Each day stressed pedestrians - workers, students and shoppers - as well as more leisurely tourists, pass the elegant door of 19 Dawson Street, Dublin, at varying speeds and levels of preoccupation.

Countless numbers have never cast a glance at the understated but gracious Georgian double-fronted building, which is flanked on one side by the Mansion House, built in 1715, and on the other by St Ann's church, dating from 1720. Those who have noticed it may have remarked upon the presence of what appears to be a private period mansion on a modern city street of shops and offices. They would be right.

More than 200 years ago it was a private home. The exact date of its construction is uncertain, but the plan and style of the building suggest it was completed in the early 1750s. For the past 150 years it has been the second and most permanent home of the Royal Irish Academy. When it took up residence in Dawson Street, having moved from Navigation House on Grafton Street, the academy was 66 years old.

It was a survivor of the Act of Union, with its loss of an independent parliament; a witness to the French Revolution, the United Irishmen in 1798, and the Famine; and the possessor of a remarkable legacy that had been shaped by daring minds.

Founded in 1785 by James Caulfeild (1728-99), fourth viscount and first earl of Charlemont, creator of Dublin's magical Casino, the academy has always been a working institution. Charlemont's house at Rutland - later Parnell - Square was briefly used as a meeting place for its first members, such as General Charles Vallancey, William Burton Conyngham, James Kearney, Henry Ussher, Thomas Bernard, Richard Kirwin and Richard Lovell Edgeworth.

The story of the Royal Irish Academy, with its aim of "promoting the study of science, polite literature and antiquities", offers a vivid chronicle of Ireland's intellectual and cultural life since the late 18th century.

Its list of members and former presidents reads as a colourful roll-call of Irish visionaries. Its collection of antiquities, catalogued by William Wilde, provided a rich base for the National Museum of Ireland, which opened in 1890.

Genius, scholarship, energy, dedication and, above all, a relentless curiosity dominate its history and characterise its personalities. There is also the range of subjects represented: geology, botany, biology, archaeology, astronomy, social and political history, language and geography.

From the evolution of the landscape to the mapping of towns, the setting up of a network of meteorological observatories and the tracing of human genes, the academy has provided inspiration and encouraged pursuits as unique and as vital as the protection of our heritage, the rediscovery of place names and the exploration of the natural world.

It is the story of gentleman antiquarians and of determined scientists, of classicists and pioneering mathematicians. Yet for all its achievements, such as the Clare Island Survey of 1909-11 - the most ambitious natural history project undertaken in Ireland, as well as the world's first significant biological survey of a specific area, published on April 15th, 1915 - this singular, multidisciplinary all-Ireland body defies our age of hype. Ireland's largest academic publisher remains discreet to the point of anonymity.

Respected internationally as a scholarly institution, the academy owns one of Ireland's great libraries, with some 80,000 volumes and the world's finest collection of Irish manuscripts, including the sixth century Cathach (Battler), a copy of the Psalms of David controversially copied in Latin by St Colmcille, and Lebor Na hUidhre (The Book of The Dun Cow), the oldest surviving manuscript written entirely in Irish. It also contains the Haliday collection of some 30,000 pamphlets, which date from the 17th to the 19th centuries and reflect all aspects of Irish life.

IT IS true that the academy suffers from charges of elitism. Academic excellence is the only criterion for admission. Yet its scholarship has always been of a practical as well as an intellectual nature. The Royal Irish Academy has contributed hugely to the publication of the findings of archaeological excavations. Any interested reader may use the library by agreeing to comply with standard library regulations.

"The library actively supports an open-door policy" says Siobhan O'Rafferty, its librarian.

Among the books are complete sets of journals, Irish antiquarian books, maps, the Ordnance Survey letters, articles and an extensive classical section. The library has benefited from bequests such as Thomas Moore's personal collection, which reflected the tastes of an Enlightenment gentleman.

Although never a member, the self-taught naturalist Cynthia Longfield donated her science library to the academy in 1979. Among the books she gave it were the 10 volumes of Jean-Henri Fabre's Souvenirs Entomologiques, still housed in her glass-fronted display cabinet.

Among the academy's ongoing research projects are Focloir Stairiuil Na Nua- Ghaeilge; the 10-volume A New History Of Ireland (the final two volumes of which are approaching publication); the Dictionary Of Irish Biography; the New Survey of Clare Island; Irish Origins: the Genetic History and Geography of Ireland; the Irish Historic Towns Atlas series, edited by Anngret Simms, Howard Clarke, Raymond Gillespie and John Andrews, which has already to date mapped the genesis of 10 Irish towns, with Dublin and Belfast nearing completion, is part of a wider European project; and the magnificent Atlas of Ireland (1979), chaired by Joe Haughton remains a magnificent achievement.

Membership has always been balanced between the sciences and the humanities. The members are nominated, elected from within the academy for life.

Former presidents include William Rowan Hamilton, Humphrey Lloyd, Samuel Ferguson, William Parsons, the third earl of Rosse, John Kells Ingram, R.A.S. Macalister, Robert Lloyd Praeger, John Lighton Synge, Frank Mitchell, Bill Watts, Ken Whitaker and James Dooge. Among the 275 current members are the archaeologists George Eogan, Peter Harbison and Michael Ryan, the historian Joseph Lee, the geographer John Andrews, Patrick Lynch, Edna Longley, Seamus Heaney and Conor Cruise O'Brien.

Many of the most remarkable people active in Irish life during the past 200 years have been associated with the academy. To read its history is enriching but humbling.

David Spearman, a mathematician and former vice provost of TCD, was elected president in 1999 and is naturally proud of the institution he heads.

"Like many of the other European academies, it was founded in the 18th century. The academy strongly reflects the spirit of the Enlightenment: a belief in the importance of reason, of free and open discussion and of rational analysis," he explains.

"The significance of the contribution that the academy can make has perhaps not been fully recognised in the recent past. But there are already clear signs of a growing awareness of the importance of what we are doing, and that we will increasingly be looked to for objective opinion and expert advice."

The academy's reading room is always busy with the loud industrious silence common to libraries. The clock ticks, readers tiptoe, stomachs growl. But it is a relaxing place.

It was in the meeting room that Praeger read the "general introduction and narrative" of the Clare Island Survey on June 22nd, 1914, and some six months later its general summary. Outside on the main staircase, under a ceiling of fine plaster work, a bust of Praeger, the 26th president, is displayed beneath a portrait of Charlemont, the first. Separated only by time, they shared a vision that remains alive in the institution they loved.