The galleries: Sheer poetry in pastoral paradise

Samuel Palmer's romanticism is typified in The Shearers(1833)

William Wordsworth, speaking of spiritual insight, said: "The things which once I have seen I now can see no more." There have been many poets and painters who have had a special visionary quality when young but lost it later.

Conspicuous among them is the 19th-century British painter Samuel Palmer. He grew up in London and was precocious at drawing.

As a young man he left the city to live in the village of Shoreham in Kent, only 30km away but in a rural area.

The great event of his life had been meeting the poet and artist William Blake, who had shown him that all earthly things were but indications of a spiritual life.

In Shoreham, Palmer developed a vision of pastoral life as a special kind of paradise and used this insight to create a set of drawings and paintings of startling originality that vividly expressed the vision.

When he left the village, married, travelled in Italy, started a family and had to please patrons to make a living, he somehow lost his vision. He became a highly accomplished but conventional landscape painter and only late in life managed to achieve something out of the ordinary once again.

All this progress is made clear in a superb exhibition at the British Museum, a show which will transfer to the Metropolitan Museum in New York later in the year.

Palmer's work did not get wide recognition in his lifetime. He was "discovered" in the 20th century and has become one of the most popular and influential of English artists.

Immediately you enter the exhibition you encounter his famous self-portrait done when he was in his early teens. It is a hauntingly Romantic work. His face above a white collar is drawn with great assurance. It is young with a firm mouth and the beginnings of a moustache. But the eyes hold the attention - the gaze is direct but the eyes are deep and dark. It is the face of a spiritual man but one already touched with melancholy.

The rooms where the exhibition is hung are dimly lit because so many of the paintings are watercolours, which fade easily, and the first impression is how tiny they are. Most are no bigger than reproductions of them already seen in books, so there is a sense of familiarity.

The earliest work is done with great skill, although the subjects are conventionally picturesque cottages. Then, suddenly, you are in a room full of works of a quite different order. Conventional skills have been abandoned in favour of a dense stippling manner that makes vegetation into patterns in an almost medieval way.

The light is changed too. Frequently scenes are lit by the moon so there are dark shadows. Or it is twilight or morning, so long shadows are cast.

Under the moon and in the folding of the bosomy hills there are people gathered in groups or solitary men herding sheep or attending to their cattle.

Birds are paired everywhere and in the foreground there may be a rabbit peacefully playing its part in the whole vision. Sometimes these are visions of harvesting, but the standing corn is drawn with full and heavy heads. It is, as the mystic writer Traherne wrote, "Immortal Wheat ... that had stood from Everlasting to Everlasting."

These pastoral works are truly poetic in a tradition that stretches from Virgil to Milton and beyond. Many of these works, and those in the next room, are done in a highly original and inventive technique that combines indian ink with gum arabic and sepia wash.

When Samuel Palmer uses colour the emphasis is on density and glow. The brightest lights are in the clouds or in the rising sun.

In the folds of the hills a church steeple is often seen, emphasising the part that established religion played in this vision of paradise. For Palmer was, in politics, a high Tory and an opponent of change of any sort.

His leaving Shoreham - where he had gathered around himself a group of young artists who called themselves The Ancients because they worshipped the past - may have been partly motivated by outbreaks of the burning of hayricks and barns by farm labourers who did not have the same idealistic view of their work. The rest of the exhibition is devoted to the work Palmer did in Italy after his marriage and on his return to England.

His wife, herself a good artist, was the daughter of John Linnell, a painter who was one of Palmer's teachers and a strong influence on him.

Another pupil of Linnell, Albin Martin, travelled to New Zealand and took up land in South Auckland. He also carried away from his teaching and his travels in Italy a feeling for poetic, pastoral beauty.

The Auckland Art Gallery holds many of his paintings and it is fascinating to see East Tamaki and Otahuhu given the visionary treatment - although never with the same intensity or originality of Samuel Palmer. Yet it does show early Auckland touched with magic.

Towards the end of his long life Palmer took up etching and at least one of his prints - The Lonely Tower, with a solitary bright light at the top of the tower representing poetic inspiration - comes close to the work he did in Shoreham.