In the three decades since Death of a Naturalist, I have felt, with the publication of each of his books, that path into new territory opened by his writer's pick (or should it be ploughshare, or spade?) has beckoned me forward, too, in my reciprocal creative role of reader. Although I may not wholly recognise the air and weather of the space the new gathering of poems creates, it gives me a vantage point to look back at the track both poet and reader have travelled.
One of the excitements of the admittedly minority habit of reading contemporary poetry volume by slim volume, as opposed to the Collecteds or Completes of those alive or dead, is this sense of an oeuvre unfolding in real time. A new collection is another instalment, another dispatch from the frontier of that writer's work.
Seamus Heaney's early work, conveniently gathered into the 1980 volume, Selected Poems 1965-1975, with its thick clabber of language and its vivid scenarios from childhood, has become part of the common language of those who read and teach poetry in these islands.
By sharing so generously his glimpses and gazes through "the veil of the usual" and helping us to tune in to "the music of what happens", Seamus Heaney has achieved a unique eminence as poet and man of letters.
These days he is garlanded with honours from the academic world, even the Nobel prize - and yet poems of his can speak to children and adults alike intimately and with grace. As my aunt in Derry said after a gala reading in Derry's Guildhall. "I'm no poetry buff, but I can see this country of ours through the clear windows of his poems, unlike some others I could name. "
The long path, then, that he has been working on with his "squat pen" ever since that first poem of his first book, "Digging" - whither has it brought him and his readers now? Are the new poems ones of direct interest to those of us who teach the reading and the writing of poetry?
Seamus Heaney's work has received remarkably little hostile criticism down the years, although there are many younger writers in Ireland who feel that all the rural stuff is irrelevant to where they are at, that the literary frontline now is the city, and the inner city at that.
Among other readers, within and outside Ireland, there has been an almost opposite concern in recent years: that by gradually, book by book, moving into the abstract and the cerebral, Heaney has been leaving the reality of the rural behind him for the rarefied heights of the academy. Surely the man can't be Professor of Rhetoric at Harvard and Professor of Poetry at Oxford without it doing serious damage to his muse?
Let's go back to the beginning, and trace just one key theme down the years. Seamus Heaney said, many years ago, that writing poems is like making your very own mudpies. In 1978, in a radio talk reprinted in his first book of essays, Preoccupations (1980), he said: To this day, green, wet corners, flooded wastes, soft rushy bottoms, any place with the invitation of watery ground and tundra vegetation, even glimpsed from a car or train, possess an immediate and deeply peaceful attraction.
His first four books - from which the Selected Poems 1965-1975 (1980) are drawn - are rich with wetness from the well of "Personal Helicon" and the delight in "Gifts of Rain" to the ominous "bottomless . . . wet centre" common to the boglands of his childhood's Mossbawn and "the old man-killing parishes" of Denmark's Tollund Fen.
Heaney's writing career has, of course, almost exactly coincided with the visible Troubles.
The ruralness of his childhood territory has also been the setting for appalling incidents of "tribal, intimate revenge". Again from Preoccupations: "I have always listened for poems, they come sometimes like bodies come out of a bog, almost complete, seeming to have been laid down a long time ago. "
The Spirit Level comes out just 30 years after Seamus Heaney's first book,Death of a Naturalist, with its classically wet and dung-spattered title poem, all frogspawn and child's-eye intimations of sex. Down those years, dusts and drought, bloodshed and hunger strike have increasingly threatened to contaminate or even parch the "wet centre" of his poetry.
For all its evocations of lake water and downpours and "that fountain, filling, running,although it is the night", the pivotal book of self-questioning, Station Island (1984), closes with the "I" of "On the Road" meditating a "stone-faced vigil until the long dumbfoundedspiral broke cover to raise a dust in the font of exhaustion."
