valleys and mingling with the warmer 

 air over the sea-ice. For the same reason the western 

 mountains observed from Cape Royds, always loomed 

 larger in the early morning. Distant capes viewed over 

 the open water often appeared to be hung up in the sky. 



The type of illusion known as Fata Morgana was of 

 very frequent occurrence in the case of distant floating 

 ice rafts; the warmer stratum of the air in proximity to 

 the sea causing the slight irregularities on the ice surface 

 to appear as lofty pinnacles. 



Rings and Crosses Round the Sun and Moon 



These phenomena, proceeding from the refraction of 

 the light of the sun and moon, were numerous and varied. 

 Both large and small rings were observed. Usually only 

 those portions of the ring appeared which neighboured on 

 the horizontal line through the sun or moon, normal to 

 the line of sight. Parhelia and parselene of this kind were 

 of common occurrence. 



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