Atmospheric Optical Illusions 93 
needle-like prisms. The flat flakes, snowflakes, are extremely 
complicated and occur in beautiful patterns,-no two ever 
being exactly alike. With a low power microscope and con- 
siderable care you may be able to collect some snowflakes 
and get a look at them before they melt—but you will have 
to be nimble and resourceful for they have a way of melting 
very quickly. A good suggestion for you, should you ever try 
this, is to cool both the microscope and slides to freezing 
temperature. 
In high clouds water crystallizes into long thin six-sided 
needles either with flat ends or, more rarely, with sharp py- 
ramidal points. 
SUNDOG o> SUNDOG 
wbly 
wosse 
~ suewr” za 
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; = 
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HORIZON 
GHOST SUNS, ARCS OF LOWITZ 
When the light of the sun falls upon ice crystals suspended 
in the air it produces striking effects. The crystals act as tiny 
prisms. Since they are falling uniformly through the air they 
tend to get lined up in one direction with their sides vertical. 
The sides are inclined to one another at 60°, but the ends are 
inclined to the sides at 90°. Hence the crystals may act in a 
variety of ways, either as 60° or 90° prisms, as combinations, 
