John White Alexander, not one of the better-known artists in "Americans  in Paris: 1860-1900" exhibition.

Far from indulging the art set, the current stream of blockbuster exhibitions focuses the art and trains the eye, argues Patrick McCaughey.

THE WORLD IS AWASH with blockbusters.

Melbourne has had its Picasso: Love & War. London has Velazquez at Trafalgar Square, Holbein on the Embankment and Leonardo in Kensington.

Not to be outshone, New York is putting its glamorous foot forward with Cezanne to Picasso: Ambroise Vollard, Patron of the Avant-garde, now joined at the Metropolitan with Americans in Paris 1860-1900. The Frick Collection just down 5th Avenue is transforming itself into the master of the small but dazzling exhibition with Cimabue and Early Italian Devotional Painting.

MoMA is reconstructing Manet''s large, fragmentary work, The Execution of the Emperor Maximilian, normally scattered among Boston, London, Copenhagen and Mannheim. The Whitney Museum has mounted a substantive show of Picasso and American Art. It plays like the Massacre of the Innocents until you get to Jackson Pollock and Willem de Kooning, when the local team begins to take the odd game off the old boy. It''''''''s a relief to find a dud exhibition like the Morgan Library''''''''s effort on Bob Dylan.

If you went further afield, you would find a mighty exhibition of John Constable "six-footers", the big Academy paintings he painted from 1819 onwards, together with their full-size oil sketches at the National Gallery in Washington.

Graham Reynolds, the doyen of Constable studies, now aged 94, thought he would never see the day when these epics of British romantic landscape painting would be brought together. They never have been assembled before and probably never will be again. You can jump on a train from New York and be in Washington in three hours.

If you went north into Connecticut, you would find Canaletto in England at the Yale Centre for British Art and the Hudson River School in all its splendour at the Wadsworth Atheneum in Hartford. If you looked lively, you could just about fit the American exhibitions into an exhausting two weeks.

What does this plethora of major art exhibitions worldwide tell us? Most obviously, the gloomy forecast about the demise of the blockbuster exhibition is as reliable as the White House on the coming of peace and democracy to Iraq. They also dispose of the myth that such exhibitions pander to the art museum audience.

Well, maybe the Met''s Vollard exhibition comes close with its rooms of Cezanne, Van Gogh, Gauguin, Matisse and Picasso. Vollard was the dealer who gave Cezanne his first solo exhibition in 1895 and set him on the path to eternal fame.

Vollard notoriously bought artists'' work cheaply in bulk, hoarded it and then doled it out picture by picture at vast mark-ups to the rising tide of modern collectors.

No artist, save the hapless Rouault, grew rich from Vollard. Far from being the "patron" of the avant-garde, he was its greedy profiteer, its ruthless exploiter. But the 22 Cezannes at the Met make for as great a room of painting as can be seen in New York.

But exhibitions like the National''s Constable or Yale''s perfectly pitched Canaletto show, far from pandering to the audience, are enormously instructive. Instead of wandering glassy-eyed through the medley of vast permanent collections from Italian and Flemish primitives to post-impressionists, blockbuster exhibitions focus the art and train the mind and the eye.

In the Constable exhibition you are continuously asked whether the full-bore Academy version of The Haywain or The Leaping Horse or Hadleigh Castle and so on are better than the equally large and vigorous oil sketches. Sometimes they are, sometimes they''re not. You learn a ton by looking hard.

Canaletto is equally instructive. By leaving Venice for almost 10 years in 1746, Canaletto renewed himself as an artist. London was the Los Angeles of Europe in the mid-18th century, perpetually remaking itself. Canaletto was the perfect recorder of what is past, what is passing and what''s to come.

To keep his hand in, he knocked off some Venetian scenes for his English patrons. The finest of these in the current exhibition is the National Gallery of Victoria''''''''s large and handsome view from the Piazzetta.

It catches a corner of Sansovino''s libreria, then out across the Bacino to the customs house and the mouth of the Grand Canal, ending with Palladio''''''''s great church, the Redentore, on the Giudecca, all caught in the cool grey light of early morning. Marvellous.