WIA GC/1904/340 | Ziehen, Julius to Warburg, Aby 29/11/1904 | congratulations on the birth of the third child, Frede; on the eagle ornamentation; on his illnesses |
WIA GC/1905/653 | Ziehen, Julius to Warburg, Aby 08/01/1905 | thanks for the invitation to lecture in Hamburg; New Year greetings |
WIA GC/1905/654 | Ziehen, Julius to Warburg, Aby26/06/1905 | he cannot leave Berlin for some time; requests information on accommodation in Heligoland |
WIA GC/1905/655 | Ziehen, Julius to Warburg, Aby 02/08/1905 | regrets not having met Warburg in Heligoland; on his stay there |
WIA GC/1910/637 | Warburg, Aby to Ziehen, Julius 25/01/1910 | thanks him for an article; on the need to establish international contacts for scholars... |