ART / The eyes have it in Paris: He was huge in New York - in Paris he is slimmer and more striking. James Hall on Matisse and Walter Elkan on his great Russian patrons

No statement has done so much damage to an artist's reputation as the one made by Matisse in Notes of a Painter (1908): 'What I dream of is an art of balance, of purity and serenity, devoid of troubling or depressing subject matter, an art that could be for every mental worker, for the businessman as well as the man of letters; for example, a soothing, calming influence on the mind, something like a good armchair which provides relaxation from physical fatigue.'

At time of writing, Matisse was known as le prince des fauves ('the prince of the wild beasts'), but he was already changing his spots. His agitated Fauve style, with its discrete blobs and slithers of paint, was being replaced by simplified forms, bold arabesques and broad fields of bright colour. This new style, and Notes of a Painter, were a double defence against the charges of incoherence. Ever since, however, Matisse's detractors, and rivals such as the Cubists, have used his serene dream to prove that he was little more than a haute couturier. Picasso is said to have said: 'Matisse is a cravate - a coloured necktie.'

The marvellous exhibition at the Pompidou Centre, which covers the key years from 1904-17, should dispel this self-inflicted myth once and for all. It is a truncated version of the Museum of Modern Art retrospective, but what it loses in comprehensiveness it gains in quality. To experience Matisse neat is awe-inspiring and emotionally draining. You feel you are in the presence of an artist who has grasped the central paradox of sublime art - that sensory saturation is the mother of sensory deprivation.

Since Matisse had chairs on the brain around 1908, we would do well to study the seating arrangements here. The celebrated pair of pictures of The Young Sailor, from 1906-7, demonstrate that sitting had become an increasingly complex business. The first version, in which the paint seems to have been scrubbed on, is still relatively credible as a three-dimensional image of a strapping lad lounging on a wooden chair. His left arm rests on the back of the chair so that his hand can prop up his head, while his right hand clamps chair seat and thigh together. The front-on orientation of his body serves to flatten it, but depth (which is crucial to the idea of chair-ness) has not been sacrificed entirely. The hawk-like concentration of his eyes on an area to our left suggests that objects still have a plottable position in space and time. Objects still, as it were, 'sit'.

The second version is constructed from heraldic slabs of strong colour. It has a saucy pink background. The sailor floats free of the chair, his body tumescing pneumatically. He has become a bulging sail, and the strutted chair a hard-pressed mast. The picture pushes forward drunkenly. The boy's eyes are wide open, the eyeballs out of sync. They tell us one thing: deep seeing is no longer possible. There is nowhere for eyes to rest or sit. We must let our own eyes rock and roll across the picture surface.

This disconcerting image says more about rootlessness than it does about homeliness. The figure gains plenitude and fulfilment at the price of unseating itself, of lifting off. But maybe it's time to switch metaphors. Instead of a sail straining at a mast, how about a swollen mussel emerging from a narrow shell? This reading makes more sense once we consider the broodily luminous Bathers with a Turtle (1908). Here three naked female figures cluster round a turtle on an empty beach. Their bodies adhere to a background daubed with horizontal bands of turquoise and blue. The central figure stands grief-stricken with her hands in her mouth; the one on the left squats down and feeds something to the turtle; and the one on the right sits - it would seem - suspended in mid-air. As so often, Matisse's handling can be quite gauche and acerbic. The surface tingles and is brittle with revisions.

The exhibition organiser John Elderfield, in an otherwise searching catalogue essay (the best I have ever read on Matisse), calls it an 'absurdity worthy of Samuel Beckett', and says that this 'pessimistic' picture rejects 'correct interpretation'. Yet its meaning is surely quite straightforward. Folklore has it that snails, in contrast to man, are at home everywhere because they carry their house on their back. So too with the turtle. It is an amphibian with a personalised protective carapace, whereas the three women are 'unaccommodated'. That is why they look down at it longingly and mournfully.

Matisse's art involves the most intense kinds of exposure. His subjects have shed their shells, and they have shed shade. Even in his interiors, the darkness is always visible, saturated with luminosity. According to Elderfield, 'we feel blinded by their beauty'. Matisse's last great paper cut-out, The Snail, in the Tate Gallery, is a case in point. It is not dark and earthy, but a crazy paving of brilliant colour. At the time, Matisse explained that he had found an image in his mind 'purified of the shell'.

Was Matisse thinking of Venetian painting when he made his 'good armchair' gaffe? He may well have been, because in 1907 he toured Italy, Venice included. Yet characteristically, the artists he said he admired were hard-edged primitives like Giotto and Uccello rather than the soft-focus fops of La Serenissima. Still, as we can amply see in 'The Century of Titian', at the Grand Palais, Venetian painting is far more than armchair art.

Venetians were the ultimate amphibians, commanding land and sea, and their art is a miraculous synthesis of the four elements - earth, water, air and fire. Yet the defining mood of their art is mournful reverie, and its defining moment is early evening. Such things speak of absence and of loss, of not being in quite the right place at quite the right time.

The exhibition has 291 paintings, drawings and prints, and though most of these have been drawn from French collections, many major foreign loans have also been secured. At its heart are eight of the Louvre's newly restored Titians. Unlike the Royal Academy's 'Genius of Venice', a full history of Venetian art in the 16th century has not been attempted. Instead, Michel Laclotte has chosen to trace the overwhelming impact that Giorgione and his pupil Titian had on Venetian painting. It is a thoroughly unoriginal thesis, but if it ain't broke, why fix it?

Giorgione died in his early thirties in 1510, and less than 10 works are now firmly attributed to him. A much longer list of Giorgionesque works has been credited to the young Titian or to others in Giorgione's circle. But whereas the four 'Giorgiones' in the 'Genius of Venice' were all attributed to Titian and lesser-known acolytes, Leclotte has thrown caution to the wind. Here we have 18 works claimed to be by the great ghost in the Venetian machine.

There is an unprecedented array of 15 half-length portraits. Some, such as the singer and flautist from the Villa Borghese in Rome, lack conviction, but the Portrait of a Young Man from Budapest feels a good bet. Elegantly androgenous, the dapper lad rests his right elbow on an imprisoning parapet, and gazes wistfully away to the left. He hovers the exquisite fingers of his right hand over the slit in his blouse which travels half way down his chest. As so often in Venetian art, the most satisfactory cure for loneliness is narcissism.

It is eye- and mind-boggling to think that in Paris there is all this - and more. A huge Egyptian exhibition is also at the Grand Palais and at the Musee d'Orsay there is an intriguing pot-pourri of artworks that were all produced in 1893: Symbolists like Gauguin and Burne-Jones rub shoulders with Neo-Impressionists and Realists. Back in London, we dream on . . .

Matisse continues until 21 June at the Pompidou Centre; Century of Titian continues at Le Grand Palais until 14 June.

(Photograph omitted)