On the Zuiderzee by Valkeveen. From left to right: Alphons Diepenbrock, Gustav Mahler, Willem Mengelberg. Sitting: M. Mengelberg-Wubbe, Hilda G. de Booy-Boissevain, P.J. Boissevain and Maria B. Boissevain-Pijnappel. Behind the camera: Han de Booy, husband of Hilda de Booy-Boissevain.