Perhaps you should try some spelling variations:
"johann gottfried hagen" » "johann gottfried van", "johann gottfried allen", "johann gottfried anger"
"johann gottfried haber" » "johann gottfried haberler", "johann gottfried grabner", "johann gottfried herder"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("johann gottfried hagen") OR ("johann gottfried haber"))) OR ("johann gottlieb fichte")).
• Removing quotes may allow a broader search: (((( johann gottfried hagen ) or ( johann gottfried haber ))) or ( johann gottlieb fichte )).
• Adding a wildcard symbol may retrieve word variants: (((("johann gottfried hagen") or ("johann gottfried haber"))) or ("johann gottlieb fichte"))*.