The Irish Georgian Society floated a balloon yesterday over the site of the National Gallery's proposed £13 million extension to demonstrate that its 31-metre services tower would be visible over a wide area.
Ms Mary Bryan, the society's conservation officer, said the exercise had confirmed its worst fears that the tower, at just over 102 feet high, would be an "objectionable feature on the city skyline".
The balloon was flown at a measured altitude to mimic the height of the proposed tower, which the British architects, Benson and Forsyth, regard as an essential element of their design, the winning entry in an architectural competition.
But Ms Bryan said it was clear from the balloon experiment that the grounds of Trinity College as well as the "important complex" of Leinster House, the National Library and the National Museum, would be "detrimentally affected".
She said the IGS did not need the National Gallery's permission to fly the balloon because there was public access to the rear of the site from Leinster Lane. It had been attached to a wall some 10 feet from where the tower would be located.
Ms Bryan also pointed out that flying balloons in this way was a "fairly common practice" in Britain in cases where there was a dispute about the visual impact of a new building. However, this is believed to be the first time it has been used here.
Last year the developers of the controversial Hilton Hotel planned for the edge of College Green were required by Dublin Corporation's planners to give an indication of its height. But they used small red pennants rather than balloons.
The Irish Georgian Society, An Taisce and Mr Uinseann MacEoin, the veteran conservationist, have appealed to An Bord Pleanala against Dublin Corporation's decision to grant permission for the National Gallery extension.
They object to several aspects of the scheme, including the demolition of No 5 South Leinster Street, an unlisted mid-18th-century house, as well as an early 19thcentury ballroom to the rear, the only one in Dublin known to have survived.
Regarding the proposed tower, the IGS argues that it would be too high in the "extremely sensitive conservation area" around Merrion Square and that the corporation's planners had not taken sufficient account of its visual impact.
"It is, for instance, both misleading and inadequate to say that the 31-metre high tower would be `glimpsed . . . possibly from College Park'," according to its letter of appeal, which says the planners "wholly disregarded" its effect on Merrion Square.
"Particularly in winter, when the trees are bare, this tower will obtrude on the skyline in views westwards towards Leinster House from most parts of the square. It is incomprehensible that the tower has not been considered in this urbanistic context".
Lancefort Ltd, the company formed by a number of conservationists to fight prominent planning cases, such as the Hilton Hotel and Mr Michael Lowry's house in Co Tipperary, is supporting the appeal, but is not itself among the appellants.
A spokesman for An Bord Pleanala said yesterday a decision on the National Gallery appeal is due to be made by October 4th. It was being conducted by way of written submissions and an oral hearing was unlikely, he added.
