BRIEF OHNE UMSCHLAG Focke, Wilhelm Olbers Author: Focke, Wilhelm Olbers Recipient: Haeckel, Ernst Dating: 14.01.1916
BRIEF OHNE UMSCHLAG Focke, Wilhelm Olbers Author: Focke, Wilhelm Olbers Recipient: Haeckel, Ernst Dating: 15.02.1916
BRIEF OHNE UMSCHLAG Focke, Wilhelm Olbers Author: Focke, Wilhelm Olbers Recipient: Haeckel, Ernst Dating: 25.06.1916
POSTKARTE Focke, Wilhelm Olbers Author: Focke, Wilhelm Olbers Recipient: Haeckel, Ernst Dating: 31.10.1916
TELEGRAMM Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Bremen Dating: 18.02.1916