Atmospheric Optical Illusions 95 
visible. Under exceptional conditions halos are observed at 
other angles than 22° and 46° as a result of complicated 
multiple internal reflections in the crystals. 
22° HALO 
REFLECTION ILLUSIONS; TINY MIRRORS IN THE SKY; CROSSES 
The above phenomena are due to the refraction of light in 
ice crystals as has been explained. In the production of opti- 