Increasingly, the poet's first world of malleable, fructifying mud and running water has had to be conjured by an act of will or imagination, as in this tiny epigraph to the book that followed, The Haw Lantern: The riverbed, dried-up, half-full of leaves.
Us, listening to a river in the trees.
More and more, a vision is needed, a trick of the light or sound, an act of faith. By Seeing Things (1991) the poet has learnt at last "to credit marvels". And, in an astonishing poem that is one of Heaney's own favourites in that last collection, he recounts the story of the monks of Clonmacnoise who saw a ship pass overhead while they were in their oratory,and watched a sailor shin down its anchor rope holding his breath, as if their air were water. Two quite contrary perceptions miraculously coexist.
In The Spirit Level the visionary comes full circle back to the messy and the palpable. It is as if, after marvellous travels on which the poetry has often dreamed of home, the poet has come home.
He wades straight in with the very first poem, about a simple musical instrument, "The Rain Stick". Tipping it creates downpour, sluice-rush, spillage and backwash . . .
Who cares if all the music that
is the fall of grit or dried seeds through
You are like a rich man entering heaven
Through the ear of a raindrop. Listen
The book is rich again in the single poems and informal little groups of poems that are what Heaney is best at, celebratory, questioning, compassionate, teasing. And the best of these are back in the first world of dug gravel and wrapped sharping stone, of ploughed field and - yes - the spirit level.
How apt that tool is as the book's title, even to its riddling bubble of absence at the heart of its liquid. There is a sense of fluid balance in these poems' sense of coming home, of returning to the first place, but altered - both resolved and burnished by the being away.
There is no flinching, however, no false burnishing of the material being revisited, or of what has happened and continues to happen while the poet is elsewhere. One of the finest poems is "Keeping Going", dedicated to the brother who has stayed and still farms the land.
Whitewash "lashed on in broad swatches", its smell a "kind of greeny burning" that "brought tears to the eyes", is one of the memory triggers, along with Hugh himself as a boy playing the part of a piper with a "whitewash brush for a sporran" and an upside-down chair for the pipes, his "big cheeks nearly burstingWith laughter".
Against this, in delicate juxtaposition, are other images. The agonisingly slow-motion account of a shooting of a part-time reservist waiting for his lift in the local town: "Grey matter like gruel flecked with blood In spatters on the whitewash." The brother himself, now, "In the milking parlour, holding yourself up Between two cows until your turn goes past, Then coming to in the smell of dung again And wondering, is this all?" It is a commonplace that many writers find their richest seams in childhood memories. Few writers have been able to revisit that seam again and again with such precise attention and such alertness to difference in both seam and self as Seamus Heaney.
Beautiful in or out of the river, The kingdom of gravel was inside you too - Deep down, far back, clear water running over Pebbles of caramel, hailstone, mackerel-blue.
("The Gravel Walks") Looking back now from the vantage point of this new collection of poems, I rejoice that the past 10 years have both deepened and lightened the freight of Seamus Heaney's writing.
In The Spirit Level, as in his Oxford lectures, The Redress of Poetry (1995), his generosity of spirit makes his increasing wisdom of heart, hand and head accessible once more to his old readers, more welcoming to the new.
Catherine Byron's Out of Step: Pursuing Seamus Heaney to Purgatory is published by Loxwood Stoneleigh.
Seamus Heaney will read from The Spirit Level at the Abbey Theatre, Dublin on May 5, the Assembly Rooms, Edinburgh on May 6, Queen Elizabeth Hall, London on May 7 and York University on May 8.
The Spirit Level is published on May 6 by Faber amp; Faber at Pounds 14.99 (paperback Pounds 7.99).
* Inset: beehives from the cover of The Spirit Level.
'On you go now! Run, son, like the devil And tell your mother to try To find me a bubble for the spirit level And a new knot for this tie.' But still he was glad, I know, when I stood my ground, Putting it up to him With a smile that trumped his smile and his fool's errand, Waiting for the next move in the game.
(from The Spirit Level)