WIA GC/1906/96 | Bong, Richard to Warburg, Aby [1906] | encloses a photographic copy of the Rembrandt self portrait in the National Gallery, London... |
WIA GC/1906/97 | Warburg, Aby to Bong, Richard 25/04/1906 | in response to an offer by Bong, Warburg replies as member of the committee of the 'Verein für... |
WIA GC/1908/506 | Valentiner, Wilhelm Rheinhold Otto to Warburg, Aby 13/06/1908 | thanks him for a letter and a copy of Warburg's 'interesting essay' [not clear which]; [Hugo] von... |
WIA GC/1913/164 | Warburg, Aby to Bong, Richard 09/07/1913 | requests information on an illustration published by him |
WIA GC/1913/165 | Bong, Richard to Warburg, Aby 12/07/1913 | replies to Warburg's letter; mentions the library of l'Arsénal in Paris |