You know that in an atmosphere of uniform density the most distant things seen through it, such as the mountains, in consequence of the great quantit… - Leonardo da Vinci

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You know that in an atmosphere of uniform density the most distant things seen through it, such as the mountains, in consequence of the great quantity of atmosphere which is between your eye and them, will appear blue. Therfore you should make the building... wall which is more distant less defined and bluer. ...five times as far away make five times as blue.