The results of various 
experiments using this 
apparatus and method suggest 
that the moon illusion is 
created just as the taking-into-
account theory predicts: The 
apparent size of the moon is 
computed from its perceived 
distance; as its apparent 
distance increases, its size is 
perceived to grow. It was shown 
that, when a scene was used 
that permitted a greater 
apparent distance to the 
horizon or when cloud cover 
was present that added a 
"ceiling" to the sky in addition 
to the "floor" ordinarily 
provided by the terrain, for 
example, the moon illusion 
increased. Under such 
conditions, the magnitude of 
the illusion, expressed as a 
ratio of the perceived size of 
the horizon moon to the 
elevated moon, was 
approximately 1.5 to 1.