Atmospheric Optical Illusions 97 
sun. Sundogs produced by reflection of sunlight from sus- 
pended ice spicules are pure white; those produced by re- 
fraction are somewhat colored. Other reflection phenomena 
include’ huge pillars passing vertically through the sun, or 
very rarely bright white crosses with center at the sun or 
moon. These crosses are supposed to be the natural explana- 
tion of the ones seen during such manifestations as those 
mentioned at the beginning of this chapter. One more cross 
story: British troops at the battle of the Somme in World 
War I swore that they saw a cross in the heavens. It is sup- 
posed to have happened at night after hours of an overcast 
cloudy sky. Suddenly the moonlight broke through the 
clouds in the form of a perfect cross—a perfect setup for a 
reflection illusion by little ice mirrors too. 
CORONAS, WEATHER PROPHETS 
Diffraction phenomena of the atmosphere are caused by 
