Johann Kühnau, Lieutenant in the Landwehr, fell in the battle of Hagelsberg, bei Lübnitz, on the 27th August 1813, just one of many civilians who joined up to drive the French (and others) from their homeland. According to v. d. Marwitz (Nachlasse, Band. 2 S. 84):

So wie das rechts neben der Batterie vorrückende Bataillon Bornstedt angetreten war, wurde der Lieutenant Kühnau (Doctor der Philosophie und Lehrer am Friedrich-Wilhelms-Gymnasium zu Berlin) durch eine Kanonenkugel getödtet; es fielen auch schon mehrere Landwehrmänner.

I like the little obscure connections. Kühnau was a teacher at the Berlin Friedrich-Wilhelms-Gymnasium, where Otto von Bismarck, whose uncle also took part in the battle at Hagelsberg, was later educated. It was a small world. Perhaps both of them handled the book I now possess.