its entire length , now reflected incandescently through the gloom , and using his newfound powers of visualization , he realised that it was not a wall of the tiled variety in-keeping with the rest of the room , but was in actual fact a full-length mirror , and in all probability a reciprocal mirror , giving the clandestine behind the scenes onlooker full and unabridged access to the revulsions of the horror-chamber .