While in the archives of Heidelberg University I was given this photocard, a signed photograph of Hermann Von Helmholtz. What intrigued me was the writing below which says ‘inheritance Ewald.’ Ewald was the assistant of Kühne in the production of many attempts at optograms. Helmholtz was the Professor of Physiology before Kühne. In honour of the reverence felt for Helmholtz it was suggested that an optogram be made featuring an image of Helmholtz.

With thanks to Alexandra Veith for her help in the Ewald mystery.