Otto, Carl
| Wilhelm Speyer an Louis Spohr in Kassel | Frankfurt am Main, Donnerstag 1. August 1833 | 1833080132 |
| Wilhelm Speyer an Louis Spohr in Kassel | Frankfurt am Main, Dienstag 1. Juli 1834 | 1834070132 |
| Louis Spohr an Wilhelm Speyer in Frankfurt am Main | Kassel, Sonntag 6. Juli 1834 | 1834070602 |