of theology. The exterior of the MacNeil house was a family home on 36th and Prospect in Washington, on the former site of E. D. E. N. Southworth's residence. A mansard roof was added to account for the scene in which Chris investigates the scratching noises in the attic. The stairs were padded with half-inch-thick () rubber to film the death of the character Father Damien Karras. Because the house from which he falls was set back slightly from the steps, the crew built an eastward extension with a false front to film the scene. The stuntman tumbled down the stairs twice. Georgetown University students charged people around $5 each to watch the stunt from the rooftops. The interior of Karras' room at Georgetown was a meticulous reconstruction of theology professor Father Thomas M. King's "corridor Jesuit" room in New North Hall. King's room was photographed by production staff after a visit by Blatty, a Georgetown graduate, and Friedkin. Back in New York, every element of King's room, including posters and books, was recreated, including a poster of Pierre Teilhard de Chardin, a theologian on whom Merrin was loosely based. Georgetown was paid a thousand dollars ($ in modern dollars) per day of filming. Locations on campus included both exteriors such as Burstyn's first scene, shot on the steps of the Flemish Romanesque Healy Hall, and interiors such as the defilement of the statue of the Virgin Mary in Dahlgren Chapel, and the Archbishop's office, actually the office of the university's president. One scene was filmed in The Tombs, a student hangout across from the steps. Roizman recalls the scenes in the chapel as the hardest interior to light outside of the house sets. In order to give it the same available-light look as the house interiors for an establishing shot that included the stained glass windows, it was necessary to rig it with 225-amp "Brute" arc lights on parallel mounts. "It was backbreaking work ... but the results were quite pleasing." Exorcism scenes The scenes where Merrin and Karras perform the exorcism were challenging to film. Following the novel, Friedkin wanted the bedroom set to be cold, cold enough to see the actors' breath. A $50,000 ($ in modern dollars) refrigeration system, which Friedkin describes as an air conditioning system powerful enough for a restaurant, was installed that could lower the temperature within to , cold enough that a