Versatile German scientist (1821-1894) known for his discoveries related to visual and aural perception, electrodynamics, and the conservation of energy. Partly-printed DS in German, signed “v. Helmholtz,” one page, 8.25 x 10.25, May 17, 1893. Untranslated prescription issued to Otto Metzing. In very good to fine condition, with scattered light creasing.