Brühl built (probably in 1787) a small observatory at his villa at Harefield, and set up there, about 1794, a two-foot astronomical circle by Jesse Ramsden, one of the first instruments of the kind made in England.
Lady Alice, Dowager Countess of Derby was already living at Harefield Place, although she became concerned that Lord Castlehaven, the second husband of her eldest daughter, Lady Anne Stanley, would attempt to claim her estate in the event of her death.
The Royal Brompton and Harefield NHS Foundation Trust runs the Royal Brompton Hospital in Kensington and Harefield Hospital in Hillingdon, London, England.