WIA GC/1887/10 | Ruben, Paul to Warburg, Aby 15/10/1887 | mentions Ernst Levy, Wilhelm Kiesselbach, John [Johann Nicolaus] Hertz, Johannes [Hans] Nippen... |
WIA GC/1907/571 | Nippen, Hans to Warburg, Aby 20/12/1907 | cancels appointment; sends wishes to the Christmas meeting of 'Corona' |
WIA GC/1926/708 | Nippen, Hans to Warburg, Aby 24/04/1926 | Warburg told him that Paul [Ruben] was celebrating his 60th birthday; sends birthday greetings... |
WIA GC/1926/709 | Warburg, Aby to Nippen, Hans 26/04/1926 | Paul Ruben's birthday went well; he cannot help him with organising the congress as he will be... |