EXHIBITIONS / Immaculate conceptions: A new show at the National Gallery paints Claude as a classicist. But the joy of his landscapes lies in atmosphere not allusion

HOW COULD one possibly devise an original Claude exhibition? His paintings are familiar to everyone and resemble each other in a way unparalleled by any other major artist. However many times one returns to his canvases they give the same elegiac messages. Claude is not one of those painters who surprise later generations. He is a poet of memory rather than discovery, and we look to his landscapes for comforting meditation.

At the National, however, we now have a novel interpretation of the master. It is contained more in the commentary than in the choice of pictures, but still the wall captions and catalogue make a point that has seldom, if ever, been heard before. Humphrey Wine, the National's curator of 17th and 18th-century French paintings, believes that Claude's art was steeped in classical and Biblical story and allegory. Think of Landscape with Golden Calf, for instance, or Landscape with David at the Cave of Adallum, or Landscape with the Marriage of Isaac and Rebekah; Mr Wine would have us forget the 'landscape' part of these titles and think more of the legends they portray. Otherwise, he feels, we cannot appreciate Claude as an intelligent artist.

Many people will find it difficult to follow this exercise. Personally, I don't want classical legends in my head when looking at a Claude painting. I find that his virtues are visual more than literary. Furthermore he is visual in a special way. We take his pictures in their entirety. They present themselves to us as a whole, a single harmonious conception. As soon as one starts taking them apart, examining them inch by inch for detail or figure painting, they begin to display faults: flat and unexpressive paint handling, a repetitious and even coarse way of representing water and foliage, unconvincing architectural drawing. Above all, Claude's figures are inept, stuck into the picture like extraneous material. Little wonder that in days gone by it was assumed that they were the later additions of a lesser artist.

These criticisms disappear, however, when we see a Claude painting as a single conception. The National exhibition confirms what we already suspected: that they are best viewed from a little distance. Then their magic appears. We are justified in speaking of 'enchantment'. The exquisitely gradated, unnatural light leads us beyond overt subjects to a mood - one that is undefinable, by reason of Claude's pictorial structures. What is the most important part of his composition? Not the gentle foreground, with its uncertain description of space, nor the sheltering trees at either side of the picture. The significant element is the horizon. That which, in nature, can be least clearly discerned by the eye becomes, in Claude's painting, the influence that renders nearer objects indistinct. You feel that light is created and cast more by the horizon than by the sun or moon. And thus we find an atmosphere more weird than classical.

In this exhibition we sometimes get a deep little shiver from the unusual, especially in the occasional figures that are found in his brown ink and pen drawings. Claude's most affecting painting is Landscape with Psyche outside the Palace of Cupid, painted in 1664. This is the painting from the National Gallery's collection better known as The Enchanted Castle, and said to have influenced that crepuscular poem, Keats's 'Ode to a Nightingale'. Here the dawn or twilight reveals a deep, powerful green (a colour unmatched elsewhere in the exhibition), a choppy and menacing sea, and a castle of intriguing, instead of merely conventional, construction. The picture is more daring for its elongated shape, between the repoussoir at either side of the canvas. And perhaps the painting would have been better still had it not included the figure of Psyche, which is dramatic enough, but for that same reason jarring.

Humphrey Wine, learnedly attending to sources in French and Italian Renaissance translations of Apuleius's The Golden Ass, forms some interesting theories about the iconography of this painting. His speculations are new to me but I found that they affected my reaction to the painting not at all, except only to distract attention from its visual character. I am now the more convinced that Claude is an artist to be appreciated by connoisseurship, and never mind classical knowledge. His landscape was a glorious invention that set the terms of its own appreciation. We do not require words. Nor is it helpful to compare him with Domenichino or Poussin. They were genuinely figure painters in a way that Claude was not. For them, human actions and emotions were vivid and palpable. In Claude the passions of life and literature are only distantly seen.

This is a beautiful exhibition, one which (surprisingly) looks well in the basement galleries of the Sainsbury Wing. The paintings are largely from British collections, augmented by loans from the Continent that give us the second canvas of a pair. Claude was often commissioned to paint complementary pictures but also seems to have liked producing such twins. At the NG there are now four such dual conceptions. It could be that they are linked mainly by subject. Apart from their identical sizes (or unifying coats of yellow varnish) they don't hang together by natural affinity. Again, the wholeness of each of Claude's paintings makes them unsuitable for pairing.

If I owned a castle and collected or inherited Claudes, I wouldn't put more than one of them in a room. Even though Claude gained so much from vagueness, his presence is particularly potent. There is not an enormous number of paintings on display but one does not wish to see more, or not for a day or two. The singular personality of these pictures affected Sir George Beaumont, the romantic connoisseur who owned Landscape: Hagar and the Angel and carried it with him in a special box whenever he went on his travels. Wherever he went the case would be opened and Claude would fill the room. Certainly one would like to own and transport the work of many other artists - but who of them would fill a room so well, as though with the presence of a perfume?

National Gallery, WC2 (071-839 3321), to 10 April.

(Photographs omitted)