It has often seemed the lot of the romantic artist that his work should be fully appreciated only posthumously. Certainly, this was unhappily true of James Arthur O'Connor, who in his last years had to contend with not only failing eyesight but also falling demand for his landscape paintings. When he died in January 1841, his widow was left so impoverished that a financial appeal was organised to support her, with Prince Albert offering 20 guineas to the fund.

Since then, O'Connor's paintings have rarely fallen out of favour and, because he was prolific in his output, they come onto the market with great regularity.

It is indicative of his popularity today that two O'Connor canvases offered by Sotheby's in the auction house's Irish sale last May should have greatly exceeded their estimates. Landscape with Figures beside a River had been expected to make £4,000-£6,000 sterling but eventually fetched £20,700, while The Nut Gatherers (estimate £3,000-£5,000) went for £9,200. The record price paid for an O'Connor landscape was his 1826 painting The Gathering Storm, sold in December 1997 by James Adam/Bonhams for £30,000.

If these figures seem rather low for such an admired artist, it should be remembered that O'Connor's pictures are quite small; The Gathering Storm, for example, measures just over 25 by 40 inches and Landscape with Figures is 15 by 17 and a half inches. Despite their diminutive size, however, they manage to make an impact on the viewer. Strickland correctly remarks, "O'Connor was a painter of deep feeling; his landscapes are solidly and vividly executed and are good in tone and colour".

But when looking at this artist's output, confusion is a possible response, since, as John Hutchinson noted when he wrote the catalogue for a retrospective exhibition in the National Gallery of Ireland in 1985, O'Connor's work may be divided into three distinctive phases - early topographical paintings, mid-period picturesque and late romantic. James Arthur O'Connor was born in Dublin in 1792, the son of an engraver and printseller. He appears to have been largely self-taught but was a lifelong friend of two other contemporaneous Irish landscape artists, George Petrie and Francis Danby, with whom he went to London in 1813. Shortage of money appears to have obliged his early return to Dublin, but soon afterwards he began to find demand for paintings.

His best work from the first period dates from 1818-1819, when he was based in the west of Ireland, producing series of pictures for the Marquesses of Sligo and Clanricarde, as well as a set commissioned by Courtney Kenny and based around his home, Ballinrobe House. This last group are now in the possession of the National Gallery of Ireland and show that O'Connor's primary interest - no doubt reflecting that of his patrons - was in giving as accurate as possible a representation of the scene being shown.

The landscape often tends to lie low on the canvas, with the upper section dominated by wide skies and only occasionally, as in a 1818 view of Lough Derg with Portumna Castle, is there a suggestion of the picturesque sensibility which was to dominate O'Connor's second period.

Beginning around 1820, this middle phase of the artist's career is marked by a move away from specific topographic views towards more imaginary, idealised landscapes. There are two examples of this style in the National Gallery of Ireland, Homeward Bound and Landscape with Figures and Sandbanks. John Hutchinson summarises the style of such pictures as being "delightfully atmospheric" and expressing "a warm, idealised conception of the countryside."

They usually include one or two human figures, which, though small, tend to be placed centrally on the canvas and therefore act as the focal point for the work. Hutchinson suggests that during this middle period, O'Connor was greatly influenced by the paintings of 17th-century Dutch masters such as Hobbema and Ruysdael.

In his late period, by comparison, the principal source of inspiration was the Italian Salvator Rosa. From around 1830 until the end of his career, O'Connor tended to paint landscapes of dramatic intensity in which rock outcrops, darkly brooding skies and windblown trees are the main features. A Thunderstorm: The Frightened Wagoner, dating from 1832 and now in the National Gallery of Ireland, includes all these elements and reflects the romantic movement of the period.

Crookshank and Glin in their The Painters of Ireland describe this work as being "broodingly romantic and very personal". However, they note that even in his most dramatic paintings, helped by the intimate scale on which he worked, there is always a certain quiet quality and "it is this quietness which pervades much of his work early and late and which gives his oeuvre its unity."