- Author: Otto E. Ehlers
- Language: German
- Year: 1901
- Author: Otto E. Ehlers
- Language: German
- Year: 1901
- Author: Otto E. Ehlers
- Language: German
- Year: 1895
- Author: Otto E. Ehlers
- Language: German
- Year: 1907
- Author: Otto E. Ehlers
- Language: German
- Year: 1907