Dietrich, a German philosopher, born at Bremervorde, Hanover, April 3, 1748, died in Marburg, Sept. 24, 1803. He studied at Gottingen, and taught ancient languages at Cassel from 1776 to 1786, when he became professor of philosophy at Marburg. He combined the principles of Locke and Leibnitz. His Untersuchungen uber den Menschen (3 vols., Leipsic, 1777-'98), Theatet (Frankfort, 1704), Idealistische Briefe (Marburg, 1798), and Handbuch der Psychologic (edited by Wachler, Leipsic, 1804), are interesting on account of their investigations in psychology and on the subject of cognition. But his fame rests on his history of philosophy from Thales to Wolf in his Geist der speculativen Philosophic (6 vols., Marburg, 1791-'7).
Friedrich, a German physiologist, son of the preceding, born in Cassel, Aug. 23, 1781, died in Munich, Jan. 22, 1861. He graduated in medicine at Marburg in 1804, and was professor of anatomy and zoology at Landshut from 1806 to 1816, and afterward at Heidelberg till 1849. His numerous works include Zoologie (3 vols., Lands-hut, 1808-'10); Anatomic des Fischherzens (1809); Anatomic und Bildungsgeschichte des Gehirns (Nuremberg, 1816); and Die Physiologic des Menschen (Darmstadt, vols. i. and iii., 1880-'36).