Ireland, and the arts in Ireland, enjoyed something of a golden age during the last quarter of the 18th century, the period to which the beautiful city of Dublin owes so much of its elegance. This period and its prosperity ended with the rebellion of 1798 and the Act of Union that followed in 1801. During much of the following century (until about 1900 when, as George Moore, himself an expatriate Irishman who had "made it" in London, said, "the sceptre of intelligence returned from London to Dublin"), Irish men and women of ambition had to come to England. As George Bernard Shaw, one of the greatest (and most ambitious) of them, declared: "England had conquered Ireland, so there was nothing for it but to come over and conquer England."
The subject of Irish emigration to "the mainland" is almost unmanageably huge - dominated, perhaps, by the story of the "navigators" (navvies) who crossed the Irish Sea, generation after generation, to build England's canals, railroads and motorways. However, R F Foster and Fintan Cullen, the curators of an exhibition at the National Portrait Gallery in London, have bitten off a manageable mouthful of it, devoting their show to Irish involvement in the arts and in politics in Victorian London. If there are no navvies in the story they tell, there is a veritable crowd of playwrights, actors, journalists, poets, politicians, campaigners, models, flower-girls, orange-sellers, painters and draughtsmen, all talking at once. Some of them, the obvious ones - Shaw, Wilde, Parnell, Yeats - are very famous. Most of them are nothing like as famous as they deserve.
The great joy of any visit to the National Portrait Gallery - and part of the raison d'etre of "Conquering England: Ireland in Victorian London" - is, in the good phrase of Cullen, the opportunity it presents to "check the biography against the image". Unfortunately, it is in the nature of the gallery's collection, from which many (though by no means all) of the pictures in the exhibition are drawn, that the subjects of the paintings are often more interesting than the paintings. However, if this is true of some of the pictures in the show, it is certainly not true of the star turn, John Butler Yeats's portrait of his son William. This is an image of "the dandy as Messiah". The poet leans forward, fixing the viewer with his glittering eyes. He is represented in black against deep shadow; his hair is black, his forelock flops over his forehead, and his thin face is caught in a patch of bright light, which glints on the bridge of his spectacles and highlights the edge of his shirt-collar. Somehow the painter has managed to create a visual equivalent of verbal eloquence, and as such it is deservedly one of the emblematic images of the show.
Not all the artists in the exhibition are Irish, though many are. In the words of the ever-quotable Shaw, "every Irishman who felt that his business in life was on the higher planes of the cultural professions" also felt that "his first business was to get out of Ireland". Accordingly, many artists made the crossing and flourished. Sir Martin Archer Shee, the fourth president of the Royal Academy and the first of the Victorian era, was an Irishman but is not included in the exhibition. He was caricatured as "Shee - who must be obeyed" by Harry Furniss, another Irishman, who is. Irish immigrants such as Daniel Maclise, who painted some of the great decorative murals in the new Houses of Parliament, and John Henry Foley, who was responsible for the statue of Prince Albert and the group representing Asia on the Albert Memorial, helped create a visual self-image for imperial Britain.
Maclise also painted Erin, a female personification of Ireland. The model, Caroline Norton, was a granddaughter of the playwright Richard Brinsley Sheridan; the mistress of Lord Melbourne, the prime minister; and an important writer and campaigner in her own right. The images and biographies of several other fascinating women are revived by this exhibition. Anna Jameson, nee Murphy, left Dublin in the 1790s and became an important pioneer art historian. Joanna Hiffernan was Whistler's mistress and model (she's in "Turner, Whistler, Monet" at Tate Britain, too). Courbet painted her as La Belle Irlandaise. Kathleen Newton, another beautiful Irishwoman, was the muse of the London-based French artist James Tissot.
The housemaid Mary Ryan was the subject of many of Julia Margaret Cameron's photographs. Cameron chose her servants for their looks, and Mary's were so spectacular that her photo snared her a husband. She ended life as Lady Cotton, wife of the chief commissioner of Assam. The sitter for the Irishman John Lavery's The Irish Girl got a husband, too. Lavery married her himself - though he later discovered that she was actually Welsh.
"Conquering England: Ireland in Victorian London" is at the National Portrait Gallery, London WC2 (020 7306 0055) until 19 June