In 1506, Leonardo da Vinci completed his portrait of Madonna Lisa, Neapolitan wife of one Zanobi del Gioconda. The face and smile of this placid lady exhibited a haunting, enigmatic charm, and it is said that Leonardo arranged for music to be played during the sittings so her countenance might retain its rapt demeanour. The picture is celebrated for its subtlety of expression, the precision of its drawing, and for the romantic nature of its background.
But in meteorological circles, Leonardo's Mona Lisa is noted for another reason: it is allegedly the first Renaissance painting in which the sky is hazy. Artworks theretofore had portrayed the sky with perfect visibility, but the steep mountains of the Mona Lisa, , with their strange perspectives and mysterious waterways, are viewed through a misty or hazy atmosphere, which adds a luminous quality to the painting.
There seems little doubt that Leonardo's haze is a deliberate device intended to enhance the effect. On the other hand, it seems reasonable to suppose that, in general, artists over the centuries painted what they saw. Some years ago, it occurred to an American professor to estimate the visibility portrayed in some 7,000 paintings, completed between 1400 and 1970, to see if they would tell us anything about the prevailing clarity of the atmosphere in days gone by.
His first step was to see if the theory might be plausible. He did this by analysing paintings from selected regions of the western world from 1850 to the present, and comparing the results with meteorological observations for the areas in question. Not surprisingly, he found that clearest atmospheres were painted by the Mediterranean schools, while the haziest air is found in British pictures. More importantly, he found that average visibilities depicted by the artists compared very well with average observed values for the different regions. Dutch and American painters seemed to overestimate the atmospheric clarity, the French and Germans made the air obscure, and the Belgians seemed to get the visibility exactly right.
Our artistic sleuth discovered that if artists are to be believed, the average visibility dropped significantly from 1400 to the end of the 16th century, stayed poor for several hundred years, and then from the middle of the last century seemed ever so slightly to improve. This last was strange, since two developments might lead one to believe that artistic visibility might drop: increasing industrialisation added smoke to the atmosphere, and Impressionism and similar styles lent a certain fuzziness to paintings.