Johannes von Kries

Johannes Adolf von Kries (6 October 1853, Roggenhausen – 30 December 1928, Freiburg im Breisgau) was a German physiological psychologist who formulated the modern “duplicity” or “duplexity” theory of vision mediated by rod cells at low light levels and three types of cone cells at higher light levels. He made important contributions in the field of haemodynamics. In addition, von Kries was a significant theorist of the foundations of probability.

When von Kries was at Freiburg (1880–1924), he was called to succeed Professor Emil Du Bois-Reymond as chair of physiology at the University of Berlin, but he declined.

Von Kries has been called Helmholtz's "greatest German disciple".

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