The St Louis Arch

st louis arch

Probably the largest 'real' optical illusion in the world is the St Louis arch above. Contrary to (very persistent perception) the arch is exactly as wide as it is tall. This classic optical illusion is due to our eyes automatically heightening a shape that points upwards and thins as it rises. You can check that the two yellow lines below have identical length.

st louis arch 2

Norman Fenton

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