Ferdinand von Helmholtz was the son of a gymnasium teacher, his mother, Caroline Penne, being a descendant of William Penn. He was born at Potsdam on August 31, 1821, and died in Berlin on September 8, 1894. After a childhood of ill health, he studied medicine and was for four years a military surgeon; for a year he was teacher in the Berlin Academy of Fine Arts, and afterwards professor of physiology at Königsberg from 1849 to 1855. He was professor at Bonn for three years and was then professor of physiology at Heidelberg from 1858 to 1871, when he was transferred to Berlin as professor of physics. In 1888 he was made president of the Reichsanstalt, organized under his direction. All possible academic and imperial honors were of course conferred on him.
Helmholtz married Olga von Velten in 1849. She died after ten years, and in 1861 he married Anna von Muhl, who died in 1899. One of his sons died in 1889, the other in 1901. His surviving daughter is the wife of Wilhelm von Siemans. Holmholtz traveled more than is the usual habit of the German professor. His visit to America in 1893 will be remembered by many. He seems to have had misgivings in regard to a civilization which has electric lights, while the elements of the art of cookery are 'äusserst Stümperhaft,' and bandits and reporters go at large.
A list of Helmholtz's contributions to science would fill many pages. The essay on the conservation of energy was printed in 1847. Researches of great range and importance, including the invention of the ophthalmoscope, led to his two epoch-making books on physiological psychology—'Tonempfindungen' (1862) and 'Physiologische Optik' (1867). Helmholtz always continued his work in physiological psychology, but his transfer from a chair of physiology to one of physics represented a change in his main interests. His great contributions to mathematical physics, especially electrodynamics, are of almost unparalleled importance.
