At some time in the early 1800s, a folly was built a few yards behind Newgrange. The folly, with two circular windows, was made of stones taken from Newgrange. In 1882, under the Ancient Monuments Protection Act, Newgrange and the nearby monuments of Knowth and Dowth were taken under the control of the state, and placed under the responsibility of the Board of Public Works. In 1890, under the leadership of Thomas Newenham Deane, the board began a project of conservation of the monument, which had been damaged through general deterioration over the previous three millennia as well as the increasing vandalism caused by visitors, some of whom had inscribed their names on the stones. In subsequent decades, a number of archaeologists performed excavations at the site, discovering more about its function and how it had been built; however, even at the time, it was still mistakenly believed by archaeologists to be built during the Bronze Age rather than during the earlier Neolithic period. In the 1950s, electric lighting was installed in the passageway to allow visitors to see more clearly, whilst an exhaustive archaeological excavation was undertaken from 1962 through to 1975, the excavation report of which was written by Michael J. O'Kelly and published in 1982 by Thames and Hudson as "Newgrange: Archaeology, Art and Legend".