Van Eyck and Van Dyck
Were not really alike,
Though their names sit quite nicely together;
Dyck liked to paint kings,
And their wives and such things,
While Eyck was a wizard at weather.
Sir Anthony Van Dyck was Flemish, and he flourished in the 1630s. He studied under Rubens, then moved to England and in due course became court painter to James I and, later, Charles. He was one of the most prolific and gifted portrait painters of his day, but he is generally dismissed by connoisseurs as meteorologically irrelevant.
Jan van Eyck, on the other hand, was an expert on the weather. He, too, was Flemish. Born in 1385, he is best known for the altarpiece of The Ado- ration of the Lamb in Ghent cathedral, and for The Arnolfini Marriage, now in the National Gallery in London. But his masterpiece of meteorology is The Crucifixion, which contains an accurate depiction of virtually every common type of cloud.
The scene is the familiar one. It shows a large crowd around the three crosses on Mount Calvary, and the time depicted is the instant when the side of Christ is lanced by the spear of a Roman soldier. The sky, which forms the background, progresses from a deep, deep blue around the zenith to a milky white as the eye approaches the horizon - a precise portrayal of the range of shading clearly visible in the real sky in clear conditions. Also reflecting reality exactly, the vegetation in the foreground is a greeny-brown, while the distant mountains have the characteristic azure hue that results from the scattering of sunlight by the intervening air.
The main cloud type depicted is clearly recognisable as cumulus, showing the characteristic scalloped sides, the rounded tops and - a feature often missed - the flat bases, at more or less uniform height, arranged in line. Elsewhere above the landscape, a long stream of cirrus clouds slopes gently downwards from the centre of the sky.
Although van Eyck would not have been aware that cirrus consists of trails of falling ice crystals, he has captured their appearance to perfection. Above the cirrus is another patch of cloud that resembles cirrocumulus, while near the upper left-hand corner altocumulus lenticularis, or mountain-wave cloud, can be clearly seen. The information given by these clouds, and three windmills, facing the north-west and thereby defining the direction of the wind, allow us to conclude that a cold front had probably crossed an hour or two before, and cleared the sky.