Otto Georg Oppenheim, of the banking family, Oppenheim Mendelssohn, married the Mendelssohn heiress, Margerete Mendelssohn, who inherited the Villa Oppenheim in Charlottenburg Park, Berlin, where they housed an important collection of paintings including numerous works by Paul Cézannes, Vincent van Gogh, Édouard Manet, El Greco, Francesco Guardi and Edgar Degas. The present composition is taken from the celebrated pastel by Maurice Quentin de la Tour (1704-1788) which was exhibited in the Paris Salon in 1753 and is now in the Musée du Louvre. A copy in oil, attributed to de la Tour (62 x 47 cm.) was in a sale at Azay-le-Rideau, 13-14 May 1901, lot 85, and then sold, Palma, 22 November 1923, lot 58. A further portrait of d'Alembert, without indication of medium or dimensions, passed through sale, 30 November 1832, lot 19 (see Albert, Besnard, La Tour: La vie at l'oeuvre de l'artiste, Paris, 1928, no. 4, p. 132). Although de la Tour is not known with certainty to have painted in oil, the present portrait would appear to be by a very accomplished contemporary