This image shows what appears to be a wall sconce in Katherine Katherine Mackay's (Katherine Alexandra Duer (US1797spouse1) bedroom. The website that posted this image (see below) describes it this way: "A glimpse of the bedroom mantelpiece." This writer does not see a mantelpiece in this image. It looks more like a wall sconce, probably in Keatherine Mackay's bedroom suite.
See Harbor Hill, Clarence Hungerford Mackay's Mansion.